<i>Proteus</i>-species-associated periprosthetic hip and knee joint infections – a 15-year cohort analysis

<b>Introduction</b>: While Gram-negative periprosthetic joint infections (PJIs) are generally known for their poor outcome, few data on <i>Proteus</i> species exist. Therefore, we investigated the prevalence, clinical characteristics, microbial spectrum, outcomes, antimicrobial treatment, and surgical procedures of <i>Proteus</i>-species-associated PJIs. <b>Methods</b>: We retrospectively evaluated 1776 culture-positive revision hip and knee arthroplasties (hereafter rTHA and rTKA, respectively) from a single institution between 2008 and 2024. The European Bone and Joint Infection Society and International Consensus Meeting criteria were used for classification. The Charlson comorbidity score and tier classification were used for evaluating risk factors and success and failure rates. Statistical analysis was performed using the chi-square test and binary logistic regression. <b>Results</b>: Among 1776 culture-positive revision arthroplasties, we identified 26 (1.5 %) <i>Proteus</i>-species-associated PJIs. The majority were observed in rTHA, mostly in chronic (65.4 %) and polymicrobial (57.7 %) infections. Chronic PJIs were associated with polymicrobial infections ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.027</mml:mn></mml:mrow> </mml:math> ), resulting in a higher failure rate ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.041</mml:mn></mml:mrow> </mml:math> ). Among polymicrobial infections (15 of 26 cases), <i>Enterococcus faecalis</i> (5 of 15), <i>Staphylococcus epidermidis</i> (4 of 15), and <i>Pseudomonas aeruginosa</i> (3 of 15) were most frequently observed. The most frequently used surgical approach was a two-stage revision (46.2 %), with a success rate of 25 % (3 of 12). <i>Proteus</i>-species-associated PJIs were mainly treated with fluoroquinolone, especially ciprofloxacin showed higher success rates ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.018</mml:mn></mml:mrow> </mml:math> ). The reinfection-free survival rate was 48.5 % after 12 months and 22.6 % after 40 months. <b>Conclusion</b>: <i>Proteus</i> species represent a rare group of pathogens and are predominantly found in chronic and polymicrobial PJIs, with a higher occurrence in rTHA than rTKA. Despite an overall high clinical failure rate, ciprofloxacin showed promising antimicrobial treatment efficacy.