Risk factors associated with methicillin-resistant Staphylococcus aureus isolation from serially collected sputum samples of patients hospitalized with pneumonia

Risk factors associated with the new detection of methicillin-resistant Staphylococcus aureus (MRSA) during hospitalization remain unclear. This study aimed to identify risk factors associated with MRSA isolation from the sputum of patients admitted with pneumonia, during their hospitalization. Patients were prospectively enrolled from 2003 to 2012. Sputum samples were collected for bacterial cultures on days 1, 4, 7, 11, and 14 of hospitalization and thereafter. Cases of MRSA first isolated from sputum obtained before day 4 were defined as “carriage on admission.” Cases of MRSA first isolated on day 4 and thereafter, were defined as “new detection after admission.” Statistical analysis was used to investigate the risk factors associated with MRSA isolation. MRSA was isolated from 167 of 1,008 patients (carriage: 47; new detection: 120). Multivariate analysis revealed that the risk factors for MRSA carriage were activities of daily living (ADL) disability prior to admission (odds ratio [OR], 2.92; 95% confidence interval [CI], 1.37–6.22) and hospitalization within the previous 90 days (OR, 3.75; 95% CI, 1.90–7.41). ADL disability prior to admission (risk ratio [RR], 1.82; 95% CI, 1.17–2.84) and a high pneumonia severity index score upon admission (RR, 2.20; 95% CI, 1.37–3.65) were risk factors for new detection of MRSA. Several risk factors were found to be associated with MRSA carriage and/or its new detection, based on the sputum samples from patients admitted with pneumonia. These factors may be indicators for selective surveillance and the early implementation of infection control measures.