Semantic module 2. Method of inspection of patient with tuberculosis
General approaches to diagnostics of tuberculosis.
Special methods of exposure and diagnostics of tuberculosis (microbiological diagnostics,X-Ray diagnostics, tuberculinodiagnostics). Curation of patients.
General approaches to diagnostics of tuberculosis.
Clinical examination of tuberculosis patients
The methods of investigation of respiratory (tuberculosis) patients are conveniently divided into three groups.
The First group – compulsory (obligatory) methods, which embrace clinical examination of a patient (complaints, anamnesis, examination, palpation, percussion, auscultation), thermometry, X-ray investigation (fluorography, X-raygraphy, X-rayscopy), sputum analysis for MBT, Mantoux tuberculin test (with 2 TU), general blood and urine test.
The Second group – additional (supplementary) methods, which include repeated sputum analysis (bronchial lavage water) for MBT, tomography of the lungs and mediastinum, protein-tuberculin tests, immunologic tests, instrumental examinations (bronchoscopy, biopsy, bronchography, pleuroscopy).
The Third group – facultative (optional) methods: investigation of the outer breathing function, blood circulation, liver and other organs and systems.
Tuberculosis is an infectious disease, caused by MBT, and is characterized by the development of specific inflammation in injured organs and polymorphism of clinical symptoms – intoxication and local syndromes.
Within the range of the likely evidences of the general TB intoxication, the most frequent are general weakness, indisposition, drop of the ability to work, sweating, appetite drop, weight loss, sleep disturbance, body temperature rise. Body temperature in TB patients can vary – it can be normal, subfebrile, febrile and even hectic. However, the most often it is subfebrile, which is characterized with pronounced lability and the absence of monotony. Patients often endure the high temperature easily.
At the beginning of the illness the sweating is low. Profuse sweat, mainly at night, are characteristic of pronounced exudative, caseous specific processes.
The local manifestations of lung tuberculosis are: prolonged cough, sputum secretion, haemophthisis, chest pain, shortness of breath.
Cough is the most frequent symptom in patients with lung TB. At the initial stages of the process the cough is quiet, not frequent, in the form of light constant hacking cough. Persistent convulsive loud cough is characteristic for patients with tuberculous bronchoadenitis and tuberculous endobronchitis.
At the beginning of the illness, the sputum caot be secreted or can be secreted only a bit. With the progress of the tuberculous, in particular the distructive, process, the patient may secret up to 200 ml of the sputum, which can be mucous or mucous-purulent and can be without any unpleasant smell.
Chest pain is often present already at the beginning of the illness , which is caused by the extensive process in the lungs. Acute sudden pain appears at spontaneous pneumothorax.
Dyspnea is not characteristic for the initial forms of TB, except for the miliary TB and the exudative pleurisy. At the chronic extensive process, complicated with breathing or pneumo-cardial insufficiency, dyspnea can be brightly expressive.
Hemoptysis and bleeding may be present at any form and phase of the process, but more often – at destructive forms of TB, and more rarely – at posttuberculous pneumosclerosis with bronchoectasia. Hemoptysis is characterized by the presence of veins, blood admixtures in the sputum and of separate blood spits. At pulmonary bleeding, much more of pure blood is coughed up in one time (over 10 ml), continuously or with breaks. Blood is usually bright-red, foamy, with tiny air bubbles; it doesn’t have tendency to coagulation. After the bleeding or hemoptysis stops, blood clots are coughed up for several days more; and due to the blood aspiration, the boby temperature rises.
The beginning of tuberculosis illness may be without any symptoms, subacute and rarely – acute. While interviewing a patient it is very important to find out a fact about his contacts with tuberculosis patients. To the point, persons, living amidst nidi of tuberculosis infection (the patient, suffering from the tuberculosis, who excretes the mycobacteria, the place where he lives and people, who live with him), 5-10 times more often contacting tuberculosis. Of great importance is the information about endured in the past “flu”, pneumonia, exudative pleurisy, under which mass tuberculosis can run; accompanying illnesses, working conditions, harmful habits etc.
The formal examination at initial forms of tuberculosis reveals no patient’s visible abnormalities. However, in most patients, at the more advanced stages of the disease one can find manifestations of tuberculosis intoxication: eyes lustre, hectic blush on the background of a face pale skin; paraspecific tuberculosis manifestations (knotty erythema, keratoconjunctivitis, phlyctenae) enlarged peripheral lymphatic nodes, fistulas or scars after them, chest deformation. Palpably: often lowered skin turgor, muscles tone, micropolyadenite, positive “fork-shaped” symptom (putting 2 fingers above the sternum from the both sides of trahea, it is possible to feel its dislocation to the side of injury), which is observed at unilateral lung cirrhosis, atelectasis. Increased voice tremor above infiltration or cirrhosis zones, weakened – at exudative pleurisy, pneumothorax.
Percussively: shortened and dull percussioote is defined above the airless lung tissue or in the spheres of its lowered (weakened) pneumatization at infiltrates, nidus–fibrous transmutations (changes) and exudative pleurisy. Tympanic note occurs above the strenuous spontaneous pneumothorax, a gigantic cavity. However, more often shortening of percussioote is observed above the cavern.
The standing hight of the lungs apex and the width of Crening’s spheres (fields) decreases as a result of nidus, infiltrating or fibrous changes in the upper sections of the lungs.
Auscultation should be performed consistently above the symmetrical sections of the lungs at quiet deep breathing with the patient’s half-opened mouth. With a view to provoke crepitation, the patient should be asked to cough slightly at the end of the expiration. Herewith the doctor should stay at the patient’s side to avoid infestation.
It is necessary to find out the type of breathing (vesicular, bronchial, mixed) and additional murmurs (moist, dry rales, crepitation, pleura friction murmur). Weakened vesicular breathing is defined at lung emphysema, exudative pleurisy, pneumothorax and high caloric diet; strengthened – at emaciation, cirrhosis and lung infiltration process. Rough or bronchial breathing may be heard above a thickened lung tissue (infiltrate, cirrhosis, fibrosis), amphoric respiration – above a large cavern with fibrous walls and a wide draining bronchus. Important from the diagnostic point of view are local moist rales, which are auscultated after the hacking in the “alarm zones”: frontally, above and beneath the clavicle, from the behind above the lungs, near a scapula spine and between scapulae. Local small-bladdered moisty rales are the indication of the beginning of lung tissue destruction, while those of medium-and-great-bladdered – the indication of a cavern. In addition to this, medium-or-great-bladdered rales above the upper sections of the lungs is an essential indication of the decay cavity. Dry rales occur at bronchitis, whistling ones – at bronchitis with a bronchospasm. At dry (fibrinous) pleurisy the murmur of pleural rub is heard.
Is directed for prevention infection of healthy people from ill on tuberculosis people and animals. Infections agent of tuberculosis importance of infection, its resourse and ways of transmission – there are the base of study.
Sanitary prophylaxis includes sanitary locus of tuberculosis infection, sanitary and vet care, and early revealing, isolation and treatment of ill on tuberculosis.
Epidemioligical locus includes ill persons, who discharge micobacteria, house, where ill person lives and people with whom he lives. Bacteriodischarger is a person, who discharge MBT with a help of any methods of trials and clinico-radiological features of active tuberculosis process.
Disinfection , test of persons, who were in contact with ill, chemoprophylaxis, isolation of children from bacteriodischarger, sanitation up bringing of ill, improvement conditions of living standarts and also treatment of desease are the most epidemiological factors of tuberculosis infection.
Prophylaxis is performed because epidemic danger, including such factors :
1) spreading of bacteriodischarge
2) when there are children and tecnagers in the family
3) sanitary conditions in which ill-person is living.
The most important factor is spreading of bacteriodischarge, which is devided into:
1) greate, when micobacteria in spit is present in simple bacteria scopy
2) small, which includes methods sowing
3) formal, when bacteriodischarge stops.
Focus of tuberculosis infection is devided into 3 groups.
1-group: focus, where ill person with big or small bacteriodischarge live, but there are children and tecnagers in the family, which live poorly.
2-group:ill person with small bacteriodischarge and all members of the family are adults (without children) or illwwith formal bacteriodischarge and children are in the family.
3-group:ill person with formal discharge and in the family live only adults.
Early detected of tuberculosis
The sick men on tuberculosis may be detected:
– timely
– intimely
– lately.
The methods of detected the tuberculosis in time are the following ones:
1) prophylactic inspection:
– children – tuberculine diagnostic
– teenagers – tuberculine diagnostic, in 15 years old in addition fluorography
– adults – fluorography
2) detected in case of appealing for medical help
3) watching for the persons with high risk to become ill in tuberculosis.
The causes of tuberculosis intimely detected are the following ones:
– non-attentive attitude patient to his health
– peculiarities of tuberculosis course
– mistakes of doctors.
Special methods of exposure and diagnostics of tuberculosis (microbiological diagnostics,X-Ray diagnostics tuberculinodiagnostics).
