Haemophilus haemolyticus: an atypical pathogen of septic arthritis of the knee joint

Septic knee arthritis is a common disease, mostly due to bacterial infections. We describe a rare case of Haemophilus haemolyticus causing unilateral septic arthritis of a native knee. The affected patient presented with persistent severe knee pain after repeated intra-articular injections. Patient history included knee arthroscopy and a known rheumatoid arthritis treated by steroids. Since conservative treatment was ineffective and infection could not be excluded, diagnostic arthroscopy was performed. Synovial fluid and biopsies verified the uncommon microorganism and antibiotic therapy was initiated. Clinical findings and blood results showed rapid improvement. The patient was discharged in a good condition after 6 weeks. A review of the current literature describes only one joint infection with H. haemolyticus as underlying cause. In immunocompromised patients with septic knee arthritis also atypical pathogens must be considered. Nevertheless, the established treatment algorithm with arthroscopy and anti-infective therapy seems to be effective leading to satisfactory results.