Relationship between sputum smear grading and smear conversion rate and treatment outcome in the patients of pulmonary tuberculosis undergoing dots--a prospective cohort study.

BACKGROUND: The Smear Conversion Rate (SCR) is an operational indicator for the Directly Observed Treatment Short-course (DOTS) strategy of Revised National Tuberculosis Control Programme (RNTCP) in India. The present study was undertaken to determine the relationship between sputum smear grading and smear conversion rate among the Category I smear positive pulmonary tuberculosis patients undergoing DOTS.

METHODS: A prospective cohort study was conducted among the Category I smear positive pulmonary tuberculosis patients registered under DOTS at GTB, Karawal Nagar and Shahdara Chest Clinics of Delhi. Sample size for the present study was calculated on the basis of a similar study of a retrospective design conducted at LRS Institute of Tuberculosis and Respiratory diseases New Delhi, India using statistical software Epi Info version 6. Accordingly, a total of 338 sputum smear positive patients with 169 each in the High Positive Cohort (pre-treatment sputum grading 3+) and Low Positive Cohort (pre-treatment sputum grading 2+, 1+ and Scanty) were followed periodically at two months (end of Intensive Phase), at three months (after one month extension of Intensive Phase), at two months of Continuation Phase and then at the end of the treatment to record the sputum AFB result and treatment outcome as per the RNTCP guidelines. Data was analyzed using SPSS Version -15.

RESULTS: After two months (end of the intensive phase), SCR was 57.9% (98 of 169) among the High Positive and 71.6% (121 of 169) in the Low positive cohort ( p -0.008). After three months (one month's extension of intensive phase), cumulative SCR was 85.2%( 144 of 169)) in the High Positive and 92.3% (156 of 169) in the Low Positive cohort (p-0.03). Cure rate was 82.8% (140 of 169) in the High Positive and 84.6% (143 of 169) in the Low Positive cohort. Default rate was 3% (five of 169) in the High Positive and 5.3% (nine of 169) in the Low Positive cohort. Failure rate was 11.2% (19 of 169) in the High positive and 6.5% in the Low positive Cohort (11 of 169). Only one patient (0.6%) in each High and Low Positive cohort died during course of treatment (p -0.631). Treatment outcome was further compared among the patients according to their sputum status achieved at two and three months of the treatment after ignoring their initial sputum status. The cure rates for the patients who converted at two months was 90.9% (199 of 219) and for those who did not convert at two months, was 74.3% (84 Of 113) (p -0.000). Similarly, the cure rate for the patients who converted at three months was 84% (68 of 81) and for those who did not convert at three months was 55.2% (16 of 29) (p-0.01).

INTERPRETATION: Patients with higher grades of sputum positivity at the beginning of the treatment have significantly lower SCR at the end of intensive phase and even after extending the intensive phase for one month. Hence, they are likely to remain infectious for a longer duration and continue to transmit infection in the community. Therefore, these patients demand to have more stringent self-precautionary measures to break the chain of infection in the community. The SCR at two months and three months as an operational indicator should be given more importance rather than being practised only as a documentation and academic exercise. The patient should be investigated for the possible co-morbid conditions and drug resistance which could be a cause for the persistent sputum smear positivity at two and three months and hence poor treatment outcome.