Risk Factors of Methicillin-Resistant Staphylococcus aureus Infection and Correlation With Nasal Colonization Based on Molecular Genotyping in Medical Intensive Care Units

Methicillin-resistant Staphylococcus aureus (MRSA) is a common and important cause of colonization and infection in medical intensive care units (ICU). The aim of this study was to assess association factors between MRSA nasal colonization and subsequent infections in medical ICU patients by clinical investigation and molecular genotyping. A prospective cohort observational analysis of consecutive patients admitted to medical ICUs between November 2008 and May 2010 at a tertiary teaching hospital were included. To detect MRSA colonization, the specimens from the nares were obtained within 3 days of admission to the ICU and again 1 week following admission to the ICU. Genetic relatedness for colonized and clinical isolates from each study patient with MRSA infection were analyzed and compared. A total of 1266 patients were enrolled after excluding 195 patients with already present MRSA infections. Subsequent MRSA infection rates were higher in patients with nasal colonization than in those without (39.1% versus 14.7%, respectively). Multivariate Poisson regression analysis demonstrated that nasal MRSA colonization (relative risk [RR]: 2.50; 95% confidence interval [CI]: 1.90–3.27; P< 0.001) was independent predictors for subsequent MRSA infections. History of tracheostomy, however, was a protective predictor in all patients (RR: 0.38; 95% CI: 0.18–0.79; P1⁄4 0.010) and in patients with MRSA nasal colonization (RR: 0.22; 95% CI: 0.55–0.91; n-Chung Hu, MD, ang, MD, u-Chering Huang, MD, PhD Methicillin-resistant S. aureus nasal colonization was significantly associated with subsequent MRSA infection among medical ICU patients. Previous MRSA infection was associated with subsequent MRSA infections, and history of tracheostomy associated with reducing this risk. Most MRSA isolates were healthcare-associated strains that were significantly correlated between nasal and clinical isolates. (Medicine 94(28):e1100) Abbreviations: CI = confidence interval, ICU = intensive care unit, MLST = multilocus sequence typing, MRSA = methicillin-resistant Staphylococcus aureus, MSSA = methicillin-susceptible Staphylococcus aureus, PCR = polymerase chain reaction, PFGE = pulsed-field gel electrophoresis, PVL = Pantone-Valentine leukocidin, RR = relative risk, SD = standard deviation. INTRODUCTION M ethicillin-resistant Staphylococcus aureus (MRSA) is a common and important cause of infection in the intensive care unit (ICU) setting. Preceding MRSA colonization is a risk factor for subsequent MRSA infections. The colonizing bacterial strains may serve as endogenous reservoirs for overt clinical infections or may spread to other patients. Several studies have demonstrated a link between S. aureus carriage and subsequent infection in continuous peritoneal dialysis patients, nonsurgical patients, critical neonates, and medical ICU patients. The routine MRSA surveillance to prevent MRSA infections among ICU patients, however, is still a controversial policy. Controversy also exists about eliminating nasal MRSA carriage to prevent consequent MRSA infections. It is important to confirm the linkage between nasal carriage and clinical MRSA isolates to develop the best strategy to avoid systemic infection by decolonization methods. In 2000, 53% to 83% of S. aureus isolates attributed to nosocomial infections in 12 Taiwanese major hospitals were resistant to methicillin. In our adult ICUs, MRSA accounted for 77% of nasal S. aureus isolates with a high colonization rate (up to 32%) during a surveillance study in 2010. A prospective cohort observational study of medical ICU patients was undertaken to examine MRSA nasal colonization status and the development of MRSA infection. Our research goals were to determine the clinical association between nasal carriage of MRSA and subsequent MRSA infections and to identify additional risk factors associated with MRSA infection. en nasal and clinical isolates was also ed-field gel electrophoresis (PFGE) and ping (MLST) analysis. www.md-journal.com | 1 MATERIALS AND METHODS Study Settings and Design Chang-Gung Memorial Hospital, Lin-Kuo branch, is a university-affiliated 3700-bed tertiary teaching hospital in northern Taiwan that provides healthcare ranging from primary to tertiary care. A prospective cohort observational analysis of consecutive patients admitted to the 2 medical ICUs (44 beds) between November 2008 and May 2010 was performed. The Institutional Review Board of Chang-Gung Memorial Hospital reviewed and approved the study (IRB No.: 96–0104B) and the requirement for written informed consent was waived. For patients with multiple medical ICU admissions, only the first admission was included in the analysis. Nasal surveillance specimens for MRSA were collected. To detect MRSA colonization, the specimens from the nares were obtained within 3 days of admission to the ICU and again 1 week following admission to the ICU. Methicillin-resistant S. aureus isolates recovered from clinical diagnostic samples (beyond survey culture specimens) submitted to the clinical microbiology laboratory were defined as clinical isolates. True MRSA infections were defined by the following criteria. Bloodstream infection required a positive blood culture. Pneumonia required a positive respiratory culture, a compatible chest radiograph with symptoms and signs of lower respiratory tract infection and a decision to treat. Urinary tract infection required a positive urine culture and either a decision to treat or the growth of >100,000 CFU/ml plus at least 50 leukocytes per high-power field. All other sites, including pleural effusion, ascites, skin, and soft tissue required a positive culture and a decision to treat. To identify potential risk factors for MRSA infection, the following data were collected from each patient: baseline demographics, characteristics, underlying and current diseases, clinical covariates, dates of previous and current hospitalizations, date of ICU admission, previous MRSA infection, already present MRSA infection, and subsequent MRSA infection. Previous infection was defined as MRSA infection diagnosed at least 2 weeks before the current hospitalization. Already present infection was defined as MRSA infection diagnosed during this hospitalization but before admission to medical ICU or within 24 hours after ICU admission.