title: Predictive value of methicillin-resistant Staphylococcus aureus (MRSA) nasal swab PCR assay for MRSA pneumonia.
abstract: Pneumonia due to methicillin-resistant Staphylococcus aureus (MRSA) is associated with poor outcomes and frequently merits empirical antibiotic consideration despite its relatively low incidence. Nasal colonization with MRSA is associated with clinical MRSA infection and can be reliably detected using the nasal swab PCR assay. In this study, we evaluated the performance of the nasal swab MRSA PCR in predicting MRSA pneumonia. A retrospective cohort study was performed in a tertiary care center from January 2009 to July 2011. All patients with confirmed pneumonia who had both a nasal swab MRSA PCR test and a bacterial culture within predefined time intervals were included in the study. These data were used to calculate sensitivity, specificity, positive predictive value, and negative predictive value for clinically confirmed MRSA pneumonia. Four hundred thirty-five patients met inclusion criteria. The majority of cases were classified as either health care-associated (HCAP) (54.7%) or community-acquired (CAP) (34%) pneumonia. MRSA nasal PCR was positive in 62 (14.3%) cases. MRSA pneumonia was confirmed by culture in 25 (5.7%) cases. The MRSA PCR assay demonstrated 88.0% sensitivity and 90.1% specificity, with a positive predictive value of 35.4% and a negative predictive value of 99.2%. In patients with pneumonia, the MRSA PCR nasal swab has a poor positive predictive value but an excellent negative predictive value for MRSA pneumonia in populations with low MRSA pneumonia incidence. In cases of culture-negative pneumonia where initial empirical antibiotics include an MRSA-active agent, a negative MRSA PCR swab can be reasonably used to guide antibiotic de-escalation.
authors.affiliation: Division of Internal Medicine, Maricopa Medical Center, Phoenix, Arizona, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Dangerfield
authors.forename: Andrew
authors.initials: A
authors.lastname: Chung
authors.forename: Brandon
authors.initials: B
authors.lastname: Webb
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Seville
mesh_terms: D000368:Aged; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D054796:Drug Dosage Calculations; D005260:Female; D006801:Humans; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000235:genetics / Q000302:isolation & purification*; D008826:Microbial Sensitivity Tests; D009296:Nasal Cavity / Q000382:microbiology*; D011023:Pneumonia, Staphylococcal / Q000175:diagnosis* / Q000188:drug therapy / Q000382:microbiology; D016133:Polymerase Chain Reaction / Q000706:statistics & numerical data*; D011237:Predictive Value of Tests; D012189:Retrospective Studies
chemical_list: D000900:Anti-Bacterial Agents