Ampicillin-resistant enterococci in a Swedish university hospital: Nosocomial spread and risk factors for infection

Ampicillin-resistant enterococci (ARE) have recently emerged as clinical pa thogens in Sweden. Between 1991 and 1995 the incidence of ARE among enteroc occal isolates at Uppsala University Hospital increased from 0.5% to 8.10%. Shedding of ARE from infected cases and risk factors for infection with AR E were studied during a period of 7 months for 38 ARE cases and 38 controls with ampicillin-susceptible enterococci. ARE cases had longer mean duratio n of hospitalization than controls (29 d vs. 15 d; p = 0.002). In univariat e analysis other risk factors for infection with ARE were found to be prior therapy with > 2 antimicrobials (odds ratio [OR] 3.3; 95% confidence inter val [CI] 1.2-9.5), > 4,weeks of antimicrobial therapy (OR 6.9; CI 1.8-28.3) and cephalosporin therapy (OR 9.1; CI 2.6-33.7). Fourteen of 26 skin carri ers of ARE mere found to be shedding ARE to the environment, compared to 2 of 12 non-skin carriers p = 0.03). Pulsed-field gel electrophoresis suggest ed multifocal origin of the majority of the infecting ARE strains. Non-reco gnized fecal colonization and silent spread of ARE among many patients and over a prolonged time period is suggested to be the main explanation for th e increase of ARE infections in our hospital. Infection control measures fo cusing on protecting patients at high risk for ARE infections and further e fforts to optimize antimicrobial use are proposed.