Time to sputum conversion in smear positive pulmonary TB patients on category I DOTS and factors delaying it.

Background: Sputum smear positive pulmonary tuberculosis patients expel infectious viable bacilli for a period following commencement of treatment. Patients on Directly Observed Treatment Shortcourse (DOTS) receive intermittent therapy with multidrug regimen.

Aims: To determine the time to sputum smear and culture conversion following initiation of DOTS treatment and study the factors that influence it.

Methods: A prospective study was undertaken at a tertiary care teaching hospital in Mumbai over a one year period on a cohort of 71 sputum smear positive patients on Category I DOTS treatment. Patients were followed up weekly for upto 20 weeks or until they underwent smear and culture conversion whichever was earlier. At each follow up, specimens were collected and processed for microscopy and culture using standard protocol.

Results: 60/71 [84.55%] patients completed the study. 56/60 [93.3%] patients underwent sputum smear and culture conversion. The median time to smear and culture conversion was end of 5th week [day 35] and 6 1/2 weeks [day 45] respectively. Univariate and stepwise regression analysis showed that patients who had cavitatory disease, high pretreatment smear grade and a past history of tuberculosis were more likely to undergo delayed or nonconversion [P < 0.05].

Conclusion: The time to sputum smear and culture conversion under DOTS is similar to previous antituberculosis regimens. Since viable bacilli continue to be expelled for upto two months, infection control measures should be maintained for such time. Patients with cavitatory disease, high pretreatment smear grade or a past history of tuberculosis need to be monitored more closely.