The laboratory diagnostics of tuberculosis. Methods of revealing mycobacterium of tuberculosis. Atipical MBT. Sensitivity of MBT
The source of infestation of human beings are tuberculosis human patients and animals secreting tuberculosis mycobacteria. The material for revealing MBT are sputum, bronchial lavage waters, faeces, urine, fistula pus (matter), pleural cavity exudate, spinal fluid, punctates and bioptates of various organs and tissues.
Sputum examination for MBT is of great epidemiological and clinical importance. When there is no sputum or it is scarce, expectorants, irritant aerosol inhalations, bronchi lavage are administered (fig.1).
Methods of Revealing Mycobacteria:
1. Bacterioscopy is one of the main methods of revealing MBT; it includes ordinary bacterioscopy, flotation and luminescent microscopy. An ordinary bacterioscopy is accessible to all, simple and quick to do. In smears, coloured according to Tsil-Nilsen, MBT are revealed wheot less than 50000 microbic bodies are present in 1 ml of pathologic material. According to the “instructions for bacteriologic diagnosis of the tuberculous infection” of the Ministry of Health Protection of Ukraine, order № 45 dtd. 06.02.2002, MBT can be revealed if their quantity is 5000 – 10000 bacterial cells in 1ml of the pathologic material. Under the microscope MBT look like bacilli of the red colour on the blue background.
Flotation method (enrichment or concentration of MBT in a small volume, caused by droplets of benzine, benzole, xylol or toluene on the surface of a retort ring) is applied in cases when there is a small number of MBT in the pathologic material and at negative results of ordinary bacterioscopy. Flotation method provides for 10-15 % more often revealing MBT in comparison to direct bacterioscopy.
Luminescent microscopy is based on the ability of MBT, coloured with fluorochroms, to illuminate under the influence of ultraviolet rays and performing microscopy at small magnification, increasing by 15-30 % the sensitivity of the method in comparison to direct bacterioscopy and by 10 % in comparison to the flotation method (fig.2).
2. Bacteriological method consists in the following: sputum or another material, after preliminary special treatment, is sown outritive media (hard, blood, semisynthetic) (fig. 3). More often hard egg Lewenstein-Yensen medium is used. 20-100 microbial bodies in 1 ml of sputum is enough for revealing MBT culture. The first colonies appear on the 14-30-th day of cultivation. The negative result is given only in 2,5-3 months from sowing. This method of revealing MBT allows to define their vitality, virulence, group (differentiate from acid resistant saprophytes and atypical MBT) and species origin, as well as their resistance to antimycobacterial preparations. In addition to this, according to the data of bacteriological examination quantitative essessment of bacterial secretion is made: miserly-up to 20 colonies on a nutrient medium, moderate – from 20 to 100 and massive – more than 100 colonies.
Fig. 3. Culture of mycobacteria tuberculosis at hard egg medium
Therefore, the culture result must depict not only the qualitative characteristics (positive or negative), but also a quantative evaluation (colonies №). For that it is recommended to use Table 1 (National Antituberculous Programme, 2000).
Table 1
WHO scheme of the evaluation of the results of cultural examination for
M.tuberculosis
|
Colonies quantity |
Result evaluation |
Characteristics |
|
1-19 colonies |
Positive |
Individual colonies (miser bacterial emision); bacterioscopy of the pathologic material scarcely reveal individual mycobacteria |
|
20-100 colonies |
1+ |
Moderate bacterial emission; bacterioscopy of the pathologic material reveal individual mycobacteria in each field of vision or only single ones – in the preparation, but not less than five |
|
100-200 colonies 200-500 colonies (almost universal growth) Over 500 colonies (universal growth) |
2+ 3+
4+ |
Massive bacterial emission; bacterioscopically – 10 and more mycobacteria in each field of vision
|
|
Germination of common microflora |
Germination – repeat inoculation |
|
3. Biological method. It is infection with sputum or another pathologic material of guinea-pigs, which are highly sensitive to MBT. A biological testing is the most sensitive method of revealing MBT, so far as in laboratory animals tuberculosis develops after the introduction of the material in which there may be less than 5 microbial bodies in 1 ml. However, it should be noted that MBT are stable to chemical preparations, particularly to isoniazidum, avirulent for guineapigs. That is why various methods of microbiological examination should be used for revealing MBT in pathological material. Generally, before starting to treat a patient, he should undergo complex bacteriological examination: three times direct bacterioscopy of sputum or, when it is absent, three times examination of the material after provoking inhalations or bronchial rinsing waters; with negative results – three times examination by flotation method; three times sputum sowing on a nutritive medium, irrespective of the results of the previous examinations, with a view to define MBT sensitivity to antimycobacterial preparations the examinations are made in accordance with the recommendations of the World Health Organization.
The repeatedness of the patient examination for TB revealed for the first time in the dynamics of chemotherapy (acc. To WHO recommendations) is given in Table 2.
Table 2
The repeatedness of the patient examination for TB revealed for the first time in the dynamics of chemotherapy
Period from the firstof therapy (month)
|
Obligatory minimum |
||
Bacterioscopy |
Inoculation |
Determination of drug resistance |
|
|
0 |
х 3 |
х 3 |
х 3 |
|
At the end 2 (3) |
х 2 |
х 1 |
х 1 |
From the first 5 |
х 2 |
х 1 |
х 1 |
|
At the end 6 (8) |
х 2 |
х 1 |
х 1 |
Notes:
x if at the end of the second month of the treatment the results of bacterioscopy of MBT smear is (+), it’s necessary to make bacterioscopy at the end of the third month;
xx if at the end of the sixth month of the treatment the results of bacterioscopy of MBT smear is (+), it’s necessary to make bacterioscopy at the end of the eighth month.
The usage of antimycobacterial preparations provokes the development of drug resistance to MBT. There are primary and secondary drug resistance.
The primary drug resistance – is MBT stability, in the patients who were TB revealed for the first time; this stability is the result of the infection with stable MBT strains.
The secondary drug resistance appears in the process of continuous irrational antimycobacterial therapy.
According to WHO data, the frequency of the primary drug resistance to any preparation is 10.4% average, and the secondary – 36 %. In
Nowadays immunologic and molecular-genetic methods are applied for etiological identification of tuberculosis. The most promising of them are immunoenzymic and radioimmune methods of defining mycobacterial antigens which are based on the application of monoclonal antibodies. Molecular-genetic method of polymeraze chain reaction consists in revealing in biological material (sputum, tissues; lavage, pleural, spinal fluid etc.) of mycobacterial DNA. The examination results may be obtained in 3-4 hours.
The determination of MBT sensitivity to antimycobacterial preparations is of paramount importance for the treatment tactics, correction of antimycobacterial therapy and the illness prognosis. MBT sensitivity to antituberculous preparations is defined by the preparation minimum concentration, which inhibits MBT growth on the nutritive medium. MBT are considered to be sensitive to either preparation if less than 20 colonies have grown in a test-tube, with abundant growth in the control. The culture is supposed to be stable if more than 20 colonies have grown. MBT are considered to be stable if they grow at the concentrations of the preparation in 1 ml of the nutrient medium: for isoniazidum – 1mkg, rifampicinum – 20 mkg, streptomycini – 5 mkg, ethambutolum – 2 mkg, all other preparations – 30 mkg.
Blood examination. The main reasons of changes in peripheral blood of tuberculosis patients are intoxication and hypoxia. At initial forms of tuberculosis a hemogram is normal or with inconsiderable deviations. In recent years hypochromic anemia is more and more often observed, however at chronic lingering course of the spread specific process, with the intensification of the phenomena of lung insufficiency and hypoxia, compensatory increase of erythrocytes number and hemoglobin is possible. In general, for more serious clinical forms of tuberculosis slight leucocitosis (9,0-15,0 х 109/l) is characteristic, percentage of bacillarnuclear neutrophiles, lymphopenia, monocytosis, eosinopenia increase, ESR is speeded up, as well as the decrease of albumin-globulin coefficient sets in with the relative increase of alpha-2 and gammaglobulins.
Urine examination. In patients with expressed tuberculosis intoxication, proteinuria, erytrocytes and leucocytes in urine may be observed. With intoxication decrease the pathological changes in urine disappear. However, if there is amiloidosis of internal organs, in particular kidneys, hypoisosthenuria is typical, stable proteinuria, increased number of erythrocytes, leucocytes in urine, as well as emergence of cylinders.
DIAGNOSTIC LABORATORY METHODS FOR TUBERCULOSIS
Introduction
In mycobacteriology labs, we continue to use mainly the old, proven methods. This is so even in rich countries, where it would be less of a problem to use the newer and more expensive or technically demanding techniques. Smear microscopy, for instance, a technique which is over 100 years old, continues to be included in every investigation for TB, simply because it is all over the world a valuable technique which is helpful in many cases. Because of the higher proportion of smear-positive cases and the rarity of other mycobacterial pathogens, this is even more true in TB high-prevalence countries. The reliance on microscopy for TB in these countries is not in the first place because of lack of money for something better. Newer techniques exist, but some of them have serious shortcomings, while others have not yet been evaluated sufficiently to decide on when and where to use them.
In this module we will briefly discuss the main techniques for detecting MTB. This implies examining not only test characteristics such as sensitivity and specificity, but also other factors such as technical requirements and costs.
