A Comparison of Causative Pathogens in Bone and Prosthetic Joint Infections: Implications for Antimicrobial Therapy

<b>Background</b>: The microbiological profile of bone and joint infections is important for determining the empiric choice of both systemic and local antimicrobial therapy. This study assessed whether there was a difference in the bacterial species that were isolated on culture in osteomyelitis (OM), fracture-related infection (FRI) or prosthetic joint infection (PJI). This was a retrospective, observational cohort study of patients who had surgical intervention for PJI or OM or FRI with a positive microbial culture between 2019 and 2022. <b>Methods</b>: Data including patient demographics, the site of injury, JS-BACH score, organism classification and antibiotic resistance to vancomycin and gentamicin were extracted from the medical records. <b>Results</b>: A total of 440 patients were included in this study: 163 patients with osteomyelitis, 109 with fracture-related infection with fixation implants and 168 with prosthetic joint infection. The patients with PJI were older, more likely to be female and had a higher BMI and ASA score compared to those with OM. Patients with PJI were more likely to have a higher JS-BACH score and more complex infections. <i>Staphylococcus aureus</i> was the most commonly isolated organism in all three groups. It was more frequently isolated in osteomyelitis than in PJI (<i>p</i> = 0.016). In both osteomyelitis and FRI, after <i>Staphylococcus aureus,</i> the next most common organisms were Gram-negatives, whilst for PJIs, the most commonly isolated organisms were <i>Staphylococcus aureus</i>, followed by coagulase-negative <i>Staphylococci</i> and then <i>Streptococcus</i> species. The rates of other organisms were broadly similar between the three groups. When adjusted for confounders, including symptom duration, JS-BACH score, the location of injury, age and BMI, there was no statistically significant difference in the presence of <i>Staphylococcus aureus</i> (OR = 0.765; 95% CI 0.633-1.232; <i>p</i> = 0.465) or polymicrobial infection (OR = 1.175; 95% CI 0.803-1.721; <i>p</i> = 0.407). <b>Conclusions</b>: Causative pathogens are similar across bone and joint infections and are independent of the presence of prosthetic material.