A Clinical History of Methicillin-Resistant Staphylococcus aureus Is a Poor Predictor of Preoperative Colonization Status and Postoperative Infections

Abstract

Objective.In the absence of established methicillin-resistant Staphylococcus aureus (MRSA) screening programs, many centers use a history of a positive culture or a nasal screen as a surrogate for preoperative MRSA colonization status. We aimed to evaluate the test characteristics of these surrogates.Design.Retrospective cohort study.Participants.Veterans Affairs Boston Healthcare System surgical patients with a preoperative nasal MRSA polymerase chain reaction (PCR) screen.Methods.We assessed the performance of a history of a MRSA-positive culture or a positive nasal MRSA PCR screen during the year prior to surgery for predicting the preoperative nasal PCR screen result. The associations between MRSA history and postoperative outcomes, including MRSA cultures and infections, were also evaluated.Results.Among 4,238 patients, a positive MRSA culture history had a sensitivity of 19.7% (95% confidence interval [CI], 15.4%–24.8%) and positive predictive value of 57.3% for the preoperative nasal MRSA status. The specificity of MRSA culture history was 99% (95% CI, 98.5%–99.2%). Prior-year nasal MRSA screen results had similar test characteristics. A history of a MRSA-positive culture was associated with an increased risk of postoperative MRSA-positive cultures (risk ratio [RR], 3.54 [95% CI, 1.70–7.37], P< .001) but not of infections (RR, 1.71 [95% CI, 0.58–5.01]), after adjustment for preoperative nasal MRSA status, vancomycin surgical prophylaxis, surgical scrub, and age.Conclusions.A history of a MRSA-positive culture and a positive nasal PCR screen are poor surrogate markers of preoperative colonization status, missing at least 70% of MRSA-colonized patients. Prior-year history is also not independently associated with MRSA-related postoperative infections. Strong consideration should be given to preoperative MRSA screening in patients at high risk for surgical complications.