Persistence of a multiresistant clone of Staphylococcus epidermidis in a neonatal intensive-care unit for a four-year period.

A cluster of cases of Staphylococcus epidermidis bacteremia in a neonatal intensive-care unit (NICU) during 1991 raised the question of whether these infections were caused by a single strain. Sixty-seven isolates of S. epidermidis from blood cultures of 56 neonates treated in the NICU between 1986 and 1992 and 54 control strains from other patients with bacteremia were characterized by three typing methods: antibiogram, plasmid profile, and ribotype. Plasmid profiles and ribotype patterns indicated that 11 (16%) of the 67 episodes of S. epidermidis bacteremia in the NICU were caused by a single strain. Although this epidemic strain did not account entirely for the increase in the incidence of bacteremia in the NICU, it did persist for 4 years during the study period. Other clones responsible for smaller outbreaks were also found. These results suggest that S. epidermidis cross-infections are very common in the NICU setting.