Study: Community MRSA strains beset nursing homes after first setting up in hospitals

January 12th, 2015

There is growing evidence that many nursing homes have a high prevalence of community-associated strains of methicillin-resistant Staphylococcus aureus (CA-MRSA) and contribute to regional spread among healthcare facilities. In a new study of more than 20 nursing homes in California, the authors found that CA-MRSA – primarily the USA300 strain -- was present in all but two of the facilities.(1) The level of CA-MRSA prevalence varied greatly, reaching nearly half of MRSA carriers in one facility.

As infection preventionists are aware, CA-MRSA is a growing cause of invasive disease, including bloodstream infections, abscesses, and pneumonia. Since most nursing home residents are admitted directly from hospitals, importation of CA-MRSA may increase in nursing homes as CA-MRSA increases in hospitals, the authors noted. However, this has been akin to a chicken-egg argument over the years, and the study does not attempt to connect MRSA data from area hospitals to the nursing homes. That said, nursing home residents also have increased risk factors for MRSA, including diabetes, long-term use of indwelling devices, and inability to perform activities of daily living.

Researchers at the University of California, Irvine assessed the frequency of CA-MRSA carriage among residents in a convenience sample of 22 of the 72 nursing homes in Orange County, California, during the period October 2008–May 2011. Strains were found by swabbing the noses of 100 residents in each nursing home at a single visit and up to another 100 additional swabs from newly admitted residents. Of the MRSA-positive swabs, 25 percent (208/824) were positive for CA-MRSA. The study also found CA-MRSA was present in 20 out of 22 nursing homes tested.

“Community-type strains first arose among healthy community members without exposure to the healthcare system and have steadily infiltrated many hospitals,” said Courtney R. Murphy, PhD, the study’s lead researcher. “We believe these at-risk facilities could benefit from further infection control interventions, such as enhanced environmental cleaning or skin decolonization.”

CA-MRSA was more common in nursing homes in which a larger percent of residents were under the age of 65 years. In the community, CA-MRSA frequently infects children and younger adults, particularly in high-contact settings, such as child care centers, sports activities, and the military. In turn, younger nursing home residents may be more mobile and better able to interact with others, increasing their risk of MRSA acquisition.

The strain also was also less common at admission compared to later sampling, suggesting CA-MRSA may be transmitted among residents. Infection control strategies to prevent transmission may need to be tailored to the nursing home setting, since the goal of encouraging social interaction in nursing homes presents unique challenges for infection control compared to hospitals.

CA-MRSA was also associated with facilities with more Hispanic residents. This finding was not associated with resident socioeconomic status or low-resource nursing homes; however it may reflect cultural or genetic differences associated with increased risk factors, the researchers concluded.

Reference

1. Murphy CR, Hudson LO, Spratt BG. Predicting High Prevalence of Community Methicillin-Resistant Staphylococcus aureus Strains in Nursing Homes. Infect Control Hosp Epi 2013;34:325-328