Early and rapid microscopy-based diagnosis of true treatment failure and MDR-TB

SETTING: Damien Foundation tuberculosis (TB) control project in Bangladesh. OBJECTIVE: Early diagnosis of true TB treatment failure and multidrug resistance (MDR) for more efficient DOTS-Plus. DESIGN: Prospective comparison of performance on smear-positive sputum of fluorescein diacetate (FDA) vital staining vs. culture, and of slide drug susceptibility testing (slide DST) vs. the Lowenstein-Jensen (LJ) proportion method. RESULTS: FDA reached 92% positive and 97% negative predictive value directly on fresh sputum, but only 94% and 62%, respectively, on transported smears. Accuracy on washed cetylpyridinium chloride transported sputum was similar to that on fresh sputum. Slide DST on fresh smear-positive sputum failed less often than LJ DST, with 96% accurate results for rifampicin and MDR-TB diagnosis. Good results were obtained for isoniazid (90% accuracy), but not for ethambutol or streptomycin. CONCLUSIONS: We can confirm that FDA staining allows rapid screening for viable acid-fast bacilli and true treatment failure in delayed smear converters or smear-defined failures, while slide DST assures fast and accurate confirmation of MDR-TB in selected populations. The tests can be applied safely in resource-poor settings. Their successive use could be an efficient strategy for screening and an early start on standardised regimens of DOTS-Plus candidates.