Molecular Epidemiology of Methicillin-Resistant Staphylococcus aureus (MRSA) among Patients Admitted to Adult Intensive Care Units: The STAR*ICU Trial

BACKGROUND. The multicenter, cluster-randomized Strategies to Reduce Transmission of Antimicrobial Resistant Bacteria in Intensive Care Units (STAR(star)ICU) trial was performed in 18 U. S. adult intensive care units (ICUs). It evaluated the effectiveness of infection control strategies to reduce the transmission of methicillin-resistant Staphylococcus aureus (MRSA) colonization and/or infection. Our study objective was to examine the molecular epidemiology of MRSA and assess the prevalence and risk factors for community acquired (CA)-MRSA genotype nasal carriage at the time of ICU admission. METHODS. Selected MRSA isolates were subjected to molecular typing using pulsed-field gel electrophoresis. RESULTS. Of 5,512 ICU patient admissions in the STAR(star)ICU trial during the intervention period, 626 (11%) had a nares sample culture result that was positive for MRSA. A total of 210 (34%) of 626 available isolates were selected for molecular typing by weighted random sampling. Of 210 patients, 123 (59%) were male; mean age was 63 years. Molecular typing revealed that 147 isolates (70%) were the USA100 clone, 26 (12%) were USA300, 12 (6%) were USA500, 8 (4%) were USA800, and 17 (8%) were other MRSA genotypes. In a multivariate analysis, patients who were colonized with a CA-MRSA genotype (USA300, USA400, or USA1000) were less likely to have been hospitalized during the previous 12 months (PR [prevalence ratio], 0.39 [95% confidence interval (CI), 0.21-0.73]) and were less likely to be older (PR, 0.97 [95% CI, 0.95-0.98] per year) compared with patients who were colonized with a healthcare-associated (HA)-MRSA genotype. CONCLUSION. CA-MRSA genotypes have emerged as a cause of MRSA nares colonization among patients admitted to adult ICUs in the United States. During the study period (2006), the predominant site of CA-MRSA genotype acquisition appeared to be in the community. Infect Control Hosp Epidemiol 2011; 32(11): 1057-1063