Isolation prevalence of pulmonary non-tuberculous mycobacteria in Ontario, 1997-2003

Background: The prevalence of pulmonary non-tuberculous mycobacteria (NTM) infection is reportedly increasing. A study was undertaken of the "isolation prevalence'' of pulmonary NTM in Ontario, Canada between 1997 and 2003 and the frequency of pulmonary NTM "disease''. Methods: In a retrospective cohort, the "isolation prevalence'' was studied by reviewing all positive NTM culture results from the Tuberculosis and Mycobacteriology Laboratory, Ministry of Health and Long-Term Care in Toronto from 1997 to 2003. This laboratory identifies at least 90% of NTM isolates in Ontario, Canada. Prevalence was compared between years using a negative binomial model. To study the frequency of "disease'' (defined by American Thoracic Society criteria), the records of patients who had an isolate in 2003 and had been assessed at our hospital were reviewed. Results: 22 247 pulmonary isolates were obtained from 10 231 patients. The "isolation prevalence'' of all species (excluding Mycobacterium gordonae) was 9.1/100 000 in 1997, rising to 14.1/100 000 by 2003 (p<0.0001) with a mean annual increase of 8.4%. Similar increases were observed for individual species. 200 patients assessed at our institution were studied using American Thoracic Society criteria for "disease''. Microbiological criteria were fulfilled by 37%. Of patients with adequate data, 74% fulfilled clinical criteria, 77% fulfilled radiological criteria and 33% fulfilled all criteria. Conclusions: The "isolation prevalence'' of pulmonary NTM has significantly and rapidly increased in Ontario; a sizeable proportion of patients are likely to have "disease''.