[Pyogenic sacroiliitis: Lessons learned from an atypical case series]

Pyogenic sacroiliitis (PSI) is a rare condition that amounts to 1% to 2% of all joint infections in the paediatric age group. Its diagnosis is often difficult and delayed due to its nonspecific signs, symptoms and physical findings. Also, the identification of the causative microorganism is frequently challenging due to a high proportion of negative blood cultures and the risks involved in joint aspiration in this site.

We performed a retrospective review of the health records of all patients aged less than 18 years admitted to a tertiary children's hospital due to PSI between 2008 and 2016.

We identified 6 cases of paediatric PSI. The blood cultures were negative, and the identification of the causative agent required joint fluid aspiration in one patient with infection by Aggregatibacter aphrophilus, and specific screening tests for less frequent agents in the other patients: Kingella kingae (n=2), Brucella melitensis (n=1) and Bartonella henselae (n=1). The patients were treated with specific antimicrobial regimens, and all had favourable clinical outcomes and were free from sequelae during the follow-up.

Despite the small sample size, our study evinced the low effectiveness of blood cultures for diagnosis of paediatric PSI. It also highlights the need for a high level of suspicion for atypical agents and the early use of adequate diagnostic methods, including imaging and serological testing or polymerase chain-reaction (PCR) analysis of blood samples, as well as prescription of effective antimicrobial therapy.