Methicillin-Resistant Staphylococcus aureus (MRSA) Carriage in 10 Nursing Homes in Orange County, California

  Background: MRSA is a major pathogen in the hospital setting, but has not been extensively studied in nursing homes. Residents are frequently transferred between hospitals and nursing homes, but no practices are uniformly in place for MRSA contact precautions, screening, or decolonization in nursing homes, suggesting that these facilities may serve as reservoirs of MRSA.   Objective: To assess the extent of MRSA carriage in residents of 10 nursing homes in a large metropolitan area—Orange County, CA.   Methods: At each nursing home, we assessed nasal carriage of MRSA for 50 residents on admission and another 100 residents in a point prevalence screening. All isolates were processed for susceptibility to mupirocin and other antibiotics. We collected prior history of MRSA, single or shared room, and the nursing home day when the swab was collected. We obtained facility characteristics, including annual admissions, length of stay, percent male residents, percent residents <65yo, distribution of race and ethnicity, and percent insured by Medicaid.             We assessed predictors of point prevalent MRSA carriage, including individual and facility level characteristics, using bivariate tests and a multivariate regression model clustering by facility.   Results: We obtained 1,500 bilateral nares swabs among the 10 nursing homes. The median MRSA admission prevalence was 18% (range 8% to 31%) and median MRSA point prevalence was 30% (range 7% to 51%). Point prevalence burden exceeded admission burden in 8 of 10 facilities (see Figure). Across facilities, the median proportion of isolates non-susceptible to select antibiotics were: mupirocin 10% (range 0-17%), clindamycin 74% (38-83%), erythromycin 95% (84-100%), levofloxacin 98% (94-100%), rifampin 0% (0-14%), tetracycline 3% (0-17%) and trimethoprim-sulfamethoxazole 3% (0-17%). Predictors of carriage included: 1) prior history of MRSA (OR = 2.7, p<0.001); 2) residence in a facility with a high MRSA admission prevalence (3% increase in odds of MRSA positivity for each 1% increase in facility MRSA admission prevalence, p=0.05); and 3) residence in a facility with a high proportion of Hispanic residents (5% increase in odds of MRSA positivity for each 1% increase in percent Hispanic residents, p<0.001). The proportions of non-White or Medicaid insured residents were collinear with the proportion of Hispanic residents in a given nursing home, but were less strongly associated with MRSA positivity.

Conclusions: MRSA carriage in nursing homes varies widely, but can be extensive. In some nursing homes, carriage approaches 50%. In this county, risk of MRSA carriage among nursing home residents is associated with a prior history of MRSA along with residence in a nursing home with a high importation of MRSA carriers or a high prevalence of Hispanic residents.

Figure: MRSA Carriage on Admission and Point Prevalence Screening in 10 Nursing Homes.