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

Abstract

Rationale: The prevalence of pulmonary non-tuberculous mycobacterial (NTM) infection is reportedly increasing. Objectives: To study 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, we studied “isolation prevalence” 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 with a negative binomial model. To study the frequency of “disease” (defined by American Thoracic Society criteria), we reviewed records of patients who had an isolate in 2003 and had been assessed at our hospital. Measurements and Main Results: There were 22,247 pulmonary isolates from 10,231 patients. The “isolation prevalence” of all species (excluding Mycobacterium gordonae) was 9.1/100,000 in 1997 and rose to 14.1/100,000 by 2003 (p<0.0001), with an average annual increase of 8.4%. Similar increases were observed for individual species. Two hundred patients assessed at our institution were studied using American Thoracic Society criteria for “disease.” Microbiologic criteria were fulfilled by 37%. Of patients with adequate data, 74% fulfilled clinical criteria, 77% fulfilled radiologic 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 likely have “disease.”