Should we take a history of prior treatment, and check sputum status at 2-3 months when treating patients for tuberculosis?

Setting: Pinetown, South Africa (1975-1983).

Objective: To determine the value of previous treatment history and sputum smear examination at 2-3 months in predicting treatment failure and relapse in tuberculosis patients treated with four drugs given twice weekly for six months under direct observation.

Design: Four cohort studies among 562 ambulant adults with culture positive pulmonary tuberculosis, designed to test the effectiveness of isoniazid 600-900 mg, rifampicin 600 mg, pyrazinamide 2-3 g, and streptomycin 1-2 g, given twice weekly. The same drug regimen was given to all patients irrespective of previous treatment history. Therapy was not changed if smears remained positive at 2-3 months.

Results: Positive predictive values of a history of previous treatment for a positive smear at 2-3 months (18.3%), treatment failure (5.2%), and relapse (9.4%) were poor. Although patients with positive smears at 2-3 months were more likely to fail therapy than patients with negative smears (relative risk=4.5, 95% Confidence Interval [CI]: 1.6-12.8), positive predictive value for treatment failure was only 12.5%. Although relapse was more frequent in patients with positive smears than those with negative smears (9.7% vs 6.2%; P=0.4), most patients who relapsed had been smear negative at 2-3 months (18/21).

Conclusion: A four-drug rifampicin-containing regimen can safely be given twice weekly under direct observation to both new and retreatment cases, and the 2-3 month smear examination can safely be omitted.