Second-line drug resistance markers as indicators of time to sputum culture conversion among selected mycobacterium tuberculosis clinical isolates at the Uganda National Tuberculosis Reference Laboratory

Abstract

Drug-resistant TB continues to be a global public health crisis, with low treatment success rates for Multi Drug Resistant/ Rifampicin Resistant TB and Extensively Drug-Resistant TB. Achieving sustained bacteriological conversion from positive to negative is a renown predictor of TB treatment outcome. However, the overall role of drug resistance on prognosis remains unclear, making it worth investigating in different geographical settings. The study aimed at determining the usefulness of second-line drug resistance markers as indicators of time to sputum culture conversion among selected Mycobacterium tuberculosis isolates at the Uganda National TB Reference Laboratory. A cross-sectional study was conducted on 72 second-line drug resistant clinical tuberculosis isolates referred to the Uganda National Tuberculosis Reference Laboratory between the months of January 2018 and December 2019. The isolates were retrieved, sub-cultured, sequenced and analysed using TBProfiler, an online pipeline. Data were entered into patient datasets where monthly culture conversion time were captured, cleaned and imported into STATA v15 for analysis. This included descriptive, Univariate Cox proportional hazard model analyses with the use of the Kaplan-Meier survival curves. The level of significance was set at 5% and a p-value less or equal to 0.05 was considered statistically significant. Results showed that the median time was achieved at 3 (0 – 12) months across the studied isolates. The rrs Gly1484Thr mutation associated with conferring drug resistance to aminoglycosides was observed to have the shortest median conversion time of 1.5 months, closely trailed by the gyrA Ala90Val with 2.5 months. A single mutation in the gyrA gene locus showed higher converted proportions 70.8% (58.9 – 81.0) than those that had two 8.3% (3.1 – 17.3) or three 2.7% (0.3 – 10.0) mutations. Therefore, the studied second-line drug resistance markers are not responsible for any delays in conversion of sputum from positive to negative in this particular study, although increased levels of drug resistance decreased the proportions of conversion from positive to negative sputum cultures. Continued surveillance and monitoring of the different drug resistance markers are needed to better understand their usefulness as proxy indicators in multidrug-resistant tuberculosis treatment.