Septic Arthritis of the Knee Caused by Neisseria meningitidis Serogroup Y

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.

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BibTeX RIS

BibTeX

@article{maruyama2026septic,
  title = {{Septic Arthritis of the Knee Caused by Neisseria meningitidis Serogroup Y}},
  author = {Takahiro Maruyama and Takahiro Yonemoto and Haruki Imura},
  journal = {Internal Medicine},
  year = {2026},
  month = oct,
  doi = {10.2169/internalmedicine.7610-26},
  url = {https://www.jstage.jst.go.jp/article/internalmedicine/advpub/0/advpub_7610-26/_article},
  note = {CC BY-NC-ND},
}

RIS

TY  - JOUR
TI  - Septic Arthritis of the Knee Caused by Neisseria meningitidis Serogroup Y
AU  - Takahiro Maruyama
AU  - Takahiro Yonemoto
AU  - Haruki Imura
PY  - 2026
DA  - 2026/10/15
JO  - Internal Medicine
DO  - 10.2169/internalmedicine.7610-26
UR  - https://www.jstage.jst.go.jp/article/internalmedicine/advpub/0/advpub_7610-26/_article
AB  - 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.
SN  - 1349-7235
SN  - 0918-2918
ER  -

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