Risk Score to Predict Time-to Sputum Smear and Culture Conversions in Patients Treated with Shorter MDR Tuberculosis Regime in Guinea: A Retrospective Cohort Study

Abstract

Background Sputum smear and culture examination were used as bacteriological marker to monitor multidrug-resistant tuberculosis (MDR-TB) treatment. We aimed to identify the strongest contributing factors that affect time-to sputum bacteriological conversion, and to develop a practical risk scoreMethods Patients treated with shorter MDR-TB treatment regime between June 07, 2016 and June 22, 2018 from three major drug-resistance TB centres in Guinea, who had a positive smear or culture at baseline, and who had rifampicin resistance were analysed. Sputum bacteriological conversion was defined as two consecutive negative smear or culture taken at least 30 days apart. Cox regression model was used to analyse time-to initial sputum conversion, and to identify influencing factors. A simple risk score was constructed using the regression coefficients from each final model. Time-dependent AUC was used to determine the optimal time points of bacteriological conversion.Results 75% (173/232) of patients with a positive smear and culture at baseline were analyzed. A total, 90.2% (156/173) and 89% (154/173) of the patients had smear and culture conversions in a median of 59 days (inter-quartile range: 59 – 61) respectively. Lower colony count (< 3 +) of initial culture (aHR = 1.52, 1.09 – 2.14) and previously history of TB treatment (aHR = 2.10, 1.26 – 3.51) were more likely to have culture conversion, while only the higher BMI (aHR = 1.10, 1.03 – 1.18) was associated with rapid smear conversion. The predicted risk score from independent predictors showed good discrimination (0.855 ± 0.023 and 0.883 ± 0.02 respectively for smear and culture conversions). Time-to initial culture conversion provided a better discriminative capacity (AUC) to detect patients with higher chance to being treatment success during the first three months.Conclusion The identified predictors can be considered to improve the management of MDR-TB patients. The optimal time points for culture conversion was three months in shorter regime. Keywords: Conversion, Multidrug-resistant, Tuberculosis, Guinea.