The diagram below illustrates the various characteristics used to describe a diagnostic test.
FP = false positives of the test
FN = false negatives of the test
This cross-table shows the usual way to calculate the different values from results that were obtained comparing a given test against a “gold standard,” which is believed to indicate the total actually sick (“Disease present”) and the total not sick (“Disease absent”). In TB research, the gold standard will usually be culture. For microscopy rechecking quality control, for instance, it will be the results of the controllers.
Sensitivity and specificity are the basic characteristics, inherent to the technique but independent of the population in which it is used. Predictive values do take into account not only technique, but also the population in which it is used via the “prevalence” parameter. Prevalence indicates the frequency of the disease and will be different for different populations. With high prevalence, sensitivity needs to be high to reach a good negative predictive value (NPV). With low prevalence, so when the disease is rare, specificity needs to be very high, otherwise the positive predictive value (PPV) of a test will be poor. This is illustrated in the next diagram, showing the outcome of the same test (same hypothetical sensitivity and specificity) applied in populations with highly different prevalence of HIV seropositivity. PPV as well as NPV are dramatically different. In the first situation, a negative result still leaves about one chance in four that the patient is seropositive; in the second, there is less than one percent chance that a positive result truly indicates seropositivity, despite a seemingly high specificity.
The performance of various laboratory methods for detecting MTB is largely dependent on the numbers of TB bacilli or their products present in the samples. All tests will score better on specimens that are rich in bacilli, but only the most sensitive ones will also detect MTB in paucibacillary disease. As discussed earlier, the lungs of patients with infectious disease harbor many bacilli, and in high-prevalence areas these are also the most common type of patients. The curve below shows what this means for some tests in terms of proportions of patients that can be detected. AFB-microscopy needs minimally +/-5000 AFB per ml of sputum to yield a consistently positive result, and this is the case for most patients who present because of symptoms. This also shows that a distinct difference exists in sensitivity between excellent and poor AFB-microscopy. Culture as well as PCR can detect as few as 100 TB bacilli per ml, but this represents fewer patients in low-income countries. X-Ray is shown for comparison; it can in principle detect patients who do not excrete any TB bacilli at all.
Review of main lab methods
Roughly, the various tests we use can be classified as tests for detecting whole bacteria, or as those that detect compounds or products of the bacteria, and those that detect changes in the patient’s immunologic response to TB bacilli (serology).
1. Detection of whole bacteria
· microscopy for AFB
This will be discussed in detail in a separate chapter.
· culture of mycobacteria
Culture remains the gold standard in mycobacteriology because of its high sensitivity as well as specificity. Sensitivity reaches a minimum of about 100 bacilli per ml of sputum. In high-prevalence countries this may correspond to 80-90% of patients presenting because of symptoms. Sensitivity for cultures seems to be lower in AIDS patients with advanced immune deficiency, where fewer TB bacilli are present in sputum. Sensitivity will also be affected by technical factors, such as centrifugation and decontamination efficiency. In terms of specificity, culture has the big advantage by allowing differentiation between MTB and other mycobacteria, but this is less important in TB high-burden countries. On the other hand, specificity can suffer with careless technique. Transfer of TB-bacilli from positive samples may occur more frequently than when using microscopy. Specificity (assuming properly executed culture technique) will be around 99%, but in practice it will regularly be less.
The main disadvantage of culture is not the need for more sophisticated resources and more qualified technicians or higher cost, but its slowness. This is certainly so with the classical egg- or agar-based media (Löwenstein-Jensen, Ogawa, Middlebrook), for which a positive result requires on the average 3 weeks. The commercial liquid systems (BACTEC, MGIT) may reduce this time by 50% or more, but they are more costly and place higher demands on equipment, so that they cannot be routinely used in resource-poor countries.
The diagnostic delay of culture, together with the presence of advanced disease in many cases at presentation and the high index of suspicion among clinicians in countries with a high prevalence of TB, all work to reduce the usefulness of culture under these conditions. It has been shown that, under these circumstances, three smear examinations yield about the same as one culture. In addition, physicians will not wait for the results of culture to initiate TB treatment on other evidence. Moreover, repeating AFB smears after a few weeks in case symptoms persist, as is generally recommended, may give the same information as culture.
The conclusion may be that establishing culture facilities outside reference laboratories should not be a priority iational programs until it becomes clear that control of the disease is well under way and resources permit. Often these conditions will coincide, with earlier patient presentation because of economical improvement, and setting up culture facilities will automatically be part of the technological progress in general.
For reference laboratories in high-burden countries, culture will mainly serve as a first step in drug susceptibility testing (DST). DST itself will be reserved to track drug resistance. In these laboratories, culture may also enhance research.
2. Detection of compounds or products of the bacteria
· PCR-based genetic tests
Detection is based on multiplicatioot of whole bacilli, as in culture, but of their genetic material, chromosomal DNA or ribosomal RNA. Provided all ingredients are present in the reaction tube, this will only take place when the target genetic sequences to which the added primers can bind are found in the sample. Specificity of the test will thus depend on the use of correct primers, using sequences typical for MTB or MTB complex. In principle, from one target sequence, of one bacillus, the reaction can produce millions of copies and thus yield a positive result.
In practice, however, sensitivity is of the same order as that of culture or about 100 bacilli, due to the limited amount of sample that can be used and sometimes also due to the interference of reaction-inhibiting substances. Specificity of PCR is probably also similar to that of culture, but this needs further evaluation. Extremely careful technique is needed. Carry-over of DNA is even more likely to happen than that of whole bacteria so that early studies found up to 50% of positive results to be false. This places high demands on skills of the technician, as well as requiring special equipment and infrastructure (i.e. separate rooms).
The main advantage of PCR-based techniques is their speed; in principle, only 1-2 days are needed. This is true for diagnosis of TB, and even more so for applications such as diagnosis of drug resistance (mainly rifampicin) and species identification using probes.
The main disadvantage of PCR-based tests is their extremely high cost, especially when more convenient and more sensitive commercial test kits are available. Even in rich countries this has restricted their use, for instance, to determining the species present in smear-positive disease (FDA approval). This restricted use may also reduce the speed of the results, since it may not be possible to schedule PCR-runs daily.
For resource-poor countries, detection of TB using PCR seems unrealistic.
· Chromatography
Various techniques have been described using high-performance liquid chromatography (HPLC) or gas-liquid chromatography (GLC). Detection targets substances from the cell-wall such as mycolic acids, or metabolic products such as tuberculostearic acid. Results have been extremely good in terms of sensitivity and specificity as well as speed.
Nevertheless, these techniques seem to be used rarely in routine practice. The main reason for this may be the expense of the equipment, which has no other applications in the bacteriology laboratory.
· Antigen detection
See further, serology.
3. Serology
Antigen detection, antibody detection, detection of immune complexes or even immune-detection of complete bacterial cells, all have been described with many variations. The simplicity, ease and speed of these methods are attractive. A really good immunologic test could be applied by almost anybody and almost anywhere, and yield a result while the patient is waiting. For this reason, the search for such a test has been continuous since the time of Koch, with a re-intensification because of new discoveries such as monoclonal antibodies or recombinant peptides and perhaps now the deciphering of the MTB genome. New tests are continuously being introduced by scientists as well as commercial companies, always with big promises. So far, all of them have been disappointing.
The main problems seem to be that the antibody response to various TB antigens is highly variable between patients; it is very difficult to find a highly specific antigen as well. This results in problems of sensitivity as well as specificity, especially with easy-to-use formats such as latex-agglutination or immune-chromatographic (dot) tests. Typically, sensitivity is comparable to that of AFB-microscopy, and clearly better also in smear-positive cases. At the same time, however, specificity remains well under that of microscopy. At best it reaches about 95%. While this may seem high, it will lead to about 50% of false positives in all but high-prevalence regions. Better results are obtained with more complicated techniques, such as sandwich ELISA, but they are not useful in routine practice. On the other hand, far poorer results seem to be obtained in HIV positives. For instance a field evaluation of MYCODOT test in
To conclude, we do not yet have a serological test which is good enough, and especially not to detect the cases where microscopy remains deficient (HIV positive, children, EPTB). Considering experiences hitherto, claims in this regard by the manufacturers should be considered as publicity until field evaluation has proven their true value.
A note oon-laboratory methods for TB diagnosis
Clinical diagnosis of TB is not reliable at all, because there is not a single specific symptom or sign. In adults, the clinical picture will be used for selecting suspects who will be examined using more specific methods, especially AFB-microscopy. In children and also in some types of EPTB, the history and clinical signs will be given more importance, mainly because most or all diagnostic methods are less efficient.
X-Ray diagnosis of PTB is popular with physicians everywhere in the world, thanks to its speed, simplicity and ease of use when equipment is available, and possibly also because the physician sees it as his tool which he understands better. It is true that X-Ray has a high sensitivity, and it can detect TB in patients who do not excrete any bacilli.
We have seen that these are a small fraction of cases only in most high-prevalence countries, possibly more important where HIV is highly present, and that their prognosis is rather good with frequent self-healing. In addition, it has also been found that X-Ray will fail to diagnose about 10% of smear-positives under routine conditions.
