An 18-month-old female was brought to the emergency department because she presented with a 48-hour history of fever of 38.5o C maximum axillary temperature, limping, an antalgic attitude, pain and limitation to passive and active mobilisation of the left hip.
Blood tests were completed with elevated acute phase reactants (17,800 leukocytes with 53% neutrophils, 433,000 platelets, ESR 55 mm/hour, CRP 9.56 mg/dL and PCT 1.5 ng/mL), negative blood culture, bone x-ray without alterations and ultrasound of the hips with distension of the joint capsule and intra-articular echogenic content.
Given the suspicion of septic arthritis of the left hip, it was decided to perform an arthrocentesis in which purulent synovial fluid was obtained. A sample was sent for biochemistry and culture and empirical parenteral antibiotherapy was started with cefotaxime at 180 mg/kg and cloxacillin at 80 mg/kg. Synovial fluid results were compatible with septic arthritis and the joint fluid culture was positive for Haemophilus influenzae.
To determine a possible vaccine failure, given that the patient was correctly vaccinated for her age, a sample was sent to the reference hospital for typing of the bacteria, which turned out to be type f sensitive to cefotaxime. After a week in hospital, blood tests were performed with normal haemogram, white blood count and immunoglobulins.
In view of the results of the culture and antibiogram, intravenous cloxacillin was discontinued and the patient was given only parenteral cefotaxime at the same initial doses and the condition was monitored. After completing 10 days of intravenous antibiotherapy and 14 days of oral antibiotherapy (with amoxicillin-clavulanic acid), the evolution has been satisfactory (complete mobility, no pain, no limp when walking and no sequelae in imaging techniques performed after treatment was completed). The patient remains asymptomatic and without sequelae at 9 months of follow-up.

