BACKGROUND:In the middle of October 2011, the Hygiene Department of Caen University Hospital suspected an outbreak of surgical site infections (SSI) after open-heart operations with an unusually high proportion of microorganisms belonging to the Enterobacteriaceae family. The attack rate was 3.8%, significantly different (p = 0.035) from the attack rate of 1.2% in 2010 over the equivalent period. A case-control study was conducted to search specifically for risk factors for Enterobacteriaceae infections after median sternotomy in cardiac patients. METHODS:Case patients were defined retrospectively as patients with superficial or deep surgical site infection with Enterobacteriaceae within 30 days of median sternotomy. Four control patients were selected per case patient from patients matched for date of operation (± 15 days) and European System for Cardiac Operative Risk Evaluation (<5, [5-10], >10). RESULTS:Univariate analysis identified the following risk factors: inappropriate skin preparation on the morning of the intervention (p = 0.046), use of vancomycin (p = 0.030), and number of sternotomy dressings (p = 0.033). A multivariate logistic regression analysis found that vancomycin use was independently associated with an increased risk of postoperative SSI with Enterobacteriaceae (p = 0.019; odds ratio = 7.4). CONCLUSIONS:Although vancomycin is known to be effective for preventing infection with methicillin-sensitive organisms, our results suggest that it was associated with a risk for the development of SSI with gram-negative organisms after median sternotomy. This study led to a multidisciplinary meeting that defined new guidelines for prophylactic antibiotic therapy before open-heart operations.