The main objection against this method stems from its lack of specificity. This was shown long ago in several studies by IUATLD and others, where even specialist radiologists and chest physicians with long experience made at least 20% false-positives. In a control program, X-Ray will mainly be used by less experienced doctors, and regularly the radiographs are technically far from perfect. Experience has shown that its generalized use will then lead to 50-100% of over-diagnoses. This means a big waste of resources, with attention often being focused on old, inactive cases with persisting X-Ray lesions rather than on the active transmitters of the disease. Besides the greater expense and the unavailability of equipment in the least developed countries, this is the main reason for the objection of control programs against reliance on X-Ray to diagnose PTB.
Thus, in the control strategy, X-Ray for PTB diagnosis has been reserved for the second line, after AFB-smears have been found consistently negative. Its value will be greater for diagnosis of PTB in children and for some types of EPTB.
Mantoux testing using tuberculin, a protein extract from TB bacilli, is also often misused for TB diagnosis. The problem is that the test will be positive after any contact with TB or also after vaccination with BCG, in the absence of active disease. Thus, most adults in high-burden countries will test positive without showing any signs of the disease. Besides, there are many reasons why a Mantoux test can be false negative, and contact with environmental mycobacteria may cause doubtful reactions. Since the test always needs careful interpretation, it will never provide absolute proof of the disease.
Mantoux testing is thus not recommended for routine TB diagnosis, except in the case of children. It will then deliver only one of the arguments leading to a diagnosis when considered together with other arguments.
Methods of the X-ray diagnostics of tuberculosis of respiration organs. Methodical of interpretation roentgenograms of lungs and description pathological shadows
Roentgenologic examination is one of the main methods of diagnostics of tuberculosis and unspecific respiratory diseases. The following methods of roentgenologic diagnostics are used: roentgenoscopy, roentgenography, fluorography, tomography, computer tomography, target roentgenography, bronchography, fistulography, angiopulmography and bronchial arteriography, pleurography, kymography and polygraphy.
Roentgenoscopy is performed in various positions of a patient, at various respiration phases that allows to study the function of the diaphragm, heart pulsation, to choose the optimum spot for the puncture as well as prior to a target roentgenography, at performing bronchography, fistulography, angiopulmography etc.
In general, nowadays, lung roentgenoscopy is rarely done, more often by means of apparatus with electron-optical transformer. First of all an examining roentgenoscopy is done, during which the chest form is defined, transparence and the width of the lung fields, localization and the sizes of the shade of the mediastinum and the heart, mobility of the cupolas of the diaphragm and the rib front sections. After the examining roentgenoscopy the screen field is narrowed by the diaphragm and a more detailed examination of the lung tissue structure and pathologic changes is done.
Roentgenography allows to discover and fix on a film such morphological lungs structures, which are not visible at roentgenoscopia, to keep roentgenograms, to compare them in dynamics; and the most important is the fact, that radiation doze of a patient is much less, than at roentgenoscopy.
The disadvantage of the roentgenography is its statics, that doesn’t allow to judge about the organ function. However, the implication of the serial roentgenography and roentgenocinematography considerably level that shortcoming.
Normally the left lung is narrower and longer than the right one, mediastinum organs are localized between medial ends of clavicles at the background of the shadow of the sternum and the spine.
In the right lung there are 3 lobes (upper, middle and lower), in the left one – 2 (upper and lower). The lobes (upper and lower) are divided by the interlobular splits. Slanting interlobular split comes equally in the right and left lungs: from the level of the 4th thoracal vertebra sidelong down and forward to the cross with the 7th rib. On the right the horizontal split, that comes from the level of junction of the 4th rib and the sternum to the cross with the slanting interlobular split, divides the upper and middle lobes. Each lung has 10 segments. But sometimes there can be oly 9 segments in the left lung .
Segments of the right lung: 1-upper, 2-rear, 3-anterior, 4-exterior, 5-interior, 6-upper of the lower part, 7-inferointerior, 8-inferoanterior, 9-inferoexterior, 10-inferoposterior.
Segments of the left lung: 1-uper, 2-rear, 3-anterior, 4-upper-uvular, 5-lower-uular, 6-upper of the lower part, 8-inferoanterior, 9-inferoexterior, 10-inferoposterior.
The tuberculosis process is most often localized in the 1st, 2nd and 6th, sometimes in the forvard and basal segments. To define the localization of the process more precisely the roentgenograme in the lateral proection has to be done.
Lungs roots. The roots of the lungs are localized in the medial parts of the lungs, next to the heart shadow along two intercostals from the 3d rib down, gradually shifting the lungs picture.
Anatomic substratum of roots – large arterial and venous vessels, bronchi, groups of lymph nodes, connective tissue with lymphatic vessels and nervous trunks. Roentgenologically three parts are distinguished in the root: The head, the body and the tail. The head of the root is formed by the arcs shadows of main branches of the pulmonary artery and is localized at the level of the 3d rib and the 3d intercostal. The body of the root is formed by the shadows of the descending part of the pulmonary artery trunk and other vessels. The lower tail portion is formed by the shadows of lower veins and shifts the lung picture of lower lung portions.
The lungs picture is caused by the branches of pulmonary artery and veins vessels, that’s why it is also called vascular. During various pathological processes in the lungs, the picture may be intensified and indistinct. Sometimes a large vessel, having a transversal position, may form a shadow of round form resembling a fire. To specify the character of that shadow, the examination of the patient in various projections should be made.
The main roentgenologic shadows at lung tuberculosis are nidus (diameter to 1 сm), infiltrative (diameter over
A shadow in diameter of over
Before the analysis of the roentgenogram, the quality of its technical performance should be estimated. That should be done in the definite consequence: the completeness of the examined object scope (the whole thorax should be depicted on the roentgenogram – from the apex up to the phrenicocostal sinus); the patient’s position during the roentgenogram execution ( at the proper patient’s position, the distance between the medial edges of the clavicles and the spines of the 3d dorsal vertebrae are located symmetrically, scapulae shadows are depicted outward beyond the lungs margins; preciseness and contrastness (“preciseness and contrastness” assume nice outlining of every roentgenogram detail with different shades); and, at last, “strictness” (at optimal strictness of a roentgenogram, 3-4 upper dorsal vertebrae are clearly visible) of the roentgenogram.
Inspection roentgenography is carried out in the straight (right) (front and back), lateral and oblique projections. To define more accurately the localization and the character of the pathological process, a roentgenogram in a lateral projection is used.
The target roentgenography is done on a limited lung strip and in such a position of a patient as to get the most optimum picture of pathological changes, concealed behind the chest bone formations.
Tomography is the layer examination of a certain organ, in particular, the lungs. It allows to study in detail the structure of a pathologic formation at a respective optimum depth, chosen on the basis of the results of lateral roentgenography or roentgenoscopy .
Computer tomography is based on mathematical analysis of the intensity of absorption of the X-rays by tissues of various compactness and their transformation into the scheme, which reflects the pattern of diametrical layers of a human body on different levels (fig 4).
Fig.4 Computer tomography
Computer tomography allows to make more precise the localization and the spread of the pathologic process of lungs and mediastinum, reveal minute changes in pleura, in intrathoracic lymphatic nodes (fig 5).
Fig.5 Comruter tomograma patient with pulmonary TB
Fluorography(fig.6) is the principal method of mass examination of population, with big productive capacity and high informativeness it being done in various projections.
Fig.6 Fluorograma
However, the radiation dose of a person under examination is somewhat higher than that at roentgenography; that is why children undergo inspection roentgenography.
Bronchography is applied for examining the bronchial tree, for revealing bronchoectases, their number and form, as well as for revealing cavities. The procedure is made on an empty stomach, predominantly at the local anaesthesia, after which a contrast material (propiliodon, sulphoiodlipol etc.) is introduced through the catheter under the control of roentgenoscopy and roentgenography in two projections is done (Fig.7).
Fig.7 Bronchography
Fistulography. The method is applied for examining patients with various thoracic fistulas (thoracic and thoracobronchial). A contrast material (iodinelipol, propiliodon oil and water solutions) are introduced into the fistula and roentgenograms iecessary projections are performed.
Pleurography is predominantly performed to patients with pleural empyema to make its limits more precise. First the empyema contents is aspirated, then roentgen contrast material is introduced into the cavity (propiliodon, urographine, verographine) and roentgenograms in several projections are performed.
Angiopulmonography and bronchial arteriography are roentgenocontrasting methods of examining lung vessels of the small (angiopulmonography) and the large (bronchial arteriography) circles of blood circulation. Angiopulmonography: after catheterizing of the heart right sections and the lung artery under roentgenologic control a contrast material is introduced and a series of roentgenograms are performed. The aim of the examination is the diagnostics of thrombosis, the lung artery emboly as well as the study of pneumofibrosis degree.
Bronchial arteriography is catheterization, contrasting and roentgenography of bronchial arteries and their branches. The main indications are repeated lung haemorrhages and haemoptysis from the unknown source.
Kymography and polygraphy are applied for defining the mobility of the diaphragm and the heart.
