Abstract Introduction Haemophilus influenzae type b (H. influenza, Hib) is an uncommon cause of septic arthritis in adults and a rare etiology of prosthetic joint infection (PJI). Before the widespread introduction of the Hib vaccine, arthritis accounted for approximately 2 % of invasive Hib infections in children. In the post-vaccination era, invasive Hib disease in adults has become exceedingly rare, with an estimated incidence of 0.03 per 100,000 among adults aged ≥65 years in the United States. Despite its rarity, Hib infection can cause severe systemic illness in individuals with underlying comorbidities or uncertain immunization status. Case Presentation A 65-year-old woman with hypertension, diabetes mellitus, obesity post-gastric bypass (2003), gastroesophageal reflux disease, peripheral vascular disease, and bilateral total knee arthroplasties (placed 19 years earlier) presented with acute confusion and altered mental status. History revealed trauma from a bicycle injury within two weeks prior to admission. Examination showed fever (100.8 °F), tachycardia of 125 beats per minute, disorientation, and diffuse swelling, warmth, and tenderness of the left knee with restricted range of motion. Laboratory studies demonstrated leukocytosis (16,400/µL, neutrophil predominant), erythrocyte sedimentation rate of 105 millimeter/hour, c-reactive protein of 80 mg/L, and Creatinine kinase of 1117 U/L. Imaging showed mild suprapatellar effusion without fracture, and Doppler ultrasound ruled out deep vein thrombosis. Empiric ceftriaxone and vancomycin were initiated under sepsis protocol. Arthrocentesis revealed purulent synovial fluid with 92,000 leukocytes (87% neutrophils). The patient underwent explantation of prosthetic components, extensive debridement, synovectomy, irrigation, and placement of an antibiotic-impregnated spacer. Blood and synovial fluid cultures grew H. influenzae type b sensitive to ampicillin, confirming the diagnosis. Antibiotics were narrowed to intravenous ceftriaxone for four weeks followed by two weeks of oral therapy. Pathology demonstrated acute and chronic necrotizing inflammation with abscess formation, consistent with infection. Discussion and Conclusion This case highlights an exceptionally rare presentation of Hib-associated prosthetic knee infection with sepsis and encephalopathy in an elderly adult. Given the rarity of the condition, awareness remains essential for early recognition and management. Prompt surgical intervention combined with pathogen-directed antibiotic therapy led to complete clinical recovery. Clinicians should consider Hib in atypical PJI presentations, especially in patients with uncertain vaccination history or immunocompromising conditions. This abstract is funded by: None
Gharti et al. (Fri,) studied this question.