Time to sputum culture conversion in multidrug-resistant tuberculosis: Predictors and relationship to treatment outcome

Background: Conversion of sputum mycobacterial cultures from positive growth to negative growth of Mycobacterium tuberculosis in patients with pulmonary tuberculosis (TB) is considered the most important interim indicator of the efficacy of anti-TB pharmacologic treatment for multidrug-resistant disease. Objective: To evaluate and compare time to and predictors of initial sputum culture conversion with predictors of treatment outcome for patients with multidrug-resistant TB. Design: Retrospective cohort study. Setting: Latvia. Patients: All civilian patients with multidrug-resistant TB treated with the DOTS-Plus strategy between 1 January and 31 December 2000. Intervention: Individualized treatment for confirmed sputum culture-positive pulmonary multidrug-resistant TB. Measurements: Time to initial sputum culture conversion and treatment outcome. Results: Among 167 patients who were sputum culture-positive at initiation of second-line therapy, 129 (77%) converted in a median time of 60 days (range, 4 to 462 days) and 38 (23%) did not convert. Independent predictors of a longer sputum culture conversion time, using an accelerated failure time regression model, included previous treatment for multidrug-resistant TB, high initial sputum culture colony count, bilateral cavitations on chest radiography, and the number of drugs the initial isolate was resistant to at treatment initiation. Treatment outcomes were statistically significantly worse for patients who did not convert their sputum culture within 2 months. Limitations: Twenty-five percent of patients missed 5 or more monthly sputum collections. Conclusions: Under program conditions in Latvia, most patients with multidrug-resistant TB achieved sputum culture conversion within 12 weeks of starting treatment. Chest radiography and sputum culture drug susceptibility testing can assist physicians in predicting which patients will convert more slowly. Sputum culture conversion is a useful and appropriate interim indicator of treatment outcome in patients with multidrug-resistant TB.