Clinical and molecular epidemiology of nursing home-associated Staphylococcus aureus bacteremia.

BACKGROUND AND OBJECTIVES: Although nursing home residents who have Staphylococcus aureus bacteremia (SAB) have been included in large studies of this infection, there are no published descriptions of SAB solely in nursing home residents. The objectives were to describe the clinical and molecular epidemiology of SAB in nursing home residents admitted to one hospital.

METHODS: This was a retrospective review of hospital medical records of nursing home residents from 22 separate facilities who had SAB and were admitted to a specialty unit at one hospital from 1997 to 2003.

RESULTS: For the seven-year study period, 39 episodes of SAB were identified; 15 were due to methicillin-susceptible S. aureus (MSSA) and 24 were due to methicillin-resistant S. aureus (MRSA). The incidence of SAB among all residents admitted to the specialty unit increased by more than eightfold primarily because of an increased incidence of bacteremia due to MRSA. The most common identified source was the urinary tract (18% of all episodes) but for 17 (44%) episodes, no focus was identified. Hospital mortality was 28% with all deaths occurring within 15 days of admission. Analysis of the MRSA strains by pulsed-field gel electrophoresis revealed that two pulsed-field types predominated when compared with the CDC national database: USA100- (N = 13) and USA 800-like strains (N = 7).

CONCLUSIONS: In the study population there was a substantial increase in incidence of SAB over a 7-year period due almost exclusively to an increased occurrence of MRSA. Hospital strains of MRSA predominated, as one would expect. Mortality was high but complications were low among survivors. These findings have important implications for choosing empiric antibiotic therapy in nursing home residents who have suspected S. aureus infection.