Cutibacterium acnes in confirmed and probable deep shoulder infections

Introduction Cutibacterium acnes is frequently detected in tissue cultures of the shoulder, often in the absence of clear signs of infection. The aim of this retrospective study was to investigate the extent to which this bacterium appeared as the sole identifiable source of confirmed deep postoperative infections. Methods From a database containing all positive deep tissue cultures from the shoulder region at our department between 2015 and 2021. In total, 106 cases in which ≥2 positive cultures of the same bacterium were identified. Medical records were subsequently reviewed for evidence of a confirmed infection, defined as having ≥2 positive cultures of the same species alongside either a draining sinus or pus observed intraoperatively. Results C acnes was commonly detected in 63% of cases. Polymicrobial growth was identified in 21/106 cases. In confirmed infections, C acnes was the sole identifiable pathogen in 32% of cases. Beyond 3 months postoperatively both monomicrobial cases of C acnes and Staphylococcus aureus were identified in confirmed infections. Men were more likely to exhibit C acnes growth ( p  = 0.012). Conclusion C acnes is a clinically relevant pathogen, albeit slow growing, and is capable of independently causing significant deep surgical site infections.