Risk factors of nosocomial pneumonia caused by methicillin-resistant Staphylococcus aureus

Background and objective: To include a specific antibiotic in the empiric therapy, it is necessary to predict when a nosocomial pneumonia (NP) is caused by methicillin-resistant Staphylococcus aureus (MRSA). We have developed a model for the prediction of the probability of a NP being caused by MRSA, when the carrier status and the microbiological diagnosis are unknown. Patients and methods: A retrospective case-control study (1999-2005) was designed. A univariate and multivariate logistic regression was performed to identify the risk factors for suffering a NP due to MRSA. Demographic factors, related to hospitalization, immunosuppression or neutropenia, to medication and severity were included. Results: Three hundred and sixty three patients (121 cases and 242 controls) were studied. The final model of multivariate logistic regression included an age > 14 years (OR 7.4, CI 95% 1.5-37.4, P < .015), NP appearance > 6 days after admittance (OR 4.1, CI 95% 2.4-7,1, P < .001), NP development excluding summers (OR 2.5, CI 95% 1.2-5.2, P < .015), respiratory diseases (OR 4.9, CI 95% 1.5-15.8, P < .007) and multilobar involvement (OR 4, CI 95% 2.3-7.2, P < .001). The probability of developing a pneumonia due to MRSA was studied for each of the possible combinations and subsequently classified in minor and major criteria. Conclusions: MRSA coverage should be included in the empirical treatment of NP when: a) an adult patient (> 14 years old) presents, at least, 2 major criteria or 1 major criterion together with 2 minor criteria, and b) a patient < 14 years-old has 2 major criteria as well as 2 minor criteria. (C) 2011 Elsevier Espana, S.L. All rights reserved.