Sources of Variation in Hospital-Level Infection Rates After Coronary Artery Bypass Grafting: An Analysis of The Society of Thoracic Surgeons Adult Heart Surgery Database

Abstract

Background: Patients undergoing coronary artery bypass grafting (CABG) are at risk for a variety of infections. Investigators have focused on predictors of these adverse sequelae, but less attention has been focused on characterizing hospital-level variability in these outcomes.

Methods: Between July 2011 and December 2013, The Society of Thoracic Surgeons Adult Cardiac Surgery Database shows 365,686 patients underwent isolated CABG in 1,084 hospitals. Hospital-acquired infections (HAIs) were defined as pneumonia, sepsis/septicemia, deep sternal wound infection/mediastinitis, vein harvest/cannulation site infection, or thoracotomy infection. Hospitals were ranked by their HAI rate as low (≤ 10th percentile), medium (10th to 90th percentile), and high (>90th percentile). Differences in perioperative factors and composite morbidity and mortality end points across these groups were determined using the Wilcoxon rank sum and χ(2) tests.

Results: HAIs occurred among 3.97% of patients overall, but rates varied across hospital groups (low: <0.84%, medium: 0.84% to 8.41%, high: >8.41%). Pneumonia (2.98%) was the most common HAI, followed by sepsis/septicemia (0.84%). Patients at high-rate hospitals more often smoked, had diabetes, chronic lung disease, New York Heart Association Functional Classification III to IV, and received blood products (p < 0.001); however, they less often were prescribed the appropriate antibiotics (p < 0.001). Major morbidity and mortality occurred among 12.3% of patients, although this varied by hospital group (low: 8.6%, medium: 12.3%, high: 17.9%; p < 0.001).

Conclusions: Substantial hospital-level variation exists in postoperative HAIs among patients undergoing CABG, driven predominantly by pneumonia. Given the relatively small absolute differences in comorbidities across hospital groups, our findings suggest factors other than case mix may explain the observed variation in HAI rates.

Figure 1

Overall Rate of Hospital-Acquired Infections Among 1084 Participating Hospitals. Hospital-acquired infections (HAIs) were defined as: pneumonia, sepsis/septicemia, deep sternal wound infection/mediastinitis, vein harvest/cannulation, or thoracotomy

Figure 2

Risk of Composite Endpoint by Strata of Hospital-Acquired Infections Among 1084 Participating Hospitals. Morbidity/Mortality defined as any of the following: operative mortality, reoperation for cardiac reasons, renal failure (in patients without preoperative dialysis or preoperative creatinine >4mg/dl) or prolonged ventilation.