Changing incidence and characteristics of non-tuberculous mycobacterial infections in Scotland and comparison with Mycobacterium tuberculosis complex incidence (2011 to 2019)


 
 
 An increase in infections with non-tuberculous mycobacteria (NTM) has been noted globally and their incidence has overtaken that of Mycobacterium tuberculosis complex (MTBc) in many countries. Using data from a national reference laboratory, we aimed to determine if this trend was observed in Scotland.
 
 
 
 We undertook a retrospective review of all NTM isolates received by the Scottish Mycobacteria Reference Laboratory (SMRL) over 9 years from 2011 to 2019 inclusive. Clinical episodes were defined as per 2017 BTS and 2020 ATS/ERS/ESCMID/IDSA NTM guidelines. These rates were compared with Scottish tuberculosis rates over the same period.
 
 
 
 Of 8552 NTM isolates from 4586 patients in 2011 to 2019, 7739 (90.5%) were considered clinically relevant. These represented 2409 episodes of NTM infection, with M. avium, M. intracellulare and M. abscessus complex being most common. 1953 (81.1%) were pulmonary NTM infection episodes from 1470 patients and 456 extra-pulmonary episodes from 370 patients. We estimated a rise in incidence from 3.4 to 6.5 per 100,000 person-years (2011-2019 inclusive) with an increase in NTM incidence over MTBc incidence in Scotland by 2017.
 
 
 
 The incidence of NTM infection in Scotland has overtaken MTBc incidence. NTM infection leads to a costly healthcare burden, possibly as much as UK £1.47 million (US$ and Euro 1.73 million) annually. We recommend standardisation of isolate referral with clinical surveillance and implementation of agreed standards of care delivered through multi-disciplinary teams. This would improve diagnosis and patient management as well as assessment of diagnostics and novel treatments through clinical trials.
