In-hospital surgical site infections after primary hip and knee arthroplasty--incidence and risk factors.

Data of hospitalizations for THA or TKA were analyzed for each year between 1998 and 2007 from the National Inpatient Sample. Demographics, comorbidities, incidence of morbidity and mortality, length of hospital stay (LOS), and overall cost were compared for infected and non-infected patients. Perioperative SSI rates were 0.36% for THA and 0.31% for TKA (412,356 and 784,335 patient entries, respectively). Patients with SSI had a significantly higher overall comorbidity burden, higher perioperative mortality rates, longer length of stay, and higher complication rates. Average cost of in-hospital care was double for SSI versus non-SSI patients. Independent risk factors for perioperative SSI included male gender, minority race, a diagnosis for cancer, liver disease, coagulopathies, fluid and electrolyte disorders, congestive heart failure, and pulmonary circulatory disease. Data relied on coded information and could not differentiate between superficial or deep infection, or capture patients readmitted for SSI, and therefore may have underestimated the true incidence of SSI.