Prosthetic joint infection caused by Neisseria sicca/subflava

Background Prosthetic joint infections are most commonly caused by staphylococci and streptococci, while commensal Neisseria species are exceedingly rare etiologic agents. Case presentation We report a 71-year-old white male with multiple comorbidities who presented with progressive left knee pain 9 years after total knee arthroplasty. Synovial fluid analysis showed an elevated leukocyte count with neutrophil predominance, and cultures subsequently grew Neisseria sicca / subflava . Given the concern for prosthetic joint infection, he underwent prosthesis explantation and received intravenous ceftriaxone 2 g daily for 6 weeks. Poor dentition was identified as a suspected potential source of hematogenous seeding. The patient demonstrated clinical improvement with surgical intervention and targeted antimicrobial therapy. Conclusion Neisseria sicca / subflava should be recognized as a rare but clinically significant cause of prosthetic joint infection.