How soon should patients with smear-positive tuberculosis be released from inpatient isolation?

In patients with smear-positive pulmonary tuberculosis who are hospitalized or reside in congregate settings, guidelines recommend airborne infection isolation until sputum smear results are negative. Studies have identified factors associated with delayed sputum smear and culture conversion in patients with tuberculosis. Because these studies did not use methods of survival analysis, estimates of time to sputum smear conversion that are based on initial patient characteristics are not available. The ability to predict time to sputum smear conversion could be useful for programmatic planning and patient counseling.

We performed a cohort study using survival analysis to identify factors associated with time to sputum smear and culture conversion. We defined the time to sputum smear conversion as the time elapsed from the start of treatment to the first date of sustained conversion.

Ninety-eight patients had sputum smear samples positive for acid-fast bacilli. Lower initial smear grade (on 1+ to 4+ scale) and absence of cavitation on chest radiograph were associated with earlier sputum smear conversion in bivariate analysis. In multiple regression analysis, initial smear grade (hazard ratio, 0.45; 95% confidence interval, 0.35-0.57) and drug resistance (hazard ratio, 2.30; 95% confidence interval, 1.08-4.89) remained statistically significant; a model comprising only initial smear grade performed almost as well. Predictors of sputum culture conversion were similar.

Initial smear grade was the strongest predictor of time to sputum smear and culture conversion in patients with pulmonary tuberculosis and may be a useful predictor for programmatic planning and patient counseling.