Periprosthetic joint infection (PJI) is a serious complication after joint arthroplasty, with polymicrobial PJIs representing a distinct subset associated with worse outcomes. This study aims to characterize the risk factors, microbiological profiles, and clinical outcomes of polymicrobial PJIs in a single tertiary care center. A retrospective analysis was conducted on 499 patients diagnosed with PJI between 2010 and 2023. Polymicrobial infection was defined by isolation of ≥2 distinct pathogens from intraoperative samples. Demographic, microbiological, and clinical data were analyzed. Treatment success was defined as infection eradication without recurrence or chronic suppressive therapy. Polymicrobial PJIs accounted for 18.2% of cases. Patients with polymicrobial infections had higher rates of obesity, insulin-dependent diabetes, and higher Charlson comorbidity scores. Coagulase-negative staphylococci and gram-negative bacilli were more frequently isolated in polymicrobial infections, while S. aureus predominated in monomicrobial cases. Treatment success rates were significantly lower in polymicrobial infections, both in acute (61.5% vs. 94.5%, p = 0.003) and chronic settings (51.3% vs. 75.3%, p = 0.02). Polymicrobial PJIs are associated with distinct microbiological patterns, increased comorbidity burden, and significantly worse clinical outcomes. Recognition of specific risk factors and pathogen profiles is essential to optimize management strategies for this complex condition.

Introduction: Androgen deprivation therapy remains the essential treatment for disseminated prostate cancer. Interstitial pneumonitis following this therapy has been documented for just a few cases. However, reported cases frequently describe the onset of symptoms after recent administration (days or a few weeks) of both GnRH analogues and androgen antagonists, which makes the precise individual impact of each treatment difficult to estimate. Case report: This report presents a case of a 94-year-old patient with interstitial pneumonitis whose onset started three months after the first dose of leuprorelin and bicalutamide for a metastatic prostate cancer. Management and outcome: Once other possible diagnosis were ruled out, empiric corticosteroid treatment was initiated within 48 h of the admission. A spectacular clinical and radiological improvement was observed after 3 doses of steroids, enabling the patient to recover his basal respiratory situation. We considered that the most probable cause was toxic interstitial pneumonitis induced by leuprorelin. Discussion: To our knowledge, it describes the longest interval between last administration of antiandrogen therapy and the development of pneumonitis. This fact may support a direct relation with leuprorelin, whose serum levels remain high for months because of its long-acting depot formulation.