Mycobacterium avium complex, an emerging pathogen in Massachusetts.

We report a study of 1,953 patients whose laboratory records from 1972 through 1983 at the Massachusetts Mycobacteria Reference Laboratory indicated the isolation of Mycobacterium avium complex (MAC) organisms. At least one clinical specimen from each patient during this period exhibited the organism. The incidence of isolation of MAC has increased fivefold since 1972, with a doubling of the number of patients with positive MAC specimens from normally sterile sites occurring since 1980. A concomitant increase of more than fourfold in other nontuberculous mycobacteria has occurred. Most isolates came from high-density population centers. Communities whose drinking water comes from a distant rather than a local source were more likely to have patients with MAC.