Case Presentation: A 68-year-old male with osteoarthritis, status post bilateral knee replacement in 2014, presented with two weeks of flu-like symptoms, generalized weakness, and shortness of breath. Upon admission, the patient was noted to have a tender, swollen right knee with laboratories revealing neutrophilia with bandemia. Computed tomography (CT) of the joint revealed punctate gas further concerning for septic arthritis, and he was transferred for our facility for additional workup. Blood and sputum cultures drawn prior to empiric antibiotics grew beta-lactamase negative non-typeable Haemophilus influenzae. Synovial fluid analysis from the right knee, drawn after empiric antibiotics, was sterile but turbid with a neutrophil count of 213,000. His primary source of infection was presumed to have been respiratory, which secondarily seeded the right knee prosthesis hematogenously. During his admission, he also developed a tender, fluctuant mass at his right sterno-clavicular joint with thickening of the overlying sternocleidomastoid and pectoralis major muscles, concerning for an additional focus of infection. Antibiotic therapy was narrowed to ceftriaxone monotherapy. From a surgical standpoint, he underwent exploration of his right sternoclavicular joint in addition to incision and drainage of the right knee with debridement, antibiotics, and implant retention (DAIR).

Discussion: Polyarticular septic arthritis is rarely caused by Haemophilus influenzae. Most cases have been reported in immunocompromised patients, with risk factors including HIV and multiple myeloma, though one polyarticular case has been described in an otherwise healthy young adult and another in an otherwise healthy infant. [1-4] Infection of a joint with Haemophilus influenzae has been noted to be the presenting symptom leading to the discovery of an immunocompromised state. [5] Following the standard of care for management of septic arthritis, patients responded well to long-term antibiotic therapy and surgical debridement. Our case presentation is novel in that it describes a polyarticular joint infection involving both native and prosthetic joints in a patient without known immunocompromise. This case also highlights the importance of high clinical suspicion for septic arthritis in patients presenting with a non-musculoskeletal chief complaint.

Conclusions: Haemophilus influenzae is an uncommon causative pathogen of polyarticular septic arthritis in the adult immunocompetent patient population. Infection can involve multiple systems and collaboration across specialties is crucial for optimizing management and preventing permanent sequelae.