Risk Factors For Methicillin-Resistant Staphylococcus Aureus Isolation From Serially Obtained Sputum In Patients Hospitalized With Pneumonia

Background: Several previous studies have reported risk factors for carriage of methicillin-resistant Staphylococcus aureus (MRSA) in nursing home residents and/or hospitalized patients. In contrast, risk factors for new acquisition of MRSA during hospitalization would be another important issue. Aim: To identify risk factors for isolation of MRSA from sputum in patients hospitalized with pneumonia. Objectives and Methods: Patients who admitted with pneumonia were prospectively enrolled from 2003 to 2012. Sputum samples were collected on days 1, 4, 7, 11, 14 of hospitalization and thereafter for bacterial culture. The cases where MRSA was first isolated within day 3 were defined as carriage on admission (MRSA carriage), and the cases where MRSA was first isolated after day 4 were defined as new acquisition after admission (MRSA acquisition). Statistical analysis was performed to investigate the factors associated with an isolation of MRSA. Results: MRSA was isolated in 167 of 1008 cases (carriage: 47 cases, acquisition: 120 cases). Multivariate analysis revealed that impairment in activities of daily living (ADL) before admission (odds ratio (OR), 2.92; 95% confidence interval (CI), 1.37–6.22) and prior hospitalization within the last 90 days (OR, 3.75; 95% CI, 1.90–7.41) were identified as risk for MRSA carriage, and ADL disability before admission (risk ratio (RR), 1.82; 95% CI, 1.17–2.84) and high pneumonia severity index (PSI) on admission (RR, 2.20; 95% CI, 1.37–3.65) as risk for MRSA acquisition. Conclusion: Several risk factors for isolation of MRSA from sputum in patients hospitalized with pneumonia were identified.