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

Date Published: June 26, 2018

Publisher: Public Library of Science

Author(s): Agumas Shibabaw, Baye Gelaw, Shu-Hua Wang, Belay Tessema, Pere-Joan Cardona.


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.

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.

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.

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.

Partial Text

Sputum smear and culture conversion from positive to negative is one of the most important interim indicators of the efficacy of anti-tuberculosis treatment regimen. Sputum culture conversion is often used by clinicians to determine the duration of injectable agents and overall duration of multi-drug resistant tuberculosis (MDR-TB) treatment. Predicting the initial time to culture conversion is also important for planning and implementing respiratory isolation [1].

Prolonged periods of infectiousness increase the likelihood of spreading M. tuberculosis including MDR-TB [17]. Based on PMDT guideline of Ethiopia, at least one sputum sample for smear and culture should always be taken at initiation of MDR-TB treatment and repeat sputum specimen should be collected monthly [8]. Serial sputum smear and culture monitoring during MDR-TB therapy allows for assessment of sputum conversion which is important for clinical management and therapeutic planning. To the best of our knowledge, this is the first study in Ethiopia that evaluates time to sputum smear and culture conversion and predictors of initial sputum culture conversion among MDR-TB patients.

Our finding shows that nearly 61% of MDR-TB patients achieve sputum culture conversion by the third month of treatment with median of 72 days. Underweight, HIV negative and the use of Z-E-Km (Am)-Lfx-Eto-Cs treatment regimen composition were associated with significant delayed culture conversion. Patients with lower BMI should be closely monitored during their MDR TB treatment course. Further studies are required to improve understand of the influences of sputum culture conversion on the treatment outcomes in drug-resistant TB patients.




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