Staphylococcus aureus bacteremia after median sternotomy: clinical utility of blood culture results in the identification of postoperative mediastinitis

Abstract

Background: Mediastinitis is a complication of coronary artery bypass graft surgery (CABG) that can be difficult to diagnose. This study evaluated the utility of blood culture results in identifying patients with mediastinitis.

Methods and results: All unique patients undergoing CABG at our institution over a 60-month study period (n=5500) and all blood cultures performed on these patients <or=90 days after CABG were identified. Mediastinitis was identified by prospective active infection control surveillance. Eight hundred fifty-five (15.5%) patients had >or=1 blood culture drawn within 90 days of CABG. Mediastinitis occurred in 46 of 60 (76.7%) patients with blood cultures positive for Staphylococcus aureus, 15 of 126 (11.9%) patients with blood cultures positive for other pathogens, 37 of 669 (5.5%) patients with blood cultures with no growth, and 44 of 4645 (0.9%) patients with no blood cultures obtained. The isolation of S aureus from even 1 blood culture drawn after <or=90 days of CABG was strongly associated with mediastinitis (likelihood ratio [LR], 25; 95% CI, 14.7 to 44.4). Bacteremia attributable to other organisms did not alter pretest suspicion for mediastinitis (LR, 1.0; 95% CI, 0.6 to 1.7). Patients with negative blood cultures were less likely to have mediastinitis (LR, 0.45; 95% CI, 0.35 to 0.58). The association between S aureus bacteremia and mediastinitis remained highly significant when all unique patients undergoing CABG were analyzed in a logistic regression model and when a case-control analysis was used to evaluate patients with >or=1 blood culture obtained after CABG.

Conclusions: Among patients with blood cultures drawn after CABG, S aureus bacteremia strongly suggests the presence of mediastinitis.