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

Ampicillin-resistant enterococci (ARE) have recently emerged as clinical pathogens in Sweden. Between 1991 and 1995 the incidence of ARE among enterococcal isolates at Uppsala University Hospital increased from 0.5% to 8.1%. Shedding of ARE from infected cases and risk factors for infection with ARE were studied during a period of 7 months for 38 ARE cases and 38 controls with ampicillin-susceptible enterococci. ARE cases had longer mean duration of hospitalization than controls (29 d vs. 15 d; p = 0.002). In univariate analysis other risk factors for infection with ARE were found to be prior therapy with > 2 antimicrobials (odds ratio [OR] 3.3; 95% confidence interval [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 carriers of ARE were found to be shedding ARE to the environment, compared to 2 of 12 non-skin carriers (p = 0.03). Pulsed-field gel electrophoresis suggested multifocal origin of the majority of the infecting ARE strains. Non-recognized fecal colonization and silent spread of ARE among many patients and over a prolonged time period is suggested to be the main explanation for the increase of ARE infections in our hospital. Infection control measures focusing on protecting patients at high risk for ARE infections and further efforts to optimize antimicrobial use are proposed.