Shifts in unidentified-pathogen acute hematogenous osteomyelitis incidence after non-pharmaceutical interventions highlight the role of seasonal viruses: an interrupted time-series analysis.

OBJECTIVE: To analyse the temporal association of COVID-19-related NPIs with the incidence of unidentified-pathogen acute hematogenous osteomyelitis (UP-AHO) in children aged 1-5 years, and to assess the contribution of seasonal viral circulation. METHODS: We conducted an interrupted time-series analysis from 2015 to 2023. Monthly UP-AHO incidence per 100,000 children was analysed using a quasi-Poisson regression model, considering seasonal viruses and their attributable fraction. RESULTS: Overall, 5 619 children were hospitalized for UP-AHO (median age: 2 years [IQR: 1-3]). The incidence of UP-AHO decreased following NPI implementation in March 2020 (immediate change, -57.6%; 95% CI, -72.2 to -42.5; p < 0.0001), then increased following school reopening in September 2020 (immediate change, 101.0%; 95% CI, 69.1 to 133.0; p < 0.0001). Population-level analyses showed that human rhinovirus accounted for 21.3% (95% CI, 5.8 to 36.8; p < 0.01) of the incidence of UP-AHO, and varicella-zoster virus for 9.8% (95% CI, 1.2 to 18.3; p = 0.03). Other viruses were not significantly associated. CONCLUSIONS: UP-AHO incidence was modified by NPIs and school reopening, reflecting shifts in seasonal viral circulation. Rhinovirus emerged as a driver of incidence shifts, in a context where Kingella kingae is a leading cause in children aged 1-5 years.