Gentamicin resistant and sensitive strains of S. aureus. Factors affecting colonization and virulence for infants in a special care nursery.

During an eight month period in 1978, a large number of infants in a special care nursery at Bellevue Hospital, New York City, were found to carry a Staphylococcus aureus which was resistant to gentamicin. The records of 43 newborn infants who were admitted during this period of high prevalence were analyzed retrospectively for factors that might favor acquisition of gentamicin sensitive or resistant strains. It was found that neither sex nor administration of gentamicin or kanamycin played a significant role. Duration of stay was a major determinant of colonization, but there was no significant difference between the median stay of infants colonized with gentamicin sensitive or resistant strains. A life table analysis showed no difference in the rate at which gentamicin sensitive or resistant strains were acquired. As a group, staphylococci were acquired at the same rate as Gram negative rods and less rapidly than S. epidermidis. A review of all nosocomial staphylococcal infections recognized in the unit during 1977 and 1978 did not support a concern that there might be greater risk of serious infections during the months when gentamicin resistant strains of S. aureus were prevalent. Both sensitive and resistant strains appeared to be similar in virulence. Indeed, in this infant population, there were no differences in behavior between gentamicin resistant and sensitive strains of S. aureus.