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Non-tuberculous mycobacteria among previously treated tuberculosis patients with microscopy-positive and Xpert-negative results in Niger

M B Souleymane(1,5) A Yacouba(2,3) T Decroo(4) N Lorent(6) L Rigouts(5,7)

1:Damien Foundation, Niamey, Niger; 2:Université Abdou Moumouni de Niamey, Faculté des Science de la Santé, Niamey, Niger; 3:Laboratoire National de référence TB, VIH et Resistance aux anti-microbiennes, Niamey, Niger; 4:Institute of Tropical Medicine, TB-HIV Unit, Antwerp, Belgium; 5:University of Antwerp, Department of Biomedical Sciences, Antwerp, Belgium; 6:University Hospitals Leuven, Leuven, Belgium; 7:Institute of Tropical Medicine, Unit of Mycobacteriology, Antwerp, Belgium

Disease caused by non-tuberculous mycobacteria (NTMs) shares many clinical features with tuberculosis (TB), challenging differential diagnosis. GeneXpert currently used for TB screening only detects Mycobacterium tuberculosis complex. This study explored the causes of microscopy-positive but Xpert-negative results in patients with chronic lung disease. 

Descriptive cross-sectional study was conducted between July 2022 and June 2023 in four tuberculosis facilities in Niger. It included any patient previously treated for TB presenting with a microscopy-positive but Xpert-negative result, for whom sputum samples were cultured on solid medium. All sputum samples collected had undergone culture and direct rrs PCR sequencing. Positive cultures also had rrs PCR and Sanger sequencing. 

We included 59 patients, predominantly male (sex ratio=5.5), aged 49.3 (±14.8) years, with mean BMI 17.4 (±3.15) kg/m2. Respiratory symptoms were found in 94.9% of patients, and majority (93%) had abnormal chest X-rays. Half (45.8%) of samples grew mycobacteria, while 84.7% were positive by direct PCR: 13 were only positive by direct PCR, three only by culture, and seven by both. Twenty-two different NTM species were identified, majority belonging to the M. intracellulare complex, followed by M. palustre. One patient was positive for M. tuberculosis complex by PCR and culture. On multivariate logistic analysis, no risk factor was associated with detection of NTMs. Programmatic monitoring is needed to assess their clinical relevance.

NTMs are increasingly isolated from previously treated TB patients in Niger. It is important to isolate, identify and assess the clinical relevance of these mycobacteria, as treatment strategies for TB and respiratory NTM infections differ.

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