Prevalence of nontuberculous mycobacteria isolates and pulmonary disease from respiratory tract samples in persons investigated for presumed tuberculosis from three West African countries, an analysis of three prospective cohort studies.

backgroundIn West Africa, the isolation of nontuberculous mycobacteria (NTM) is increasingly reported among individuals evaluated for tuberculosis (TB). However, the clinical relevance of NTM detection from respiratory tract samples remains unclear, creating uncertainty for clinicians when NTM are identified. As a first step in addressing this gap, we aimed to estimate the prevalence of NTM isolation from mycobacterial cultures among individuals with presumed TB, regardless of TB treatment history, and determine the proportion who met international diagnostic criteria for NTM pulmonary disease (NTM-PD).

methodsWe analysed data from three prospective cohort studies conducted in Ghana, Nigeria, and Niger using a descriptive analysis. Sputum samples were collected from all individuals presenting with presumed TB for smear microscopy and culture; additionally, Xpert MTB/RIF testing was performed in Ghana and Niger. NTM species were identified using GenoType CM/AS and/or rrs/rpoB sequencing. Drug-susceptibility testing was performed with phenotypic and genotypic methods. Clinical data were extracted from medical records and structured questionnaires, and patients underwent chest radiography.

resultsOut of 9,981 symptomatic individuals screened, 938 were subjected to mycobacterial culture, of whom 99 (Ghana: 31; Nigeria: 42; Niger: 26) had at least one NTM isolate. The prevalence of NTM detection among mycobacterial cultures was 10.6% (95%CI: 8.7%-12.7%). The mean age was 51.6 years, with 61.6% males; 46.5% had a history of TB, and 27.3% were living with HIV. Among the 99 patients, the predominant symptoms were cough (82.8%), weight loss (56.3%), fever (47.5%), and dyspnoea (28.3%). Consolidation was observed on chest x-ray in 73.7% and cavitation in 46.5%. Common NTM species included M. intracellulare (34.3%), M. fortuitum (16.2%), and M. abscessus complex (10.1%). Most M. intracellulare and M. abscessus complex were susceptible to macrolides and aminoglycosides. Of the 49 patients with two or more sputum samples processed for culture at baseline and/or follow up, 15 (30.6%) met the diagnostic criteria for NTM-PD, with all patients exhibiting smear positivity, clinical symptoms, radiological abnormalities and repeated culture of the same NTM species. Mortality for patients who were classified as NTM-PD was 43%.

conclusionThese findings provide insights into the clinical relevance of NTM isolation in TB-endemic settings. Active TB should be excluded in all symptomatic patients, as should other possible explanations such as (post-TB) bronchiectasis with bacterial superinfection, Aspergillus infection) if infrastructure allows, before attributing the clinical presentation to NTM. Until more context-specific epidemiologic and clinical data become available, adherence to NTM-PD diagnostic criteria is recommended to guide appropriate clinical decision-making. CLINICAL TRIAL NUMBER: Not applicable.