Ultrasound examination (USE). At the respiration organs illnesses an ultrasound is applied, chiefly, for the examination of pleura, the function of the right ventricle of the heart and the pressure in the lung artery. USE is not applied for lung examination in so far as the filling of the lungs with air distorts the injures contours. The ultrasound method is applied for making pleura illnesses more precise, especially for the differentiation of a fluid and condensed (compact) elements.
Ultrasound examination, in particular, bimeasured echocardiography is applied to control the right ventricle index and the thickness of the fore-wall of the right ventricle, to define the time interval between closing the right auriculoventricular valve and opening the valve of the lung trunk. The data obtained show the degree of the correlation between hemodynamics and the parametres of the lung function.
Magneto-resonance examination. The method is applied for examining patients as it provides a sufficient contrast between fat tissue of the mediastinum, compact formations and vessel structures, allowing to indentify injures without intravenous introduction of a contrast material. The faults of the method: impossibility to define calcification, insufficient information about lung parenchyma.
TUBERCULINODIAGNOSTICS
Tuberculin testings are a specific diagnostic test, based on tuberculin property to cause in a human body, sensibilized by MBT, inflammatory reactions of dilatory type. They are used for mass examination of children and teenagers for tuberculosis, as well as for diagnostics, differential TB-diagnostics and the definition of the process activity.
It was Robert Koch who obtained tuberculin for the first time (1890) which was later named old Koch’s tuberculin (Alt Tuberculin Koch – ATK) (fig. 6). It is manufactured in ampules as 100 % solution and is a liquid of dark-brown colour, which contains, in addition to specific active substances (tuberculoproteins), products of MBT vitality, elements of their cells and the medium on which they grew.
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Fig. 8. Old Tuberculin Koch (АТК). |
In
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Fig. 9. Dry rectified tuberculin (50000 ТU), the solvent is isotonic solution of sodium chloride – 1ml with the addition of 0,25 % carbolic acid. |
In Ukraine PPD is manufactured as a solution ready for use, the sterility of which is guaranteed by the presence in it of 0,01 % chinozol. The solution is packed in ampules of 3 ml (30 doses) or in bottles of 5 ml (50 doses). Each dose – 0,1 ml contains 2 TU. According to the WHO standard, 1 TU contains 0,00006 mg of PPD-L or 0,00002 of PPD-S.
Tuberculin is an incomplete antigen and therefore it does not cause the formation of antibodies, but it calls forth a reaction in a sensibilized organism with a complete antigen (MBT, vaccine strain of BCG).
Depending on the mode of tuberculin introduction, cutaneous Pierquet test (Pierquet, 1907), intracutaneous – Mantoux (Mantoux, 1910; Mendel F., 1909) and subcutaneous Koch test (Koch, 1890).
Mantoux test is applied at mass examinations for tuberculosis, while Koch test is applied under the conditions of a clinic with a view to diagnose and define the activity of tuberculosis process. Pierquet test has lost its diagnostic value and is extremely rarely applied nowadays.
In the basis of an organism’s reaction to tuberculin is an immunologic reaction of increased sensitivity and slow type (ISST). After MBT infecting (vaccination or revaccination) hypersensitiveness to tuberculin appears in about 6-8 weeks. The reaction intensity to tuberculin depends on the degree of the organism specific sensibilization and its reactivity as well as on various endogenic and exogenic factors (fig. 10).
Mass and individual tuberculinization is distinguished.
The aim of mass tuberculinization:
1. Early tuberculosis revealing,
2. Revealing persons with an increased risk of tuberculosis illness,
3. Contingent selection for BCG revaccination,
4. Determination of infestation index of MBT population,
5. Differential diagnostics between infectious and pastvaccinal allergy.
Fig. 10. Positive Mantoux test.
Mantoux testing of 2 TU of purified tuberculin in standard solution is applied in solving these tasks.
The results of Mantoux testing, which are estimated in 72 hours, may be as follows:
1. Negative – absence of an infiltrate or only a sign after an injection to
2. Doubtful – a 2-
3. Positive – a
4. Hyperergy – with children and teenagers an infiltrate of
At the needleless method the size of the papule is
With a view of early revealing of tuberculosis, the intensity of tuberculin reaction or tuberculosis intoxication, the Mantoux test with 2 TU is made to all children and teenagers starting from 12-months age, is annually repeated irrespective of the previous result. On twin years the test is made on the right, on add ones – on the left forearm, at the same time (preferably in autumn).
Contraindications for mass Mantoux test are skin diseases, acute and chronic infectious diseases (not less than two months after clinical symptoms disappearance), allergic states, bronchial asthma, idiosyncrasy with marked skin manifestation, rheumatism in acute and subacute phases, epilepsy. Mantoux test is not performed in children collective bodies during infections quarantine. By the way, the interval between various prophylactic inoculations and Mantoux test should be not less than a month.
The following information should be taken into account for differential diagnostics of infectious and postvaccinal allergy:
2. Whether BCG vaccine innoculation was done, the term of the last vaccination;
3. Tuberculin reaction intensity during the last examination and in previous years.
The most distinctive features for postvaccinal allergy are: negative, doubtful or positive reactions with the infiltrate size of 5-
Infectious allergy: first positive reaction (
Table
Characteristics of infectious and postvaccinal
tuberculin reactions
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Postvaccinal allergy |
Infectious allergy |
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1. Negative, doubtful or positive reactions with 5- 2. Rarely 12- 3. Maximum expressed reaction in 1-1,5 years after vaccination (rarely in 2 years) onward it gradually decreases. |
1. First positive reaction ( 2. Stable preservation during a few years of tuberculin reaction with an infiltrate size of 3. Increase of intensivity of previously doubtful or positive tuberculin reactions for 4. Hyperergic reactions |
A contact with a tuberculosis patient, combining first registered positive Mantoux test with the availability of clinical illness symptoms testifies of the primary MBT infestation (intensivity of tuberculin reaction), tuberculosis intoxication or even a local specific process.
Tuberculin intensifier is the appearance of first positive tuberculin reaction after a negative one within a year or its increase in persons vaccinated with BCG vaccine at
All children with tuberculin reactions intensification should be thoroughly examined for tuberculosis as well as children and teenagers with hyperergic tuberculin reactions infestated long ago or at tuberculin sensitivity increase (
Individual tuberculin diagnostics. Depending on the indications at individual tuberculin diagnostics Mantoux test with 2 TU is applied, as well as with various tuberculin doses. Generally, Mantoux test with 2 TU is of importance for children and teenagers; for adults, in separate occasions, hyperergic results of Mantoux test testify of the active tuberculosis, while the negative ones of tuberculosis absence, therefore sometimes the necessity arises to apply Koch test (10-100 TU). A negative reaction to 100 TU of tuberculin with the probability of 97-98 % allows to exclude tuberculosis infestation. Koch’s testing is done with a view of diagnostics and differential diagnostics of tuberculosis, the definition of the activity of tuberculosis process. Before the Koch testing, Mantoux test with 2 TU is done for ascertaining the tuberculin titre. After this near the lower angle of a shoulder-blade or in the upper third of the outer surface of the shoulder, after rubbing the skin with 700 ethylic alcohol, tuberculin is injected subcutaneously in the dose from 20 to 100 TU. Two or three days before the procedure the clinical blood analysis is done every day, the intake of lavage waters of bronchi for MBT, measuring the body temperature every 4 hours; a day prior to Koch’s test the protein fractions of the blood serum are defined. In 24-48-72 hours after subcutaneous tuberculin injection the examinations analogous to those before the tuberculin injection, are done. Roentgenological examination before and after Koch’s testing (in 48 hours and on the 7th day) is performed depending on the process localization.
Koch test results are evaluated in 24, 48 and 72 hours, based on the results of local, nidal and general reaction. The local reaction is supposed to be positive at the formation of subcutaneous infiltrate of the
1 case detection
The detection of TB cases requires that affected individuals are aware of
their symptoms, have access to health facilities and are evaluated by health
workers (doctors, nurses, medical assistants, clinical offcers) who recognize
the symptoms of TB. Health workers must have access to a reliable laboratory
and ensure that the necessary specimens are collected for examination. This is
a complex set of activities and behaviours, and failure at any stage can cause
delays in diagnosis or misdiagnoses.
The most common symptom of pulmonary TB is a persistent, productive cough,
often accompanied by other nonspecifc symptoms. Although the presence of
a cough for 2–3 weeks is nonspecifc, traditionally having a cough of this dura-
tion has served as the criterion for defning suspected TB and is used in most
national and international guidelines.
The following symptoms of pulmonary TB may accompany cough and sputum
production:
• respiratory symptoms: shortness of breath, chest and back pains, haemop-
tysis;
• constitutional symptoms: loss of appetite, weight loss, fever, night sweats,
fatigue.
Symptoms of extrapulmonary TB are related to specifc extrapulmonary sites,
such as lymph nodes, pleura, larynx, meninges, genitourinary and intestinal
tracts, bone, spinal cord, eye and skin.
