[In 76% of patients with active tuberculosis treated with triple therapy (isoniazid-rifampicin-pyrazinamide) cultural conversion precedes microscopic conversion].

The time course of smear and culture conversion was studied in 50 previously untreated patients with cavitary pulmonary tuberculosis. Treatment consisted of isoniazid, rifampicin and pyrazinamide for three months, followed by isoniazid and rifampicin. After eight weeks of treatment, negative smears and cultures were obtained in 46 and 84% of the patients, respectively. In 76% of patients, cultural conversion preceded smear conversion, and in 24% of the patients, cultural conversion occurred up to 6 weeks after smear conversion. Thus, the time course of smear conversion provides reliable information on the loss of infectivity in patients with pulmonary tuberculosis receiving chemotherapy.