A 66-year-old male presented with a 2-month history of right knee pain, swelling, and limited mobility, exacerbated by a fall one month prior. Initial synovial fluid analysis showed inflammatory markers, but routine cultures were negative. Subsequent 16S rRNA gene sequencing of the synovial fluid identified Neisseria mucosa, confirming a rare septic arthritis. The patient responded well to intravenous ceftriaxone followed by oral cefixime, showing significant improvement. This case highlights the importance of advanced molecular diagnostics, like 16S rRNA gene sequencing, for identifying unusual pathogens in culture-negative joint infections, preventing diagnostic delays and guiding appropriate treatment.
Key note: 16S rRNA gene sequencing is crucial for diagnosing septic arthritis caused by fastidious or unusual organisms like Neisseria mucosa when conventional cultures are negative.