Nontuberculous mycobacterial disease prevalence and risk factors: a changing epidemiology

Nontuberculous mycobacteria (NTM) are important human pathogens, yet little is known about disease prevalence in the United States. Reports suggest prevalence has increased, particularly in women, but population-based data to substantiate this are lacking. We sought to estimate NTM disease prevalence in Oregon, and describe disease by site, species, and patient demographic characteristics.

We contacted laboratories that performed mycobacterial cultures on Oregon residents in 2005-2006. For each isolate, we obtained source, collection date, species, and patient demographics. We used the microbiologic component of the American Thoracic Society/Infectious Diseases Society of America's pulmonary NTM disease criteria to define cases of pulmonary NTM, and patients with isolates from a normally sterile site were classified as having extrapulmonary disease.

We identified 933 patients with > or =1 NTM isolate. Of these, 527 (56%) met the case definition (annualized prevalence, 7.2 cases per 100,000 persons). Pulmonary cases predominated (5.6 cases per 100,000 persons), followed by skin/soft-tissue cases (0.9 cases per 100,000 persons). Mycobacterium avium complex was the most common species identified in pulmonary cases (4.7 cases per 100,000 persons). Pulmonary disease prevalence was significantly higher in women (6.4 cases per 100,000 persons) than men (4.7 cases per 100,000 persons) and was highest in persons aged >50 years (15.5 cases per 100,000 persons).

NTM are frequently isolated from Oregon residents; more than one-half of all isolates likely represent true disease. Pulmonary NTM is most common among elderly women, and M. avium causes most disease. Future efforts to monitor disease trends should be undertaken, and efforts made to validate the use of the ATS/IDSA microbiologic criteria alone to predict pulmonary NTM disease.