Epidemiology of infection by nontuberculous mycobacteria

The past 10 years have seen enormous increases in the number of nontuberculous mycobacterial infections, principally in patients with AIDS. Today, there is heightened awareness of the importance of nontuberculous mycobacterial infections. In addition to the increase in the number of infections with known mycobacteria (e.g, Mycobacterium avium), new species (e.g., Mycobacterium genavense) have been identified some by nonconventional methods. For the most part, nontuberculous mycobacteria are opportunistic pathogens whose normal habitat is natural (e.g., livers, swamps, and soils) and human-influenced (e.g, drinking water) environments. Focus has been on identification of sources and routes of transmission. Sources have been identified for some (e.g, M. avium and Mycobacterium xenopi) but not others (e.g, Mycobacterium haemophilum). Physiological studies have led to descriptions of the ecology and epidemiology for some species. Some grow in natural or potable water. All strains tested have been resistant to standard methods of disinfection. Consequently, they are found in drinking water. Characteristics that enhance environmental survival may also promote survival in infected animals Tools for genetic analysis of nontuberculous mycobacteria (e.g, PCR) have led to identification of antibiotic resistance genes and to development of molecular markers for epidemiological studies. Molecular markers have confirmed the wide heterogeneity of natural mycobacterial populations and have been used to show the genetic identity of environmental and patient isolates.