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

<sec><title>BACKGROUND</title>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.</sec><sec><title>OBJECTIVE</title>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.</sec><sec><title>RESULTS</title>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.</sec><sec><title>CONCLUSION</title>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.</sec>