title: Using MRSA Screening Tests To Predict Methicillin Resistance in Staphylococcus aureus Bacteremia.
abstract: Bloodstream infections with Staphylococcus aureus are clinically significant and are often treated with empirical methicillin resistance (MRSA, methicillin-resistant S. aureus) coverage. However, vancomycin has associated harms. We hypothesized that MRSA screening correlated with resistance in S. aureus bacteremia and could help determine the requirement for empirical vancomycin therapy. We reviewed consecutive S. aureus bacteremias over a 5-year period at two tertiary care hospitals. MRSA colonization was evaluated in three ways: as tested within 30 days of bacteremia (30-day criterion), as tested within 30 days but accounting for any prior positive results (ever-positive criterion), or as tested in known-positive patients, with patients with unknown MRSA status being labeled negative (known-positive criterion). There were 409 S. aureus bacteremias: 302 (73.8%) methicillin-susceptible S. aureus (MSSA) and 107 (26.2%) MRSA bacteremias. In the 167 patients with MSSA bacteremias, 7.2% had a positive MRSA test within 30 days. Of 107 patients with MRSA bacteremia, 68 were tested within 30 days (54 positive; 79.8%), and another 21 (19.6%) were previously positive. The 30-day criterion provided negative predictive values (NPV) exceeding 90% and 95% if the prevalence of MRSA in S. aureus bacteremia was less than 33.4% and 19.2%, respectively. The same NPVs were predicted at MRSA proportions below 39.7% and 23.8%, respectively, for the ever-positive criterion and 34.4% and 19.9%, respectively, for the known-positive criterion. In MRSA-colonized patients, positive predictive values exceeded 50% at low prevalence. MRSA screening could help avoid empirical vancomycin therapy and its complications in stable patients and settings with low-to-moderate proportions of MRSA bacteremia.
authors.affiliation: Department of Medicine, McGill University Health Centre, Montreal, Quebec, Canada guillaume.butler-laporte@mail.mcgill.ca.
authors.forename: Guillaume
authors.identifier: 0000-0001-5388-0396
authors.initials: G
authors.lastname: Butler-Laporte
authors.affiliation: Department of Microbiology, McGill University Health Centre, Montreal, Quebec, Canada.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Cheng
authors.affiliation: École Polytechnique de Montréal, Montréal, Canada.
authors.forename: Alexandre P
authors.initials: AP
authors.lastname: Cheng
authors.affiliation: Department of Medicine, McGill University Health Centre, Montreal, Quebec, Canada.|Clinical Practice Assessment Unit, McGill University Health Centre, Montreal Quebec, Canada.
authors.forename: Emily G
authors.initials: EG
authors.lastname: McDonald
authors.affiliation: Department of Medicine, McGill University Health Centre, Montreal, Quebec, Canada.|Department of Microbiology, McGill University Health Centre, Montreal, Quebec, Canada.|Clinical Practice Assessment Unit, McGill University Health Centre, Montreal Quebec, Canada.
authors.forename: Todd C
authors.initials: TC
authors.lastname: Lee
mesh_terms: D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D016470:Bacteremia / Q000188:drug therapy* / Q000382:microbiology; D006801:Humans; D008712:Methicillin / Q000627:therapeutic use*; D016106:Methicillin Resistance / Q000187:drug effects*; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development; D008826:Microbial Sensitivity Tests; D011237:Predictive Value of Tests; D011792:Quebec; D012189:Retrospective Studies; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000382:microbiology; D062606:Tertiary Care Centers; D014640:Vancomycin / Q000627:therapeutic use
chemical_list: D000900:Anti-Bacterial Agents; D014640:Vancomycin; D008712:Methicillin