Primary Septic Arthritis of the Hip Caused by Neisseria meningitidis Serogroup W135 in an Infant.

Septic arthritis in children is a medical and surgical emergency, most commonly caused by Staphylococcus aureus. Primary septic arthritis due to Neisseria meningitidis is extremely rare; the absence of meningeal signs often leads to significant diagnostic and therapeutic delay. We report a rare case of primary hip arthritis caused by Neisseria meningitidis serogroup W135 in an infant. A six-month-old infant with no significant medical history presented with fever and right hip pain following a flu-like syndrome. Clinical examination revealed a pseudoparalytic right limb and a fever of 39°C. Laboratory tests showed elevated inflammatory markers. While pelvic X-rays were normal, ultrasound confirmed a right hip joint effusion. Surgical arthrotomy was performed, yielding purulent fluid that identified Neisseria meningitidis serogroup W135. The patient received dual intravenous antibiotic therapy based on ceftriaxone and gentamicin, followed by oral cefixime. An immunodeficiency workup (HIV, immunoglobulins, and complement levels) was negative. After seven days, the patient showed significant clinical improvement and was discharged from the hospital. Monthly follow-up confirmed a full recovery. Although rare, Neisseria meningitidis should be considered a potential pathogen in pediatric septic arthritis. Early surgical drainage combined with appropriate antibiotic therapy ensures a favorable prognosis and prevents long-term joint sequelae.