Epidemiology of Infection by Nontuberculous Mycobacteria

Abstract

Using the fluorochrome auramine-O, direct microscopic counts of log phase cells of Mycobacterium avium, M. intracellulare, and M. scrofulaceum (MAIS) group showed excellent correlations with viable spread-plate counts. Accordingly, an enumeration of total acid-fast and MAIS cells by stain and culture (respectively) in groundwaters from three United States regions that differ in their incidence of human infection by MAIS was undertaken. Of 30 state-monitored, undisinfected wells, 11 were in Georgia coastal plain (high incidence), 10 were in the Virginia coastal plain (intermediate incidence), and 9 were in Montgomery County, Virginia (low incidence). Total acid-fast cells ranged widely between 280 to 5,367 per ml among the groundwaters, and with one exception showed no correlations or trends between regions of different incidence of human infection, or to total bacterial cell counts or colony-forming units. The exception was that the proportions of acid-fast cells relative to total cells were higher in the Georgia groundwaters. However, despite the relatively high auramine-O counts, few mycobacteria were recovered by culture. Of 12 wells yielding mycobacteria, 9 yielded rapidly growing and 4 slowly growing mycobacteria. Only one well in Montgomery County, Virginia (region of low incidence) yielded a MAIS isolate, albeit at low density. This research supports the conclusion that clean groundwaters are unlikely sources of MAIS infection in humans in the southeastern United States.