Immunodiagnosis of tuberculosis: An update

Cytodiagnosis of tuberculosis using modified bleach method on lymph node aspirates

Background:

The conventional Ziehl–Neelsen (ZN) staining method for demonstration of acid-fast bacilli (AFB) by direct microscopy plays a key role in the diagnosis of tuberculosis. Its major disadvantage is low sensitivity.

Aims:

The present study was undertaken to emphasize the role of bleach concentration method over conventional ZN smear for detection of AFB in fine-needle aspiration (FNA) material of clinically suspected tuberculous lymphadenitis.

Settings and Design:

Tertiary care teaching hospital, cross-sectional design.

Materials and Methods:

FNAs were done on 150 patients with clinical suspicion of tuberculosis presenting with lymphadenopathy. Smears from the aspirates were processed for routine cytology and the conventional ZN method. The remaining material in the needle hub and/or the syringe was used for the bleach method. The significance of the bleach method over the conventional ZN method and cytology was analyzed.

Results:

Among the 150 aspirates, 57% (85/150) were indicative of tuberculosis on cytology, 37% (55/150) were positive for AFB on conventional ZN method, and the smear positivity for AFB increased to 41% (62/150) on bleach method.

Conclusion:

The bleach method is simple, safe and inexpensive. It improves the microscopic detection of AFB and can be a useful contribution to routine cytology.

Comparative study of Smear Microscopy, Rapid Slide Culture, and Lowenstein - Jensen culture in cases of pulmonary tuberculosis in a tertiary care hospital

BACKGROUND

Tuberculosis (TB), a dreadful disease known to mankind continues to be a problem in a developing country like India. The incidence of people getting infected with TB is on the rise due to compounding factors like coinfection with the human immunodefiency virus and multidrug-resistant strains. There is a definitive need for early diagnosis and treatment of TB to curb transmission of the infection. Direct smear microscopy, though cheap and rapid, lacks sensitivity. Isolation of Mycobacterium tuberculosis in culture requires a long time, because of which there is a need for a rapid method which has good sensitivity and specificity for the detection of M. tuberculosis. The present study was undertaken to determine the test which diagnoses TB rapidly and to compare the sensitivity of smear microscopy, concentration method, rapid slide culture, and Lowenstein - Jensen (LJ) culture.

MATERIALS AND METHODS

Sputum samples of 200 patients were subjected to direct smear and concentration by modified Petroff's method. The concentrated sputum was also taken for slide culture using human blood medium and inoculated on LJ media.

RESULTS

LJ culture was positive in 47 (23.5%) cases, of which three were nontubercular mycobacteria. Using LJ culture as the standard method, the sensitivity of direct smear, concentration method, and rapid slide culture method was 68, 83, and 89%, respectively, and specificity was 100% in all the three tests.

CONCLUSION

Rapid slide culture showed good sensitivity which was comparable to and next in efficacy to LJ culture and this technique can be adopted in the Revised National Tuberculosis Control Program (RNTCP) as it is a rapid, cheap, sensitive, and specific method.

Diagnostic role of the antibody response to the 38kDa, 16kDa proteins and lipoarabinomannan of mycobacterium tuberculosis

The antibody response to the 38kDa, 16kDa and Lipoarabinomannan (LAM) antigens ofMycobacterium tuberculosis was evaluated using three different ELISAs based on these antigens. The study group included tuberculosis patients (n=52), patients with HIV and TB co-infection (n=10), other chest symptomatics (n=5), HIV infected individuals (n=10), leprosy cases (n=7) and healthy controls (n=75). The results indicate that the 38kDa and LAM based ELISA for IgM/IgG has a low specificity (ranging from 69-85%) and sensitivity (ranging from 55-78%). When three ELISAs are carried out on a single patient the probability of detection of tuberculosis was significantly increased to 95.2% indicating that a single ELISA test is of low sensitivity and that a combination of ELISA's may be needed to be of any value as a diagnostic test for tuberculosis. Additionally, a western blot assay of the serum antibody response to protein fraction ofM. tuberculosis was analysed in 15 tuberculosis patients and five healthy controls. A multiple antibody response to various M.tuberculosis proteins was observed which varied from patient to patient as compared to controls who showed a single 38-39 kDa protein band positivity. These finding suggest that a western blot assay which determines the antibody response to a set of antigenic components ofM. tuberculosis could be a better serological test for the diagnosis of tuberculosis in our population.

