Evaluation of bacteriological diagnosis of smear positive pulmonary tuberculosis under programme conditions in three districts in the context of dots implementation in India.

Objective: To study the smear and culture positivity rates in pulmonary tuberculosis patients declared as smear positive in the districts of North Arcot (Tamil Nadu), Raichur (Karnataka) and Wardha (Maharashtra) in India in order to evaluate the diagnosis of pulmonary tuberculosis at the field level under programme conditions. Methods: Two specimens of sputum from each of 320 patients in North Arcot, 314 patients in Raichur and 302 patients from Wardha district, all of whom had been reported as smear-positive at the field level, were examined by smear and culture. Findings: The proportion of specimens found to be smear-negative was 4.7% in North Arcot and 5.7% in Raichur as against 38.7% in Wardha. The proportions of culture negative specimens were 5.7% and 6.3% respectively in North Arcot and Raichur, while it was 35.6% at Wardha. The difference in the smear and culture negativity between Wardha and the other two districts was highly significant. Conclusions: The study revealed an unacceptably high level of false positives in sputum smear microscopy in the Wardha district. This could be attributed to the absence of systematic and intensive training in smear examination consequent to the non-implementation of the DOTS strategy in this district and a high standard of training offered in the RNTCP implemented districts.

Comparison of different methods of assessing in vitro resistance of Mycobacterium tuberculosis to rifampicin.

BACKGROUND & OBJECTIVES: Definitions of in vitro resistance to rifampicin in strains of Mycobacterium tuberculosis by different methods have not been consistent, leading to variations in the interpretation and validity of results. This study compared three methods of defining in vitro resistance to rifampicin. METHODS: (i) A total of 598 clinical isolates of M. tuberculosis were concurrently compared by the minimal inhibitory concentration (MIC) and the proportion method on Lowenstein-Jensen medium; (ii) 54 strains tested by the MIC method were retested by the proportion method and the BACTEC radiometric method; and (iii) 72 strains which yielded an MIC of 64 mg/l by the MIC method were retested by the same method. RESULTS: Out of 598 cultures tested by the MIC and the proportion methods, identical classification as susceptible or resistant was observed in 99.7 per cent. A 100 per cent agreement was observed when 54 strains were tested by the MIC, proportion and BACTEC radiometric methods. When 72 strains with an MIC of 64 mg/l were retested by the same method, 61 (85%) yielded a lower MIC, 9 (12%) gave the same MIC while 2 (3%) yielded a higher MIC of 128 mg/l, reflecting perhaps the inherent limitations of the variations in the inoculum size. INTERPRETATION & CONCLUSION: All 3 definitions of resistance, viz., an MIC of 128 mg/l, a proportion of 1 per cent or more on 40 mg/l by the proportion method, both on L-J medium and a growth of 1 per cent or more on 2 mg/l by the radiometric method were found to be equally satisfactory.