Background: Transient synovitis of the hip affects mostly preschool children, and its etiology is unknown. Kingella kingae has been identified recently as a common etiologic agent of osteoarticular infections (OAI) in young children and could potentially be associated to transient synovitis of the hip. The main objective of this study was to evaluate the association between transient synovitis of the hip and oropharyngeal carriage of K. kingae among preschool children.

Methods: This was a prospective case-control study conducted at a tertiary care pediatric emergency department. Cases were children between 6 and 71 months of ages with a diagnosis of transient synovitis of the hip. For each transient synovitis case, an age-matched control was recruited among children presenting for a trauma. A second control group included children with any OAI. The independent variable was the presence of oropharyngeal K. kingae identified by a specific polymerase chain reaction assay. The primary analysis was the association between oropharyngeal K. kingae carriage and final diagnosis.

Results: A total of 73 children were included in the study. Among them, 25 had a transient synovitis, 16 an OAI, and 22 controls. Baseline demographics were similar between the groups. There was no difference in oropharyngeal carriage of K. kingae for children with transient synovitis (5/25; 0.20) in comparison to controls (3/22; 0.14), while it was higher for children with OAI (10/16; 0.63).

Conclusions: There is no association between oropharyngeal K. kingae and transient synovitis of the hip among preschool children.