Beyond Gram-Negative and Gram-Positive Bacteria: Virulence as a Determinant of Clinical Outcome in Periprosthetic Joint Infections.

Abstract

Gram-negative (GN) periprosthetic joint infections (PJIs) are still less frequent than Gram-positive (GP) PJIs. There is only little data available on a direct comparison of GP- and GN-associated PJIs. Therefore, we investigated the outcome of GN and GP hip and knee PJI according to the virulence of the pathogens in a matched cohort. We retrospectively evaluated 1,695 culture-positive revision hip and knee arthroplasties from a single institution performed between 2008 and 2024. Infection-confirmed PJIs, according to the European Bone and Joint Infection Society criteria, were included. Polymicrobial cases with mixed GN and GP pathogens and anaerobic infections were excluded. A 1:3 propensity score matching for Charlson Comorbidity Score (CCI), age, sex, hip, and knee was performed using logistic regressions. The GP PJIs were divided into low (150 of 252; 59.5%) and high-virulent pathogens (102 of 252; 40.5%). Outcomes were determined using the Tier classification by the Musculoskeletal Infection Society. The GN PJIs demonstrated a significantly worse outcome than GP PJIs (P = 0.032) and a 1.64-fold higher risk of reinfection. High-virulent GN/GP PJIs have shown a significantly worse outcome than low-virulent PJIs. There was no statistical significance identified when comparing high-virulent GP PJIs and GN PJIs (P = 0.73). In GN PJIs, single-stage procedures showed the highest success rate (62.5%), whereas debridement, antibiotics, and implant retention showed the lowest (30.8%). Resistance to fluoroquinolones was observed in up to 24% of GN pathogens. However, treatment with fluoroquinolones did not result in a higher success rate (P = 0.214). To our knowledge, this is the first study comparing GN PJIs and GP PJIs based on their virulence, demonstrating that GN PJIs have a significantly worse outcome than GP PJIs. However, high-virulent GP PJIs have shown the same outcome as GN PJIs, suggesting that virulence plays an equally important role in determining the outcome of PJIs.