[Primary meningococcal septic arthritis in a two month old infant].

Meningococcal septic arthritis, ocurring without signs of sepsis, is rare, including at pediatric age. The confinement of infection to a single articulation (monoarticular form) is even rarer in infections by Neisseria spp. We discuss the case of a two month-old caucasian girl, presenting with fever and persistent crying during nappy change. Absence of clinical sepsis was notable. She had had no previous anti-meningococcal immunizations. The ultrasound of the left hip revealed the presence of intra-articular fluid. Culture of the purulent sample after drainage by arthrotomy produced Neisseria meningitidis. She had a good clinical response to the antibiotics. Follow-up showed no sequels. Albeit a rare entity, primary meningococcal arthritis is a mandatory differential diagnosis concerning a feverish child with articular complaints.