How Should Bacteriological Sampling Be Stratified in Paediatric Septic Arthritis? A Narrative Review with a Proposed...

Joint aspiration remains the gold standard and an urgent step in the diagnosis of paediatric septic arthritis (SA). Unlike in acute haematogenous osteomyelitis, it has both diagnostic and therapeutic value. No previous review has specifically addressed when bacteriological sampling is essential and when it may reasonably be omitted. The bacteriological profile in children is highly age-dependent: Kingella kingae predominates before 4 years of age, whereas Staphylococcus aureus-including Panton-Valentine leukocidin (PVL)-producing and methicillin-resistant (MRSA) strains-predominates thereafter. We critically review the evidence through nine clinical questions and propose a conceptual risk-stratified framework in which the sampling approach is tailored to age and clinical context. In children younger than 4 years with a positive oropharyngeal K. kingae PCR and a mild clinical presentation-defined as CRP < 20 mg/L, absence of fever, and preserved weight-bearing-non-invasive confirmation may be sufficient. This proposal is explicitly hypothesis-generating: it is derived from observational data, it has not been validated prospectively, and it is not endorsed by current PIDS/IDSA or ESPID guidance. A positive oropharyngeal PCR alone is never sufficient, given the 10-12% asymptomatic carriage rate and the limited reliability of the Kocher-Caird criteria in this age group; the decision requires a cluster of concordant findings together with mandatory clinical and laboratory reassessment at 48-72 h and a low threshold for escalation to arthrocentesis. In children older than 4 years, arthrocentesis under general anaesthesia remains the standard approach, with pathogen identification and antimicrobial susceptibility testing as the primary microbiological determinants of therapy and toxin profiling as an adjunctive investigation in selected cases.