Time to sputum smear and culture conversions in multidrug resistant tuberculosis at University of Gondar Hospital, Northwest Ethiopia

Abstract

Background: Sputum smear and culture conversions are an important indicator of treatment efficacy and help to determine treatment duration in multidrug resistant tuberculosis (MDR-TB) patients. There are no published studies of sputum smear and culture conversion of MDR-TB patients in Ethiopia. The objective of this study is to evaluate and compare time to initial sputum smear and culture conversion and to identify factors influencing time to culture conversion.

Methods: A retrospective cohort study was conducted among all culture positive and rifampicin mono resistant (RR) or MDR-TB patients from September 2011 to August 2016 at University of Gondar Hospital. Sputum cultures were collected monthly and conversion was defined as two consecutive negative cultures taken at least 30 days apart. Data were entered using EpiData and exported to SPSS software for analysis. Cox proportional hazard model was used to determine the predictor variables for culture conversion.

Results: Overall, 85.5% (201/235) of the patients converted their cultures in a median of 72 days (inter-quartile range: 44-123). More than half (61.7%) of patients achieved culture conversion within three months. The median time for sputum smear conversion was 54 days (inter-quartile range: 31-72). The median time to culture conversion among HIV positive patients was significantly shorter at 67 days (95% CI, 55.4-78.6) compared to HIV negative patients, 77 days (95% CI, 63.9-90, p = 0.005). Independent predictors of significantly longer time to sputum culture conversion were underweight (aHR = 0.71, 95% CI, 0.52-0.97), HIV negative (aHR = 0.66, 95% CI, 0.47-0.94) and treatment regimen composition (aHR = 0.57, 95% CI, 0.37-0.88). Significantly higher rate of culture conversion was observed in 2015 (aHR = 1.86, 95% CI, 1.1-3.14) and in 2016 (aHR = 3.7, 95% CI, 1.88-7.35) years of treatment compared to 2011.

Conclusions: Majority of patients achieved sputum culture conversion within three months and smear conversion within two months. Patients with identified risk factors were associated with delayed culture conversion. These factors should be considered during management of MDR-TB patients.

Fig 1. Initial sputum culture conversion in 201 of 235 culture-positive patients who had culture conversion.

Fig 2. Kaplan-Meier survival plot of time to initial sputum culture conversion by HIV status.