Fluorescein diacetate and rapid molecular testing for the early identification of rifampicin resistance in Mali

BACKGROUND: Non-conversion on auramine smear microscopy indicates a lack of treatment response, possibly associated with initial rifampicin-resistant tuberculosis (RR-TB). However, dead bacteria still stain positive and may be detected. Fluorescein diacetate smear microscopy (FDA) shows live mycobacteria only. Therefore, we studied the potential of 2-month (2M) FDA for the identification of initial RR-TB. METHODS: Between 2015 and 2018, we enrolled new smear-positive pulmonary TB patients from five local centres in Bamako, Mali. After baseline screening, sputum samples were collected at 1M, 2M, 5M and 18M. We used rpo B sequencing to identify initial RR-TB. RESULTS: Of 1359 patients enrolled, 1019 (75%) had rpo B sequencing results. Twenty-six (2.6%, 95%CI: 1.7–3.7) had mutations conferring rifampicin resistance. Most frequent rpo B mutations were located at the codons Asp435Val (42.4%) and Ser450Leu (34.7%). Among patients with initial RR-TB, 72.2% were FDA-negative at 2M ( P = 0.2). The positive and negative predictive value of 5M FDA for culture-based failure was respectively 20.0% and 94.7%. CONCLUSION: FDA did not identify the majority of patients with initial RR-TB or culture-based failure. As the full spectrum of mutations identified on sequencing was identified using Xpert, our data support its rapid universal implementation in Mali.