Atypical Mycobacterial Infections Might Be on the Rise

Pulmonary infections with “atypical” nontuberculous mycobacteria have been recognized for decades, but reliable estimates of their prevalence are elusive for several reasons: These infections are tricky to diagnose, geographically variable, and untracked by local or federal health departments. Several reports from around the country now suggest that infection rates are rising.

Investigators reviewed all clinical isolates of nontuberculous mycobacteria obtained from Oregon residents during 2005 and 2006. Estimated prevalence of pulmonary infection was 8 to 11 cases per 100,000, with a prevalence in older people (age, ≥50) of about 26 per 100,000 (considerably higher than estimated rates from the 1980s). The incidence of tuberculosis (TB), by contrast, was 7 per 100,000 in that age group during the study period. Among 184 patients with confirmed disease, 59% were women or girls; about half the women and girls had either bronchiectasis or immunosuppressive treatment as a risk factor, whereas only 22% had the classic risk factor of chronic obstructive pulmonary disease.

In a similar but larger study, investigators analyzed isolates of atypical mycobacteria obtained from patients in four large healthcare systems in California, Colorado, Pennsylvania, and Washington State from 2004 through 2006. Estimated disease prevalence ranged from 1 to 6 cases per 100,000, with higher rates in women and older people (age, ≥60); prevalence rose slightly in most age groups during the 3 years of the study. In this study as well, the overall prevalence of infections with atypical mycobacteria considerably exceeded that of pulmonary TB at all study sites.