Sternal wound infection after cardiac surgery: incidence and risk factors according to clinical presentation

The incidence of surgical site infection (SSI) after cardiac surgery depends on the definition used. A distinction is generally made between mediastinitis, as defined by the US Centers for Disease Control and Prevention (CDC), and superficial SSI. Our objective was to decipher these entities in terms of presentation and risk factors. We performed a 7-year single centre analysis of prospective surveillance of patients with cardiac surgery via median sternotomy. SSI was defined as the need for reoperation due to infection. Among 7170 patients, 292 (4.1%) developed SSI, including 145 CDC-defined mediastinitis (CDC-positive SSI, 2.0%) and 147 superficial SSI without associated bloodstream infection (CDC-negative SSI, 2.1%). Median time to reoperation for CDC-negative SSI was 18 days (interquartile range, 14-26) and 16 (interquartile range, 11-24) for CDC-positive SSI (p 0.02). Microorganisms associated with CDC-negative SSI were mainly skin commensals (62/147, 41%) or originated in the digestive tract (62/147, 42%); only six were due to Staphylococcus aureus (4%), while CDC-positive SSI were mostly due to S. aureus (52/145, 36%) and germs from the digestive tract (52/145, 36%). Risk factors for SSI were older age, obesity, chronic obstructive bronchopneumonia, diabetes mellitus, critical preoperative state, postoperative vasopressive support, transfusion or prolonged ventilation and coronary artery bypass grafting, especially if using both internal thoracic arteries in female patients. The number of internal thoracic arteries used and factors affecting wound healing were primarily associated with CDC-negative SSI, whereas comorbidities and perioperative complications were mainly associated with CDC-positive SSI. These 2 entities differed in time to revision surgery, bacteriology and risk factors, suggesting a differing pathophysiology.