Prevalence of non-tuberculous mycobacteria among people presumed to have tuberculosis, positive for acid-fast bacilli in Mali
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Background
Non-tuberculosis mycobacteria (NTMs) are environmental agents that can cause opportunistic pulmonary disease in humans and animals which is often misdiagnosed as tuberculosis (TB). In this study, we describe the cases of NTMs identified during the first national anti-TB drug-resistance survey conducted in Mali, and associated risk factors.
Methods
Sputum was collected from people presenting for pulmonary TB diagnosis, from April to December 2019, regardless of age. Microscopy-positive patients were enrolled and were tested by GeneXpert MTB/RIF. Cases that tested negative for the Mycobacterium tuberculosis complex (MTBc) were tested for presence of mycobacteria by amplification of the IS 6110 and 16SrRNA genes through double quantitative real-time PCR, followed by nested PCR and Sanger sequencing of the IS 6110 -negative samples for NTM species identification.
Results
A total of 1,418 sputum smear-positive patients were enrolled, including 1,199 new cases, 211 previously treated cases and 8 whose previous treatment history was unknown. Based on the results of GeneXpert MTB/RIF and in-house PCR methods, 1331 (93.9%) patients were positive for MTBc, 48 (3.4%) for NTMs and for 39 (2.7%) no species identification was possible. Advanced age (65 and over) (OR 8.8, p=0.001) and previous TB treatment (OR 3.4 and p=0.016) were the risk factors statistically associated with NTM detection. M. avium complex (MAC) was the predominant NTM species, detected in 20 cases.
Conclusion
Detection of NTMs in people presumed to have TB is an ongoing challenge, confounding correct TB diagnosis. Concomitant use of microscopy and GeneXpert testing among at-risk individuals could lessen confusion.