Sputum smear microscopy. Sp u t um s p e c imes s h o u l d b e o b t a ie d f o r mi c r o s c o p i c
examination from all patients suspected of having pulmonary TB. microbiological
diagnosis is confrmed by culturing M. tuberculosis (or, under appropriate cir-
cumstances, by identifying specifc nucleic acid sequences in a clinical specimen)
from any suspected site of disease. However, in many settings where resources
are limited, neither culture nor rapid amplifcation methods are currently availa-
ble or feasible. In such circumstances, the diagnosis of TB may also be confrmed
by the presence of acid-fast bacilli (AfB) in sputum smear examination. repeated
sputum smear microscopy may diagnose pulmonary TB in up to two-thirds of
active cases.
Iearly all clinical circumstances in settings of high TB prevalence, identifca-
tion of AfB by microscopic examination is highly specifc for the M. tuberculosis
complex. Sputum smear microscopy is the most rapid method for determining
whether a person has TB; it identifes people who are at greatest risk of dying
from the disease and the most likely transmitters of infection.
Sputum specimens. The optimum number of sputum specimens to establish a
diagnosis has been evaluated. The frst specimen was found positive in 83–87%
of all patients in whom AfB are ultimately detected; the second specimen was
positive in an additional 10–12% and the third specimen in a further 3–5%.
On this basis, WHO recommends the microscopic examination of two sputum
specimens (formerly three).
1
Because the yield of AfB appears to be greatest
from early morning (overnight) specimens, WHO further recommends that at
least one specimen should be obtained from an early morning collection.
Sputum collection procedures. The procedures for collecting sputum involve
the production of droplets that are highly infectious if the patient has untreated
pulmonary TB. Sputum collection should therefore be organized in areas with
good ventilation or, if not available, outside the building (see chapter 6).
Sputum smear specimens should be examined by microscopy immediately but
no later than 5 to 7 days after they have been collected. A health unit with-
out adequate facilities for collecting and transporting sputum should refer the
patient to the nearest health unit able to collect sputum, or direct the patient
to a microscopy laboratory.
national TB guidelines should include all the details of what health workers
should do before, during and after the collection of sputum. Attention should
be paid to the characteristics of sputum containers, precautions for health
workers, labelling, identifcation and recording of patients’ addresses.
Diagnosis of smear-negative tuberculosis. for smear-negative and extrapulmo-
nary TB, a diagnosis by a clinician specially trained in TB may be required as
well as radiographic examination. As no chest radiographic pattern is abso-
lutely specifc for pulmonary TB, the diagnosis of smear-negative TB is always
presumptive and should be based on other clinical and epidemiological infor-
mation, including failure to respond to a course of broad-spectrum antibiotics
and exclusion of other pathology. reliance on chest radiography as the only
diagnostic test for TB results in either overdiagnosis of TB or missed diagnoses
of TB and other diseases and is therefore not recommended. radiographic
examination, however, is most useful when applied as part of a systematic
approach to evaluate patients whose symptoms and/or fndings suggest TB but
whose sputum smears are negative. fluoroscopy results are not acceptable as
documented evidence of pulmonary TB.
Pregnancy. case-detection methods in pregnancy should exclude radiographic
examination, particularly in the frst trimester.
Culture. While sputum smear microscopy is the frst bacteriological diagnostic
test of choice where adequate, quality-assured laboratory facilities are avail-
able, the evaluation of patients with negative sputum smears should also
include culture. culture adds extra cost and complexity but greatly increases
the sensitivity and specifcity of diagnosis, resulting in better case detection.
Although the results of culture may not be available until after a decision to
begin treatment has been made, treatment may be stopped subsequently if
cultures from a reliable laboratory are negative and if the patient has not
responded clinically to treatment and the clinician has sought other evidence
in pursuing the differential diagnosis.
figure 1.1 presents an illustrative approach to the diagnosis of pulmonary TB in
settings with a low prevalence of HIV infection. diagnostic algorithms for high
HIV-prevalent settings and for seriously ill patients are provided in section 1.3.
Extrapulmonary tuberculosis. extrapulmonary TB (without associated lung
involvement) accounts for 15–20% of TB in populations with a low prevalence of
HIV infection. In populations with a high prevalence of HIV infection, the propor-
tion of cases with extrapulmonary TB is higher. Because appropriate specimens
may be diffcult to obtain from some of these sites, bacteriological confrmation
of extrapulmonary TB is often more diffcult than for pulmonary TB. relatively
few M. tuberculosis organisms are present in extrapulmonary sites, and identi-
fcation of AfB by microscopy in specimens from these sites is infrequent. for
example, microscopic examination of pleural fuid in tuberculous pleuritis and
tuberculous meningitis detects AfB in only about 5–10% of cases.
given the low yield of microscopy, both culture and histopathological examina-
tion of tissue specimens, such as those that may be obtained by needle biopsy
of lymph nodes, are important diagnostic tests for extrapulmonary TB.
1.1 Case defnitions of tuberculosis
A diagnosis of TB should be followed by specifcation of the type of TB, i.e.
the case defnition, which is necessary for prescribing treatment according to
standardized regimens, for patient registration and reporting, for cohort analy-
sis of treatment outcomes and for determining trends.
case defnitions for TB take into account the anatomical site of disease, the
bacteriological results, the severity of disease and the history of previous treat-
ment. Tables 1.1 and 1.2 present the defnitions of TB cases by site, bacteriologi-
cal status and history of previous treatment in adult patients. The defnition
of a sputum smear-positive case is the same for HIV-positive and HIV-negative
patients, i.e. requiring at least one positive smear in countries with a functional
system of external quality assurance (eQA).
1.1.1 Anatomical site of disease
The two main categories of TB by anatomical site of disease are: (i) pulmonary
TB, or disease affecting the lung parenchyma (the most common form of TB);
and (ii) extrapulmonary TB, or disease affecting sites including lymph nodes,
pleura, meninges, pericardia, peritoneum, spine, intestine, genitourinary tract,
larynx, bone and joints, and skin.
1.1.2 Bacteriological results
“Smear-positive” or “smear-negative” is the most useful bacteriological clas-
sifcation of pulmonary cases because it correlates with infectiousness. In set-
tings where culture facilities are available, the results of culture are included in
the bacteriological classifcation. Under most programmatic conditions – when
only microscopy laboratory services are available and when diagnostic criteria
are properly applied – smear-positive cases represent more than 65% of the
TABlE 1.1 cASe defInITIOnS BY SITe And BAcTerIOlOgIcAl STATUS In HIV-negATIVe
AdUlTS And fOr nOn-HIV preVAlenT SeTTIngS
Case classifcation Defnition
Pulmonary tuberculosis, One or more initial sputum smear examinations positive for
sputum smear-positive (PTB+) Acid-fast bacilli by microscopy
Pulmonary tuberculosis, A case of pulmonary tuberculosis who does not meet the above
sputum smear-negative (PTB–) defnition for smear-positive tuberculosis.
Note: In keeping with good clinical and public health practices,
diagnostic criteria should include:
1. At least two sputum specimens negative for acid-fast bacilli,
and
2. radiographic abnormalities consistent with active pulmonary
tuberculosis, and
3. no response to a course of broad-spectrum antibiotics, and
4. decision by a clinician to treat with a full course of anti-
tuberculosis chemotherapy.
This group includes patients whose sputum smears are
negative but whose culture is positive.
Extrapulmonary tuberculosis A patient with tuberculosis affecting organs other than the
lungs. diagnosis should be based on one culture-positive
specimen, or histological or strong clinical evidence consistent
with active extrapulmonary tuberculosis, followed by a decision
by a clinician to treat with a full course of anti-tuberculosis
chemotherapy.
TABlE 1.2 cATegOrY Of pATIenTS fOr regISTrATIOn On dIAgnOSIS
(BASed On HISTOrY Of preVIOUS TreATmenT)
Diagnostic/registration category Defnition
New A patient who has never had treatment for tuberculosis or
who has taken anti-tuberculosis drugs for less than one
month.
Re-treatment Relapse A patient previously treated for tuberculosis who has been
cases declared cured or treatment completed, and is diagnosed
with bacteriologically positive (at least one smear or
culture) tuberculosis.
Treatment A patient who is started on a re-treatment regimen after
after failure previous treatment has failed.
Treatment A patient who returns to treatment with positive
after default bacteriology, following interruption of treatment for two
months or more.
Transfer in A patient who has been transferred from another
tuberculosis register to continue treatment in a different
register area.
Other All cases who do not ft the above defnitions. This
group includes patients who are sputum smear-positive
at the end of a re-treatment regimen (previously defned
as chronic cases) and who may be resistant to the
frst-line drugs.
Note: Smear-negative pulmonary and extrapulmonary cases may also be relapses, failures or
other cases. Such diagnoses should be supported by pathological or bacteriological evidence.
total number of cases of pulmonary TB in adults, and 50% or more of all TB
cases (although those proportions may be altered in settings with high preva-
lence of HIV infection).
A patient with both pulmonary and extrapulmonary TB is classifed as a case
of pulmonary TB.
1.1.3 Severity of disease
Bacillary load, extent of disease and anatomical site are factors that deter-
mine the severity of TB disease, and consequently its appropriate treatment.
