Center-level variation in infection rates after coronary artery bypass grafting

Abstract

Background: Health-care-acquired infections (HAIs) are a leading cause of morbidity and mortality after cardiac surgery. Prior work has identified several patient-related risk factors associated with HAIs. We hypothesized that rates of HAIs would differ across institutions, in part attributed to differences in case mix.

Methods and results: We analyzed 20 896 patients undergoing isolated coronary artery bypass grafting surgery at 33 medical centers in Michigan between January 1, 2009, and June 30, 2012. Overall HAIs included pneumonia, sepsis/septicemia, and surgical site infections, including deep sternal wound, thoracotomy, and harvest/cannulation site infections. We excluded patients presenting with endocarditis. Predicted rates of HAIs were estimated using multivariable logistic regression. Overall rate of HAI was 5.1% (1071 of 20 896; isolated pneumonia, 3.1% [n=644]; isolated sepsis/septicemia, 0.5% [n=99]; isolated deep sternal wound infection, 0.5% [n=96]; isolated harvest/cannulation site, 0.5% [n=97]; isolated thoracotomy, 0.02% [n=5]; multiple infections, 0.6% [n=130]). HAI subtypes differed across strata of center-level HAI rates. Although predicted risk of HAI differed in absolute terms by 2.8% across centers (3.9-6.7%; min:max), observed rates varied by 18.2% (0.9-19.1%).

Conclusions: There was a 18.2% difference in observed HAI rates across medical centers among patients undergoing isolated coronary artery bypass grafting surgery. This variability could not be explained by patient case mix. Future work should focus on the impact of other factors (eg, organizational and systems of clinical care) on risk of HAIs.

Keywords: cardiopulmonary bypass; infection; surgery.

Figure 1

Hospital-acquired infection subtype by strata of medical center. Centers are categorized as having low (<4.5%, n=14), medium (4.5–6.9%, n=15), or high (≥7.0%, n=4) infection rates. Rates of infection subtypes (pneumonia only, harvest site only, deep sternal wound only, sepsis or septicemia only, thoracotomy only, multiple infections) are reported across each strata of center.

Figure 2

Observed and predicted infection rates by medical center. Predicted rates were estimated based on year of procedure, age, body mass index, cerebrovascular disease, smoking, ejection fraction, dyslipidemia, hypertension, chronic lung disease, immunosuppressive therapy, peripheral arterial disease, diabetes mellitus, congestive heart failure, NY Heart Association Class, cardiogenic shock, and use of anticoagulants.