Survey of the negativation of sputum samples in patients with active pulmonary tuberculosis: what is the optimum duration for the isolation?

The risk of contamination by contact with patients with tuberculosis is red uced by isolation of patients until negativation of direct sputum analysis for the research of tuberculosis bacilli. To evaluate the efficacy of this isolation, we compared, in 32 patients with active tuberculosis, the result s of direct examination and culture of the sputum and the clinical outcome. Thirty-two successive patients hospitalized in the same internal medicine unit, received antituberculosis drugs and had 3 sputum examinations per wee k with direct analysis and coiture until negativation of the 3 direct exami nations. Then, isolation ended, At the time of direct-negativation, 14 of t he 32 patients kept positive cultures. In the 18 remaining subjects, the cu ltures became negative, about seven days before direct-negativation. Patien ts with negative cultures had more frequently weight increase (83% versus 7 1%), were more rapidly without fever (11 days versus 19 days), had less cou gh and had less severe radiologic disease (50% versus 75%) compared to pati ents with positive cultures but these differences were not statistically si gnificant due to the small sample size. In tuberculosis patients, 3 succesi ve negative direct sputum examinations do not eliminate the risk of tubercu losis transmission, specially to hospitalized or immunocompromised patients . The risk of contamination in these cases, althought unknown, may be weak. Terminating isolation should not be based on sputum examination alone, but also on other factors such as the clinical course (resolution of cough and fever, weight), the initial number of bacilli, and the severity of the rad iological lesions.