Characteristics associated with reported sputum culture conversion in the era of re-emergent Mycobacterium tuberculosis in the State of North Carolina, 1993-1998.

OBJECTIVE: To determine predictors of sputum culture conversion among patients undergoing treatment for pulmonary tuberculosis.
DESIGN: Cohort study based on data collected through the expanded tuberculosis control program in the State of North Carolina, USA. Survival analysis using Kaplan-Meier product-limit estimator and Cox proportional hazards models was employed to compute estimates for time to sputum conversion and rate ratios, respectively.
RESULTS: Sputum conversion was reported in 1144 of 1735 cases (66%). Documented conversion rose significantly from 52.9% at baseline to a peak of 95.1% by the end of the study, representing a 5.1% annual increase in the proportion of patients with reported conversion (P = 0.007). Patients co-infected with the human immunodeficiency virus (HIV) had a 46% lower rate of sputum conversion than non-HIV-infected TB patients (adjusted hazard ratio [HR] 0.54, 95%CI 0.44-0.67). Other significant predictors of reported conversion rates included directly observed therapy (DOT) (P = 0.02), the number of drugs used in the therapy regimen (P = 0.001), and non-injectable drug use (P = 0.012).
CONCLUSION: The rate of reported sputum culture conversion in TB patients was low, consistent with an earlier population-based report. The symbiotic relationship between HIV and mycobacterial infection might be a factor that compromised response to therapy in coinfected individuals.