Predictors of delayed sputum culture conversion in tuberculosis patients

Introduction: Failure to sputum culture conversion at the second month of tuberculosis (TB) treatment has been reported to be a predictor of patient infectivity and treatment failure. Aim: To identify factors associated with delayed sputum culture conversion among pulmonary TB patients under anti-TB treatment. Methods: Retrospective cohort of 136 adult patients with culture-proven pulmonary TB referred to an urban Chest Disease Centre (January 2006-June 2009). Delayed sputum culture conversion was defined as persistent culture positivity after 2 months of treatment. Socio-demographic, clinical, radiological, microbiological, and therapeutic data were evaluated. Univariate and multivariate logistic regression analyses were performed. Results: Mean age was 43.3 (± 13.8) years; 75.0% were male. Median sputum culture conversion time was 46 days. Delayed sputum culture conversion was found in 27.2% (n=37) of patients. In univariate analysis, unemployment (38.0% vs 20.9%, p=0.031), HIV positivity (53.3% vs 24.0%, p=0.028), bilateral radiological involvement (42.0% vs 19.0%, p=0.005), cavitary disease (32.6% vs 15.9%, p=0.041), and colony counts ≥ 100 (33.7% vs 8.7%, p=0.018) were risk factors for persistent positive culture. In multivariate logistic regression analysis, only bilateral radiological involvement (odds ratio (OR) 3.7, 95% confidence interval (CI): 1.5–9.0) and higher colony counts (OR 5.8, 95% CI: 1.2–27.4) were independently associated with delayed sputum culture conversion. Conclusions: Delayed sputum culture conversion was found in approximately one third of patients. Bilateral radiological involvement and higher colony counts were independent risk factors for delayed sputum culture conversion.