A case of pulmonary TB is classifed as severe if parenchymal involvement is
extensive. miliary disseminated TB is also considered severe. Involvement of an
anatomical site results in classifcation as severe disease if there is a signifcant
acute threat to life (e.g. pericardial TB), a risk of subsequent severe handicap
(e.g. spinal TB) or both (e.g. meningeal TB).
The following forms of extrapulmonary TB are classifed as severe: meningeal,
pericardial, peritoneal, bilateral or extensive pleural effusion, spinal, intestinal
and genitourinary. TB of the lymph nodes, unilateral pleural effusion, bone
(excluding spine), peripheral joint and skin is classifed as less severe.
1.2 Case detection of drug-resistant tuberculosis
programmatic strategies for the management of drug-resistant TB aim to iden-
tify patients and initiate adequate treatment for drug-resistant cases in a timely
manner. prompt identifcation and initiation of adequate treatment gives a bet-
ter chance of cure for patients, provides the best infection control measure, and
prevents the acquisition of further resistance and progression to a chronic state
of permanent lung damage.
WHO recommends that programmes have population-representative data of
drug resistance surveillance (drS) for new patients, for the different categories
of re-treatment patients (failure after category I, failure after re-treatment,
default and relapse) and for other high-risk groups (see chapter 2). designing
an effective case-fnding strategy depends on this information. Availability of
drS data for the different groups also enables calculation of the number of
patients who should enter the programme; this in turn greatly facilitates pro-
gramme planning and drug procurement (see also chapter 14).
Some programmes may not have suffcient laboratory capacity to provide drug
susceptibility testing (dST) of all patients. Where targeted dST surveys identify
a risk group or groups of patients with a high proportion of mdr-TB (which may
exceed 80%), the use of category IV regimens in all patients in that group is
justifed.
The three risk groups commonly considered for direct enrolment for a category
IV regimen are:
• category II failures (chronic TB cases);
• TB patients who are close contacts of mdr-TB cases;
• category I failures who received a full
course of treatment.
The proportion of mdr-TB in these
three groups may vary considerably. It
is therefore important to confrm mdr-
TB through the use of dST (to, at least,
isoniazid and rifampicin) for all patients
who start a category IV regimen.
In most settings, other groups are
unlikely to have rates of mdr-TB suff-
ciently high to warrant entry into a drug-
resistant TB treatment regimen without
confrmation of mdr-TB by dST (Box
1.1).
DEFINITIONS OF MulTIDRuG-
RESISTANT TuBERCulOSIS AND
ExTENSIVEly DRuG-RESISTANT
TuBERCulOSIS
n MDR-TB. Tuberculosis with
resistance to, at least, isoniazid, and
rifampicin.
n xDR-TB. Tuberculosis with
resistance to, at least, isoniazid
and rifampicin and to any of the
fuoroquinolones and to one of the
following injectable drugs: amikacin,
capreomycin, kanamycin.
1.3 Case detection of tuberculosis and human immunodefciency virus
Important differences exist in the diagnosis of TB in HIV-prevalent settings
and in settings of low HIV prevalence. HIV alters the clinical pattern of TB and
complicates its diagnosis.
Infection with HIV increases the risk of progression of recent M. tuberculo-
sis infection and of reactivation of latent M. tuberculosis infection by 5–15%
annually, depending on the degree of immune defciency. It also increases the
rate of recurrence of TB, both relapse (reactivation of latent TB) and reinfec-
tion (newly acquired infection). HIV is responsible for a large increase in the
proportion of patients with smear-negative pulmonary and extrapulmonary TB.
These patients have inferior treatment outcomes, including excessive early
mortality, compared with HIV-positive, smear-positive pulmonary TB patients.
Tackling this problem requires rapid diagnosis of smear-negative pulmonary
and extrapulmonary TB in settings with high HIV prevalence.
Effect of HIV on TB. HIV infection causes reduced immune competence and the
consequent loss of ability to prevent the spread of the tubercle bacilli from
localized granulomas (due to a decline in the number of cd4+ T cells). rapid
progression from initial infection to TB disease may also occur in markedly
immunosuppressed patients. patients with active TB who are HIV-positive have
a higher risk of dying from TB than those without HIV.
In the early stages of HIV infection, before host immunity is signifcantly com-
promised, patients with TB have the typical symptoms of TB, and smear micro-
scopy is usually positive. With more advanced HIV infection and compromised
immune status, TB symptoms are atypical and the smear is ofteegative. pau-
cibacillary (scanty) smears are also more frequent in HIV-infected TB patients.
HIV-positive patients with smear-negative TB are more likely to die during or
before diagnosis than HIV-negative smear-positive patients.
Radiography. The use of chest radiography to diagnose pulmonary TB may be
compromised by poor flm quality, low specifcity and diffculties with interpre-
tation. HIV infection further diminishes the reliability of chest radiographs for
the diagnosis of pulmonary TB because the disease commonly presents with
an atypical pattern. furthermore, the chest radiograph may be normal in a
proportion of HIV-infected patients with sputum culture-positive TB (observed
in up to 14% of such cases). However, chest radiography remains an important
adjunct to the diagnosis of smear-negative pulmonary TB in people living with
HIV (plHIV).
Diagnostic algorithms. Algorithms for the diagnosis of TB in ambulatory patients
in HIV-prevalent settings and in seriously ill HIV-positive patients are provided
below (figures 1.2 and 1.3).
The diagnosis of smear-negative pulmonary TB is particularly diffcult among
HIV-positive patients, and use of the algorithm is therefore recommended.
The algorithm for HIV-negative patients (figure 1.1) includes treatment with a
course of broad-spectrum antibiotics to exclude infections other than TB, and
to improve the specifcity of the diagnosis.
The result of antibiotic treatment is not affected by HIV status. However, patients
with TB may lose their respiratory symptoms after a course of antibiotics.
The specifc aspects of TB diagnosis in HIV-prevalent settings are that:
• the clinical assessment of the seriousness of disease is taken into account;
• special efforts to avoid delay in establishing the diagnosis should be made;
• the use of antibiotics (for clinical reasons) is not a step in the diagnostic
process;
• all available investigations, such as chest radiography, culture of sputum
and specimen culture for cases of extrapulmonary TB, should be carried out
as soon as possible.
The Diagnosis of Tuberculosis
Daniel Brodie, MD, Neil W. Schluger, MD*
Division of Pulmonary, Allergy, and Critical Care Medicine, Columbia University Medical Center, 622 West 168th Street,
PH 8 East, Room 101, New York, NY 10032, USA
Tuberculosis is transmitted from person to per-
n by respiratory droplets. Although some people
evelop active tuberculosis disease after infection,
most all tuberculosis infections are asymptomatic
nd remain latent. Latent tuberculosis infection
TBI) itself progresses to active disease in approx-
mately 5% to 10% of infected persons. The rate of
ogression is much greater in immunocompromised
dividuals. The estimated 2 billion people living with
TBI represent a vast reservoir of potential cases of
berculosis around the world. This reservoir of LTBI
therefore a major barrier to the ultimate control and
imination of tuberculosis.
Strategies to combat tuberculosis in regions that
e resource-rich aim, first, to identify and treat per-
ns who have active disease; second, to find and
eat contacts of cases of active disease who develop
TBI, and, third, to screen high-risk populations and
eat LTBI [1]. Diagnosis and treatment of LTBI are
ucial in this effort. In most of the world, however,
sources are devoted exclusively to the highest pri-
ities of tuberculosis control: identification and treat-
ent of active disease [1]; for lack of resources, LTBI
neither diagnosed nor treated.
Diagnostic testing for both LTBI and active dis-
se has changed little during the last century. Be-
use of limitations in available tests, there has long
en a clear need for better diagnostic tests. LTBI,
ntil very recently, has been diagnosed exclusively by
e tuberculin skin test (TST). The TST is fraught
ith problems including relatively poor sensitivity
and specificity. Newer tests for LTBI offer the prom-
ise of greatly improved diagnostic accuracy.
Tools for the diagnosis of active disease include
clinical suspicion, response to treatment, chest radio-
graphs, staining for acid-fast bacilli (AFB), culture
for mycobacteria, and, more recently, nucleic acid
amplification (NAA) assays. AFB smears lack both
sensitivity and specificity, and culture is very slow to
produce results, limiting the ability to diagnose active
disease effectively. NAA assays and several other
experimental diagnostic tools can add significantly
to the active disease diagnostic armamentarium. The
suitability of newer diagnostic tests in a given popu-
lation varies according to the resources available to
pay for and implement those tests, however [2].
In resource-poor countries, where options are lim-
ited, current approaches, such as relying almost ex-
clusively on the sputum smear for the diagnosis of
active disease, leave a significant number of cases
undetected [3–6]. This approach may be the only
economically feasible strategy given the initial costs
involved in the widespread use of other diagnostic
modalities. Although smear-positive cases are the
most infectious, neglecting smear-negative disease
(approximately half of cases overall) increases the
morbidity and mortality of the disease in those pa-
tients and does not account for the significant burden
of transmission attributable to these smear-negative
cases (17% of all transmission in one study using
molecular epidemiology techniques) [6].Thein-
creased likelihood of smear-negative tuberculosis in
HIV patients, particularly those who have advanced
immunosuppression [7], makes this diagnostic
approach especially problematic, because the regions
most afflicted by tuberculosis are similarly inundated
with HIV infection.
