Haemophilus parainfluenzae as a Causative Organism in Periprosthetic Joint Infection: A Case Report.

BACKGROUND: Haemophilus parainfluenzae (H. parainfluenzae) is rare in periprosthetic joint infections (PJIs). While many cases are associated with a prior history suggestive of an oral source, many occur without an identifiable source or exposure. We review two patients who had concerns for PJI, later identified as H. parainfluenzae through intraoperative cultures. CASE REPORT: Two patients presented with complaints of knee pain. The first, a 54-year-old male, was found on admission to have a knee PJI. The patient underwent debridement, antibiotics, and implant retention (DAIR) and was discharged on intravenous (IV) ceftriaxone after H. parainfluenzae was isolated on culture, with no resistance reported on susceptibilities. However, approximately 4 weeks later, the patient underwent a second DAIR due to persistent swelling and redness; cultures were negative at the time of the second surgery. He was treated with IV vancomycin and cefepime and placed on cefadroxil suppression therapy without additional surgery. The second patient, an 80-year-old male, had a history of prior knee PJI, methicillin-resistant staphylococcus aureus (MRSA) in 2009 and Streptococcus agalactiae in 2015. He presented with a draining sinus and pain over his knee. Resection arthroplasty and above knee amputation were offered, but he would only consent to DAIR; intraoperative cultures showed H. parainfluenzae. He was treated with IV ceftriaxone postoperatively and then oral suppression. CONCLUSIONS: Due to increasing resistance in this species worldwide, consideration should be taken when choosing antimicrobial therapy for H. parainfluenzae. From the limited data available, patients with PJI secondary to H. parainfluenzae have a better prognosis compared to PJI with other Gram-negative organisms.