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.