* Corresponding author.
E-mail address: [email protected] (N.W. Schluger).
Meanwhile, in resource-rich countries, under-
diagnosis is less an issue than overdiagnosis with
its attendant costs (the production of specimens, the
surveillance of cultures—most of which will ulti-
mately be negative—use of isolation rooms, empiric
therapy for tuberculosis, and expensive or invasive
diagnostic testing) [8]. In part, the need is for more
rapid diagnosis, allowing for earlier treatment of
cases, decreased transmission of active disease, and
decreased expenditure of resources. There is also a
need for increased sensitivity of testing so that cases
do not go unrecognized, and for increased specificity
and negative predictive value to decrease the cost of
having a high suspicion for this disease.
An ideal test for active tuberculosis would
produce rapid results (available within 1 day), would
have high sensitivity and specificity, low cost, and
robustness (ability to provide reproducible results in
a variety of settings), would be highly automated
or easily performed without the need for excessive
sample preparation or technical expertise, and would
be able to provide drug-susceptibility data. Ideally,
such a test would also be able to distinguish between
LTBI and active disease. For LTBI, such a test would
distinguish true infection from bacille Calmette-
Guerin (BCG) vaccination and infection with non-
tuberculous mycobacteria (NTM). In cases of active
disease, it would be valuable to be able to determine
infectiousness, follow response to therapy, distinguish
Mycobacterium tuberculosis from NTM in AFB-
positive specimens and obtain drug-susceptibility
information. No test performs all these functions at
present, but several new tests are being used or are
currently under study that incorporate many of these
features and offer the possibility of improved diag-
nosis of LTBI and of active disease.
Tests for latent tuberculosis infection
The tuberculin skin test
Tuberculin, a broth culture filtrate of tubercle
bacilli, was first described in detail by Robert Koch
in
cure for tuberculosis [9]. Although its purported
curative properties proved unfounded, Koch observed
that subcutaneous inoculation of tuberculin led to
a characteristic febrile reaction in patients who had
tuberculosis but not in those who did not have
tuberculosis, giving rise to its use in the diagnosis of
the disease. The technique was refined over the next
2 decades so that cutaneous or intradermal inocu-
lation restricted the reaction to the skin. Subse-
quently, a standardized version of tuberculin, the
purified protein derivative (PPD), was introduced in
1934 [9]. In 1939, the batch of PPD known as PPD-S
was produced by Seibert and Glenn [3]. This batch
remains the international standard for PPD to this day.
In the early years of the TST, the assumption that
tuberculin reactions resulted solely from tuberculo-
sis infections went virtually unchallenged [9]. By the
mid-1930s, however, mounting evidence suggested
that tuberculin reactions might not be restricted to
such infections. In addition, investigators noted that if
the dose of PPD were increased enough, almost
everyone tested positive, including infants unlikely to
have been exposed to tuberculosis [9]. These findings
called into question the specificity of the TST, high-
lighting its limitations for the first time.
The current state of knowledge about the utility of
tuberculin skin testing derives in large measure from
a series of trials performed in epidemiologically well-
defined populations of persons who have known
Tuberculosis patients
Dose of tuberculin (mg)
Per cent reacting
Healthy children
100
80
60
40
20
0
10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100
5 TU PPD-S
Fig. 1. Cumulative frequency of reactors responding to increasing doses of tuberculin among healthy children and patients
with tuberculosis. TU, tuberculin units. (From Reider H. The epidemiologic basis of tuberculosis control.
tuberculosis disease, those at extremely low like-
lihood of having latent infection, and those likely
to be close contacts of persons who have active
tuberculosis. Reider [10] has described these trials
in detail.
The dosing of tuberculin for use in skin testing
was determined in studies such as one done in
in which skin testing was performed on tuberculosis
patients and a group of children in orphanages who
had little chance of tuberculosis exposure. At a dose
of 104
mg of tuberculin, a clear distinction could be
made between the two groups (Fig. 1). Refinements
in dosing and criteria for positivity were achieved by
using standardized preparations of PPD made by the
Statenseruminstitut in
groups of Eskimo children (a group that has a high
likelihood of latent infection acquired from close
contact with active cases and very little exposure to
environmental mycobacteria) and US Navy recruits
who have little chance of contact with active tuber-
culosis but have frequent exposure to environmental
mycobacteria (Fig. 2). Testing of 5440 tuberculosis
patients revealed a normal distribution of extent of
induration, with a mean of 16 to
Finally, a massive survey of more than 700,000 US
military recruits, of whom 400,000 had no known
contact with tuberculosis patients and 10,000 had
definite contacts, provided meaningful data on which
to base recommendations for interpretation of skin
tests that are still useful today (Fig. 4).
Although the TST has been in widespread use for
a century and is the only universally accepted test for
the diagnosis of LTBI, it suffers from significant
inherent limitations. To understand these limitations,
it is useful to review the mechanism of the TST.
Infection with M. tuberculosis results in a cell-
mediated immune response giving rise to sensitized
T lymphocytes (both CD4+
and CD8+
[11]) targeted
to M. tuberculosis antigens. Stimulation by M. tu-
berculosis antigens causes these T cells to release
interferon-gamma (IFN-g). The TST functions by
eliciting this response in previously sensitized indi-
viduals. In such individuals, an intradermal injection
of PPD evokes a delayed-type hypersensitivity re-
sponse mediated by sensitized T cells and results in
cutaneous induration. PPD, however, is a precipitate
of M. tuberculosis culture supernatant which contains
roughly 200 antigens, many of which are shared by
other mycobacteria including many NTM and
M. bovis BCG [12,13]. A response to PPD may sig-
nify infection with M. tuberculosis or, just as readily,
infection with NTM [14–18] or vaccination with
BCG [18–22]. This cross-reactivity seriously limits
the specificity of the TST in many populations [23].
Given that one quarter to one half of the burden
of tuberculosis in developed countries is found in
foreign-born immigrants from high-prevalence coun-
tries, and this population is made up precisely of
those who are likely to be BCG-vaccinated and to
have been exposed to NTM, the TST is least reliable
in those most ieed of screening. Specificity is a
major shortcoming of the TST. In addition, sensitiv-
ity of the TST may also be poorest in patients at high
risk for developing tuberculosis. Anergy caused by
an immunocompromised state (especially with HIV
infection or medication-induced immunosuppression)
may lead to false-negative results [24]. False-negative
results also may occur up to about 10 weeks after
infection with M. tuberculosis [25–27]. False nega-
tives, particularly in the HIV population where the
implications of active disease are most pressing
[3,28,29], greatly limit the utility of this test.
The exact sensitivity and specificity of the TST
for LTBI is impossible to know with certainty, given
the lack of a reference standard for diagnosis. In that
context, estimates of the global burden of LTBI are
especially problematic. Estimates indicate that the
problem is enormous, but these estimates are based
on the performance of the TST, and such estimates,
particularly in developing countries, are notoriously
unreliable [30,31]. Studies of the prevalence of LTBI
in
ranging from 9% [32] to more than 80% in various
populations [33]. A more accurate epidemiologic tool
would greatly facilitate a better estimation of the true
scope of the problem.
The TST is limited further by the subjectivity of
its interpretation [34], in particular, by problems with
interreader and intrareader reliability [25,35–37] and
digit preference [38,39]. Also, the existence of the
booster phenomenon [24,25,39–41], poor standardi-
zation of PPD preparations [31], and, logistically, the
need for a return visit to have the test read make the
TST a highly imperfect diagnostic tool. That it does
not distinguish between LTBI and active disease also
limits its usefulness.
Whether the extent of induration resulting from
tuberculin skin testing can predict the development of
tuberculosis in a linear (or at least dependent fashion)
has also been the subject of considand investigation. Recently, Horsburgh [42] has pro-
vided a well-reasoned and -supported data set that
gives guidance in this area.
Alternatives to the TST are lacking. Serologic
tests for the diagnosis of M. tuberculosis have been
disappointing [43,44]. Although an antibody re-
sponse to M. tuberculosis antigens occurs, there is
great individual variability in the number and type
of serologically reactive antibodies [44], making this
diagnostic tool too unreliable. Because no serologic
tests for tuberculosis are remotely good enough to be
used clinically at present, they are not discussed fur-
ther in this article.
Despite its many limitations, the TST by neces-
sity remains in widespread use. In 2000, the Centers
for Disease Control and Prevention (CDC), the
American Thoracic Society (ATS), and the Infectious
Disease Society of America (IDSA) issued updated
guidelines for the use of the TST in screening for
LTBI [24]. These guidelines stress that in general one
should not place a TST unless treatment would be
offered in the event of a positive test. In addition,
cut-off points of induration (5, 10, or
determining a positive test vary by the pretest risk
category into which a patient falls. This approach
may further decrease the specificity of the test, but
it increases the sensitivity for capturing those at
highest risk for developing active disease in the short
term. Continued focus on this century-old test high-
