Longitudinal epidemiology of pulmonary nontuberculous mycobacteria and tuberculosis in Singapore (2006-2024): Emerging dominance of Mycobacterium abscessus

BACKGROUND: Nontuberculous mycobacteria (NTM) are increasingly recognized as important pulmonary pathogens, with rising incidence reported globally as tuberculosis (TB) declines. While epidemiology is well described in temperate regions, long-term data from tropical, high-density cities such as Singapore remain scarce. Prior local studies suggested a shift from Mycobacterium avium complex (MAC) to M. abscessus as the predominant NTM species, but comprehensive longitudinal analyses are lacking. METHODS: We performed a retrospective review of all respiratory mycobacterial cultures at Singapore General Hospital between 2006 and 2024. Pulmonary NTM (pNTM) was defined using 2007 ATS/IDSA microbiologic criteria (≥2 specimens with same species or one positive BAL/biopsy), and pulmonary TB (pTB) as a single culture-positive respiratory specimen. Only the first isolate per patient per species was included. ICD-10 coding data (2018-2024) were also analysed to verify trends. RESULTS: A total of 3877 pTB and 1825 pNTM cases met inclusion criteria. Incidence of pNTM increased from 35 to 65 per 100,000 patient-years, while pTB declined from 225 to 70 per 100,000 patient-years. ICD-10 coding data confirmed similar trends, with pTB incidence declining from 185 to 41 per 100,000 patient-years between 2018 and 2024, while pNTM remained stable at 40-43. Species distribution, derived from microbiological isolates, showed a steady decline in MAC and a marked rise in M. abscessus, which surpassed MAC as the most common species after 2014. CONCLUSION: pNTM incidence has risen substantially in Singapore, now approaching that of TB. The emergence of M. abscessus as the predominant NTM species has important clinical and public health implications, underscoring the need for ongoing integrated surveillance and tailored management strategies in tropical urban environments.