SAN DIEGO — Community-associated methicillin-resistant Staphylococcus aureus genotypes have emerged as a cause of MRSA nares colonization among patients admitted to adult ICUs in the United States.
In addition, patients with a history of previous hospitalization and those older in age were significantly less likely to be colonized with community-associated MRSA (CA-MRSA) genotypes.
Those are the key findings from an effort to examine the molecular epidemiology and assess the prevalence of and risk factors for CA-MRSA genotype carriage among patients admitted to adult ICUs.
The molecular epidemiology of MRSA in the health care setting is incompletely defined, Dr. Henry M. Blumberg said at the annual meeting of the Society for Healthcare Epidemiology of America.
Dr. Blumberg and his associates studied 5,512 adult ICU visits at 18 academic medical centers that participated in the STAR-ICU (Strategies to Reduce Transmission of Antimicrobial-Resistant Bacteria in Intensive Care Units) trial. STAR-ICU, a National Institutes of Health-funded trial, is designed to evaluate the effectiveness of a package of infection control strategies focused on active surveillance cultures and barrier precautions in reducing transmission of MRSA and vancomycin-resistant enterococci (VRE) among adults in ICUs for 3 or more days.
CA-MRSA genotypes were defined as USA300, USA400, and USA1000 while health care-associated MRSA genotypes (HA-MRSA) were defined as USA100, USA200, USA500, USA600, USA800, the epidemic strain EMRSA-15, and the Brazilian clone.
Of the 5,512 patients, 626 (11%) had a positive culture for MRSA, reported Dr. Blumberg, professor of medicine and epidemiology in the division of infectious diseases at Emory University, Atlanta.
Of 210 isolates available for molecular typing, 70% were the USA100 clone, 12% were USA300, 6% were USA500, 4% were USA800, 3% were the Brazilian clone, 2% were USA600, 1% were USA1000, 1% were USA-200, 0.5% were USA400, and 0.5% were EMRSA-15.
Overall, 14% of patients had CA-MRSA colonization.
Univariate analysis revealed that compared with patients colonized with HA-MRSA genotypes, those colonized with CA-MRSA genotypes were significantly younger (51 years vs. 65 years), significantly less likely to have been hospitalized in the previous 12 months (47% vs. 74%), and significantly less likely to have a history of MRSA or VRE colonization or infection (13% vs. 37%). Multivariate analysis revealed similar findings.
“These findings suggest that the predominant site of MRSA acquisition remains in the community,” Dr. Blumberg concluded.
He said he had no conflicts of interest to disclose.