The Enterococcus has become an important nosocomial pathogen despite its low virulence. From 1986 to 1989, the National Nosocomial Infections Surveillance System (NNIS) reported enterococci to be the third most common pathogen associated with bloodstream infections and the second most commonly isolated pathogen overall. This is due in part to the organism's ubiquitous nature and inherent antimicrobial resistance.
Enterococcus faecalis is found in the stool of virtually all adults at concentrations in excess of 106 colony-forming units/g. Enterococcus faecium, the second most common species causing human infection, is found at lesser concentrations in the stool of approximately 25% of healthy adults. Enterococci also can be isolated from the mouth, anterior urethra, groin, and vagina.