Risk Factors for Methicillin-Resistant Staphylococcus aureus Carriers in the Intensive Care Unit: A Single-Center, Retrospective Cohort Study in Japan.

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a common pathogen in the intensive care unit (ICU). Active surveillance cultures (ASCs) for MRSA are often performed in ICUs; however, they may not be optimal in ICUs with a low MRSA prevalence. This study aims to determine the risk factors of MRSA carriage in the ICU and develop a clinical predictive model to optimize the screening process. Methods: All patients who were admitted to the ICU between April 2015 and August 2022 were retrospectively included in this study. At the time of ICU admission, all patients underwent MRSA screening using nasal ASCs. Based on the screening results, patients were categorized into MRSA-positive and MRSA-negative groups. Patients' characteristics were evaluated to determine the prevalence of MRSA and the risk factors. Cost analysis was conducted based on the risk factors identified by our analysis. Results: Of the 3927 ICU patients included, 133 (3.4%) were MRSA-positive. Multivariate analyses showed that risk factors for MRSA carriage were age ≥ 50 years (odds ratio [OR]: 2.11), history of hospitalization within a year (OR: 1.50), and ICD-10 codes classification I, IV, and XII (OR: 4.98). Screening patients based on at least one of the risk factors exhibited high sensitivity (96.9%) to identifying MRSA carriage and could reduce ASC overall costs by 10.9%, equivalent to $4686. Conclusion: This study suggests that universal ASCs to detect MRSA may not be optimal in ICU settings with a low prevalence of MRSA. Targeted screening based on risk factors may reduce the volume and cost of MRSA screening. Prospective multicenter studies are warranted to validate these findings and to assess the generalizability of the proposed screening strategy.