Background Methicillin-resistant Staphylococcus aureus is a cause of lower respiratory tract infections, particularly health care-and ventilator-associated pneumonia. Although many health systems use nasal screening for this microorganism for infection control, correlation between nasal carriage of the organism and development of infections due to it is not clear. Methods Records of patients admitted to medical intensive care between January 1, 2011, and December 31, 2012, were reviewed retrospectively. Patients' data were included if the patients were 18 years or older, satisfied clinical criteria for pneumonia, and had both nasal swabbing and culturing of respiratory specimens within 24 hours of admission. Results A total of 165 patients met the inclusion criteria. Most had either community-acquired or health care-associated pneumonia. Of the 28 patients with a nasal swab positive for methicillinresistant S aureus, 8 (4.8%) also had respiratory tract cultures positive for the microorganism. Among the 165 patients, 2 (1.2%) had negative nasal swabs but positive respiratory cultures. Sensitivity and specificity of nasal colonization with methicillinresistant S aureus for subsequent infection with the pathogen were 80% and 87.1%, respectively; positive and negative predictive values were 28.6% and 98.5%, respectively. Conclusions Nasal screening for methicillin-resistant S aureus may be a valuable tool for de-escalation of empiric therapy targeted to the organism, especially in patients admitted for severe community-acquired or health care-associated pneumonia. The high negative predictive value suggests that patients with a negative nasal swab most likely do not have a lower respiratory tract infection caused by the organism.

OBJECTIVES: The primary endpoint was to determine the sensitivity and specificity of the bronchoalveolar lavage Gram stain in predicting culture results. Secondary endpoints included determining the proportion of Gram stains from bronchoalveolar lavages that accurately identify culture isolates and the duration of antibiotic treatment before bronchoalveolar lavage collection. DESIGN: Retrospective, observational study. SETTING: Four ICUs at a single academic medical center. SUBJECTS: Patients at least 18 years old admitted to an ICU with a diagnosis of pneumonia, collection of a bronchoalveolar lavage sample, and receipt of antibiotics. MEASUREMENTS AND MAIN RESULTS: Two-hundred five isolates were included. Gram stains for Gram-positive and Gram-negative isolates showed high specificity, 97.3% and 100%, respectively, but lower sensitivity at 61.9% and 54.2%, respectively. The positive predictive value and negative predictive value were 77.2% and 95.7% for Gram-positive isolates and 100% and 84.4% for Gram-negative isolates, respectively. Gram stains correctly identified isolates on the bronchoalveolar lavage culture in 61.9% of Gram-positive organisms and in 54.2% of Gram-negative organisms. CONCLUSIONS: Gram stains accurately identified causative organisms in a limited number of patients making the utility of the Gram stain an uncertain modality for predicting causative respiratory pathogens from bronchoalveolar lavage samples.

In this study, we aimed to develop a locally derived clinical prediction model for Pseudomonas -mediated pneumonia. Utilizing a locally validated prediction score may help direct therapeutic management and be generalizable to other clinical settings and similar populations for the selection of appropriate antimicrobial coverage when data are lacking.

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