An appraisal of PCR-based technology in the detection of Mycobacterium tuberculosis

Tuberculosis is an under-recognized yet catastrophic health problem, particularly in developing countries. The HIV pandemic has served to increase the number of susceptible individuals, and multidrug-resistance and poor socioeconomic conditions also augment the prevalence and the consequences of the disease. To control the disease and its spread, it is vital that tuberculosis diagnostics are accurate and rapid. Whereas microscopy and culture have several limitations (low sensitivity is a problem for the former, while the latter has a delayed turnaround time), PCR-based techniques targeting regions of the Mycobacterium tuberculosis genome such as IS6110 have proved to be useful. The purpose of this review is to assess the use of PCR-RFLP, nested PCR and real-time PCR protocols and the choice of target regions for the detection of M. tuberculosis. Real-time PCR for the detection of M. tuberculosis target genes in clinical specimens has contributed to improving diagnosis and epidemiologic surveillance in the past decade. However, targeting one genome sequence such as IS6110 may not by itself be sufficiently sensitive to reach 100% diagnosis, especially in the case of pulmonary tuberculosis. Additional testing for target genome sequences such as hsp65 seems encouraging. An interesting approach would be a multiplex real-time PCR targeting both IS6110 and hsp65 to achieve comprehensive and specific molecular diagnosis. This technology needs development and adequate field testing before it becomes the acceptable gold standard for diagnosis.

Tuberculosis of spine

Tuberculosis of the spine is one of the most common spine pathology in India. Over last 4 decades a lot has changed in the diagnosis, medical treatment and surgical procedures to treat this disorder. Further developments in diagnosis using molecular genetic techniques, more effective antibiotics and more aggressive surgical protocols have become essential with emergence of multidrug resistant TB. Surgical procedures such as single stage anterior and posterior stabilization, extrapleral dorsal spine anterior stabilization and endoscopic thoracoscopic surgeries have reduced the mortality and morbidity of the surgical procedures. is rapidly progressing. It is a challenge to treat MDR-TB Spine with late onset paraplegia and progressive deformity. Physicians must treat tuberculosis of spine on the basis of Culture and sensitivity.

Effect of therapy on serum zinc and copper in primary complex of children

Tuberculosis is a global problem especially in children, more so because of the difficulty in the diagnosis of the disease. There are about 0.5 million deaths every year by this disease, worldwide. There are some reports that, during the disease, there are changes in serum concentrations of zinc and copper, which reach towards normal levels during treatment. Such data for children are scarce, especially in reference to India. Our study indicates that there is an insignificant to significant rise in serum zinc levels in various age groups of children after antitubercular therapy (mean 61.89 +/- 3.21 to 65.24 +/- 3.60 microg/dl) and significant fall in serum copper levels in different age groups of children (mean 129.96 +/- 3.18 to 124.91 +/- 3.48 microg/dl). The Cu/Zn ratio also changed significantly from 2.11 +/- 0.12 to 1.92 +/- 0.12. Because evaluation of available diagnostic criteria for primary complex in children has been found to have high sensitivity, and although this criterion is presently not recommended for diagnosis of primary complex of children, further research can prove its utility in diagnosis and treatment of this disease.

Evaluation of anti-A60 antigen IgG enzyme-linked immunosorbent assay for serodiagnosis of pulmonary tuberculosis

BACKGROUND

Problems in the diagnosis of tuberculosis using smear and culture techniques have necessitated the exploration of the utility of serodiagnosis to support clinical suspicion of tuberculosis. Anti-A60 antigen IgG enzyme-linked immunosorbent assay (ELISA) was evaluated as a tool for the diagnosis of active pulmonary tuberculosis.

MATERIALS AND METHODS

ELISA was used for the detection of immunoglobulin G (IgG) against A60 antigen in parallel with other familiar diagnostic methods in 70 patients with pulmonary tuberculosis (Group_I) along with 70 controls showing evidence of latent tuberculosis infection (Group II).

RESULTS

ELISA results were positive in 63 (90%) patients in Group_I compared to three (4%) controls in Group_II. Group_I patients had significantly higher titers of IgG (mean = 750.79 +/- 115.87 U/ml against the A60 antigen as compared to Group II controls (mean = 206.67 +/- 20.81 U/ml (P < 0.0001). The overall sensitivity and specificity obtained using ELISA were 90 and 95.7% respectively in active pulmonary tuberculosis. Ziehl-Nielsen (Z-N) stains for acid-fast bacilli were positive in 60 (85.7%) patients. In 48 (68.6%) patients, M. tuberculosis grew on both Lowenstein-Jensen (L-J) medium and BACTEC MGIT 960 liquid medium with mean detection times of 45 and 8 days respectively. Tuberculin skin test was positive in 38 (54.3%) patients. Chest X-ray results were consistent with the diagnosis of pulmonary tuberculosis in 53 (75.7%) patients.

CONCLUSION

Anti-A60 IgG ELISA results were significantly positive and associated with elevated antibody titers in pulmonary tuberculosis as compared to latent mycobacterium infection. The high diagnostic performance of the test makes it a useful, simple and rapid supporting tool to validate clinical suspicion of active pulmonary disease.