Gram-negative aetiology in hip and knee prosthetic joint infections: risk factors and implications for empirical antibiotic therapy-a retrospective cohort study.

Background: Empirical broad-spectrum antibiotic therapy is currently recommended for patients undergoing surgical treatment of prosthetic joint infections (PJIs), while awaiting intraoperative culture results. However, widespread use of Gram-negative coverage may lead to more adverse reactions, resistance selections and costs. Objectives: This study aimed to identify the factors associated with having a PJI caused by Gram-negative bacteria (GNB). Methods: This was an observational retrospective study of patients with hip and knee PJIs undergoing infection surgery between 2015 and 2019. PJI was defined according to 2018 Musculoskeletal Infection Society-International Consensus Meeting criteria. To assess risk factors for GNB-PJI, univariate and multivariate logistic regression analysis was carried out; statistical significance was considered for Results: A total of 281 patients were included, 137/281 (49%) were males, median age was 68 years (IQR 55-75), and the hip was involved in 147/281 (52%) cases. The most frequent surgical approach was a two-stage revision, carried out in 171/281 (61%), and the overall treatment failure rate was 19% (54/281). A Gram-negative aetiology was found in 51/281 (18%) cases; in this group the most frequent aetiological agents were Enterobacterales ( Conclusions: In our cohort, hip PJI was associated with a higher likelihood of GNB infection, whereas delayed-onset PJI was associated with a significantly lower likelihood.