Some patient populations and types of orthopaedic surgery could be at particular risk for anaerobic infections. In this retrospective cohort study of operated adult patients with infections from 2004 to 2014, we assessed obligate anaerobes and considered first clinical infection episodes. Anaerobes, isolated from intra-operative samples, were identified in 2.4% of 2740 surgical procedures, of which half (33/65; 51%) were anaerobic monomicrobial infections. Propionibacterium acnes, a penicillin and vancomycin susceptible pathogen, was the predominantly isolated anaerobe. By multivariate analysis, the presence of fracture fixation plates was the variable most strongly associated with anaerobic infection (odds ratio: 2.1, 95% CI: 1.3-3.5). Anaerobes were also associated with spondylodesis and polymicrobial infections. In contrast, it revealed less likely in native bone or prosthetic joint infections and was not related to prior antibiotic use. In conclusion, obligate anaerobes in our case series of orthopaedic infections were rare, and mostly encountered in infections related to trauma with open-fracture fixation devices rather than clean surgical site infection. Anaerobes were often co-pathogens, and cultures most frequently recovered P. acnes. These observations thus do not support changes in current practices such as broader anaerobe coverage for perioperative prophylaxis.
Keywords: Orthopaedic infections; anaerobes; antibiotic prophylaxis; epidemiology.