The increased demand for hip arthroplasty means a growing number of postsurgical complications. This study aims to assess the risk of surgical site infection (SSI) in a teaching hospital; develop regional, national and international external comparisons; and evaluate SSI-related risk factors, particularly according to the timing of surgery (urgent/unplanned or elective).

Prospective cohort study from January 2008 to December 2018. Patients were followed up to 90 days after surgery. Primary endpoint was SSI incidence according to the Centers for Disease Control and Prevention criteria. Multivariate analysis was conducted to find independently associated SSI risk factors. The association between risk factors and SSI incidence was assessed by reference to odds ratio (OR). Analyses were also performed among urgent/unplanned and elective patients to identify whether SSI risk factors differed between groups.

The study population (n = 1,808) has an overall SSI rate of 3.0% (95% confidence interval [CI]: 2.4-3.9). Timing of surgery caused an effect modification, so surgery duration> 75th percentile (OR: 3.8; 95% CI: 1.5-9.8) and inadequate preparation (OR: 3.3; 95% CI: 1.1-10.0) were independent risk factors in the urgent/unplanned group; National Healthcare Safety Network risk index≥ 2 (OR: 6.3; 95% CI: 0.1-19.2) and transfusion (OR: 3.6; 95% CI: 1.1-11.9) in the elective group.

Hospital infection surveillance systems allow identifying risk factors susceptible to change. Characterization of factors that caused an effect modification is key to identify areas of quality improvement, including reducing operating times, preventing perioperative blood transfusion, or improving patient preparation before surgery.