Impact of methicillin-resistant Staphylococcus aureus on the incidence of nosocomial staphylococcal infections.

MRSA strains have become increasingly prevalent in the United States and are now an important cause of nosocomial infections in many large, medical school-affiliated hospitals. In affected institutions, from a few percent to 50% of all hospital-acquired S aureus infections are caused by MRSA strains. It has been suggested that the overall incidence of nosocomial S aureus infections may not increase in hospitals where MRSA strains have become epidemic or endemic and that MRSA strains merely replace methicillin-susceptible strains as a cause of hospital-acquired infections. Several recent studies lend support to this theory. Thompson et al [1] reported that the overall incidence of nosocomial S aureus-associated bacteremias and postoperative wound infections in a university hospital did not increase during a period when MRSA strains caused a significantly greater proportion of such infections. Similarly, Linnemann et al [2] found that the overall incidence of nosocomial S aureus-associated bacteremias did not change during a four-year period when the incidence of MRSA-associated bacteremias increased appreciably. At the University of Mississippi Medical Center, MRSA strains have been recovered from patients with increased frequency since an outbreak of MRSA infections occurred in the burn unit in June 1979 [3]. Continuing surveillance has revealed that the incidence of nosocomial MRSA infections was significantly higher in 1980-1982 than during 1979 (P = 0.002 by Mann-Whitney U test). MRSA strains accounted for 11% of nosocomial S aureus infections in 1979, 38% in 1980, 50% in 1981, 36% in 1982, and 32% in early 1983.(ABSTRACT TRUNCATED AT 250 WORDS)