O11 Neisseria Meningitidis as a cause of isolated bilateral polyarticular native knee joint septic arthritis

Abstract Case report - Introduction Septic Arthritis is a medical emergency with a significant mortality and morbidity. The aim of management is to minimise the risk of irreversible joint damage and to preserve function. We present the case of a 63-year-old lady admitted with bilateral knee pain and swelling, lower limb rash and a fever who was initially managed as a reactive arthritis but subsequent Polymerase Chain Reaction (PCR) molecular analysis revealed capsular group B N. meningitidis in bilateral knee aspirates. We discuss the diagnostic challenges in differentiating septic arthritis from inflammatory arthritis, and the role of PCR molecular analysis in that process. Case report - Case description A 63-year-old female presented with a 5-day history of painful, stiff and swollen knees bilaterally with decreased range of movement. Five days prior to presentation she suffered from a sore throat, fever and lower limb rash for which she was started on flucloxacillin with some improvement. Co-morbidities included hyperlipidaemia and a hysterectomy. Regular medication included naproxen. On examination her temperature was 37.7C and she was haemodynamically stable. Both knees demonstrated active synovitis. Admission bloods were remarkable for a CRP of 399 and deranged liver function tests. Knee X-rays revealed a moderate effusion in the left knee, and a large effusion in the right. The patient was given a dose of intravenous Co-amoxiclav with a working diagnosis of septic arthritis. Aspiration of both knees was performed with 120 mls of yellow-coloured fluid aspirated from the left knee and 90 mls from the right knee. No organisms were identified on Gram Stain and no growth at 48 hours on culture. Synovial fluid from both knees was sent for broad-based bacterial 16S rDNA PCR molecular testing. The patient was reviewed 4-weeks later at which stage her symptoms had improved. Prednisolone had been stopped a week prior with no deterioration in her joint symptoms. Peripheral blood cultures taken during admission revealed no growth at 5 days. After discharge the results of the molecular PCR testing on the synovial fluid samples became available and were positive for bacterial 16S rDNA. Referral to the Public Health England Meningococcal Reference Unit ensued and further molecular typing confirmed N. meningitidis with capsular genogroup B. Subsequent non-culture sequencing of the factor H binding protein and PorA epitope revealed it to belong to the subtype P 1.12