Pediatric Clinical Influenza Disease by Type and Subtype 2015-2020: A Multicenter, Prospective Study.

Background: Previous investigations into clinical signs and symptoms associated with influenza types and subtypes have not definitively established differences in the clinical presentation or severity of influenza disease.

Methods: The study population included children 0-17 years old enrolled at 8 New Vaccine Surveillance Network sites between 2015 and 2020 who tested positive for influenza virus by molecular testing. Demographic and clinical data were collected for study participants via parent/guardian interviews and medical chart reviews. Descriptive statistics were used to summarize demographic and clinical characteristics by influenza subtype. Multivariable logistic regression and Cox proportional hazard models were used to assess the effects of age, sex, influenza subtype, and history of asthma on severity, including hospital admission, need for supplemental oxygen, and length of stay.

Results: Retractions, cyanosis, and the need for supplemental oxygen were more frequently observed among patients with influenza A(H1N1)pdm09. Headaches and sore throat were more commonly reported among patients with influenza B. Children with influenza A(H1N1)pdm09 and children with asthma had significantly increased odds of hospital admission (adjusted odds ratio [AOR]: 1.39, 95% confidence interval [CI]: 1.14-1.69; AOR: 2.14, 95% CI: 1.72-2.67, respectively). During admission, children with influenza A(H1N1)pdm09 had significantly increased use of supplemental oxygen compared to children with A(H3N2) (AOR: 0.60, 95% CI: 0.44-0.82) or B (AOR: 0.56, 95% CI: 0.41-0.76).

Conclusions: Among children presenting to the emergency department and admitted to the hospital, influenza A(H1N1)pdm09 caused more severe disease compared to influenza A(H3N2) and influenza B. Asthma also contributed to severe influenza disease regardless of subtype.