Septic Arthritis of the Knee Caused by Neisseria meningitidis Serogroup Y.

Authors

Takahiro Maruyama, Takahiro Yonemoto, Haruki Imura

Published in

Internal medicine (Tokyo, Japan). Oct 15, 2026. Epub Oct 15, 2026.

Abstract

Neisseria meningitidis is a notifiable pathogen in Japan when isolated from any sterile site. We describe a rare case of primary meningococcal arthritis without meningitis or bacteremia. A 48-year-old man presented with acute septic arthritis of his knee. A synovial fluid analysis using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed gram-negative diplococci, identified as N. meningitidis. Further antimicrobial susceptibility testing showed the isolate was pan-susceptible, allowing de-escalation from ceftriaxone to ampicillin therapy. The patient recovered fully after surgical drainage and 4 weeks of antibiotic therapy. This case highlights the importance of considering invasive meningococcal disease upon the detection of gram-negative diplococci in synovial fluid.

PMID:
42875200
Bibliographic data and abstract were imported from PubMed on 15 Oct 2026.

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