Sputum microscopy is the main casefinding tool in tuberculosis control programmes. The technique of smear preparation is an important step which needs to be simple for wide applicability. It is often stressed that smear should be prepared from the purulent portions of the sputum as they are likely to have more number of bacilli. It may not be possible for the microscopist/paramedical worker at the periphery to strictly follow this procedure. Hence, a study was conducted to compare the sensitivity of 4 methods of sputum smear preparation viz., direct smear prepared (i) blindly without making any selection of portions of sputum specimen, (ii) from portions of sputum material likely to contain the bacilli, (iii) after mixing up the sputum specimens thoroughly, and (iv) from centrifuged deposit after homogenization of sputum with sodium hydroxide and concentration by centrifugation. Culture was also done for Mycobacterium tuberculosis.

A total of 549 specimens were employed. Positivity rates by four methods were: 79.6% by method (i), 80.3% by method (ii), 80.7% by method (iii) and 77.2% by method (iv). There was no statistically significant difference in the number of positives obtained from different methods. Centrifuged deposit smears proved to be in no way better than the direct smears. The differences in the methods lay only in the classification of positive smear as of a low or high grade.

Culture examination of sputum is known to be the best tool for assessing the prognosis of pulmonary tuberculosis patients. Controlled clinical trials with Short Course Chemotherapy (SCC) have shown that culture examination of sputum at the end of two months elicited a high degree of conversion, while smear results were inferior due to presence of dead organisms in the sputum. But, it is not possible to provide sputum culture facilities in the District TB Programme (DTP). Since smear examination facilities is widely available under the DTP, this paper examines the comparability of smear results with culture in patients treated with SCC. It also examines the value if any, of an early evaluation of the treatment outcome with SCC under operational conditions by doing smear examination at two months. Data from two operational studies on SCC are utilised for this purpose.

Of 256 total patients examined, 62 were smear positive at the end of two months, but 41 of them were excreting non- viable bacilli and were culture negative. Nevertheless, in predicting the final outcome of chemotherapy, no significant difference was observed between smear and culture examination at the end of two months. Smear positivity at the end of 2 months, by itself, cannot be considered to bode an unfavourable response, whereas negativity had a good probability of a favourable response. Microscopy in SCC gave as reliable a result as culture both during and at the end of chemotherapy. Hence, a properly conducted smear examination is as good as culture for diagnostic and prognostic purposes under operational conditions.