A Canadian surveillance study of 2831 hospitalized children with confirmed COVID-19 examined whether coinfection with other respiratory viruses increased severity. Among 938 children at centres with systematic multiplex PCR testing of all acute respiratory admissions, 18.6% had ≥1 coinfection (RSV 39.7%, enterovirus/rhinovirus 38.5% most common). Coinfections showed no increased odds of severe COVID-19 (aOR 0.94, 95% CI 0.76–1.15), but appeared associated with severity in secondary analyses without systematic testing (aOR 1.42), suggesting prior estimates of coinfection severity were confounded by differential testing practices.
Why it is interesting: Demonstrates that prior observational findings of worse outcomes with coinfection may have reflected ascertainment bias rather than true biological interaction, a methodological lesson for respiratory virus surveillance.