Epidemiology of Staphylococcus aureus colonization in nursing home residents

Abstract

Background: We sought to characterize the clinical and molecular epidemiologic characteristics of Staphylococcus aureus colonization (especially extranasal colonization) and to determine the extent to which community-associated methicillin-resistant S. aureus (MRSA) has emerged in community nursing homes.

Methods: The study enrolled a total of 213 residents, with or without an indwelling device, from 14 nursing homes in southeastern Michigan. Samples were obtained from the nares, oropharynx, groin, perianal area, wounds, and enteral feeding tube site. Standard microbiologic methods were used to identify methicillin-susceptible S. aureus and MRSA. Molecular epidemiologic methods included pulsed-field gel electrophoresis, PCR detection of Panton-Valentine leukocidin, and SCCmec and agr typing.

Results: One hundred thirty-one residents (62%) were colonized with S. aureus (MRSA colonization in 86). S. aureus colonization occurred in 80 (76%) of 105 residents with indwelling devices and in 51 (47%) of 108 residents without indwelling devices (P<.001). Of the 86 residents who were colonized with MRSA, nares culture results were positive for only 56 (65%). Residents with devices in place were more likely to be colonized at multiple sites. Eleven different strains of MRSA were identified by pulsed-field gel electrophoresis. Seventy-three residents (85%) were colonized with hospital-associated SCCmec II strains, and 8 (9%) were colonized with community-associated SCCmec IV strains, 2 of which carried Panton-Valentine leukocidin.

Conclusions: Extranasal colonization with MRSA is common among nursing home residents-particularly among residents with an indwelling device. We documented the emergence of community-associated SCCmec IV MRSA strains in the community nursing home setting in southeastern Michigan.

Figure 1

Frequency of colonization at multiple sites with methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) among community nursing home residents.

Figure 2

PFGE-based dendrogram showing genetic relatedness among representative methicillin-resistant Staphylococcus aureus (MRSA) strains recovered from 40 community nursing home residents. Of 86 residents colonized with MRSA, 73 were colonized with SCCmec II, 8 were colonized with SCCmec IV, and 5 were colonized with mecA, ccr 4. PVL, Panton-Valentine leukocidin.