SPUTUM SMEAR CONVERSION DURING DIRECTLY OBSERVED TREATMENT FOR TUBERCULOSIS

Setting: Treatment program for tuberculosis in a refugee camp in Thail and. Objectives: To determine the cumulative frequency of conversion o f sputum smears examined by direct microscopy by month of treatment an d to identify factors predicting failure to convert. Methods: Analysis of conversion based on three sputum smear examinations (performed mon thly) in a cohort of patients with sputum smear-positive tuberculosis treated with a directly observed daily regimen containing rifampicin t hroughout. Nested case-control study of patients failing to convert de finitively within four months compared to controls who did convert. Re sults: Sputum conversion after the 2-month intensive phase was 75.0%, with a range from 61.7% to 90.9% in patients with initially strongly- and weakly-positive smears, respectively. The strongest predictor iden tified for no definitive conversion within four months of treatment wa s a positive sputum smear result at the end of the 2-month intensive p hase (adjusted relative odds 4.2, 95% confidence interval 1.5-11.4). O f those patients who did not convert, positive smears were an isolated phenomenon in 15, repeatedly in four who definitely converted with a prolongation of treatment, and persistently positive in two requiring a re-treatment regimen. Conclusions: Definitive sputum smear conversio n is judged to be slower if a strict program of sputum smear examinati on is undertaken than under routine program conditions, but positive r esults late in the course are commonly an isolated phenomenon and poss ibly of little significance. Sputum smear results at two months strong ly predict bacteriologic results beyond three months of treatment, and thus identify cases who might benefit from a prolongation of the inte nsive phase.