Evaluation of microscopically quantitative loads of bacilli as early predictors of TB treatment outcome

BACKGROUND Two-month smear conversion has been adopted instead of cultures to predict unfavourable bacteriological outcomes in TB treatment. However, this approach is limited by lower sensitivity and specificity. OBJECTIVE In absence of early-stage biomarkers of treatment response, we investigated the association between bacteriological outcome and microscopy data with auramine and fluorescein diacetate stains at baseline and during the first 2 weeks of treatment in the context of the OneRIF trial. This is a secondary analysis of data collected during the OneRIF trial. RESULTS Failure or relapse occurred in 15 patients of 321 treated with double-dose R. Only quantitative baseline auramine significantly predicted failure or relapse: for every 100 bacilli per field increase, there was 5% higher odds of having an unfavourable bacteriological outcome. CONCLUSION While quantitative baseline auramine predicted having an unfavourable bacteriological outcome, considering our small data we could not identify any added value in implementing quantitative bacillary load in the first 2 weeks of treatment. These findings should be interpreted with caution as we were limited by the relatively low number of failure and relapse.