Bidirectional changes in recorded pediatric asthma diagnoses with respiratory virus activity: A nationwide interrupted time-series analysis in Japan.

BACKGROUND: Early-life respiratory infections are associated with subsequent asthma development; however, whether respiratory viruses contribute to asthma onset or merely unmask pre-existing susceptibility remains unclear. The COVID-19 pandemic's non-pharmaceutical interventions (NPIs) suppressed respiratory viruses, followed by their resurgence, offering a natural experiment. We examined whether these population-level changes in respiratory virus activity were associated with changes in newly recorded pediatric asthma diagnoses. METHODS: We conducted a nationwide interrupted time-series study using Japan's National Database of Health Insurance Claims, covering approximately 99% of the population. Segmented negative binomial regression with two intervention points-NPI implementation (T1: March 2020) and COVID-19 reclassification (T2: May 2023)-was applied to monthly counts of newly recorded asthma diagnoses among children aged under 19 years (January 2018-March 2024), with atopic dermatitis as negative control. Age-stratified/sex-stratified analyses and exploratory ecological analyses of pathogen-specific associations were conducted. RESULTS: Among 10,508,387 new asthma diagnoses, incidence declined significantly following NPI implementation (incidence rate ratio [IRR] 0.511, 95% confidence interval [CI] 0.422-0.620) and rebounded following NPI relaxation (IRR 1.395, 95% CI:1.120-1.737). Atopic dermatitis showed attenuated changes at both points. Rate differences were greatest in infants (0-1 years) at T1 and school-aged children (5-9 years) at T2. Rhinovirus, respiratory syncytial virus, influenza, and Mycoplasma pneumoniae, but not SARS-CoV-2, correlated with asthma diagnoses in ecological analyses. CONCLUSIONS: Newly recorded pediatric asthma diagnoses showed bidirectional changes that paralleled respiratory virus suppression and resurgence, compatible with a possible contributory role of respiratory infections, particularly among infants and school-aged children.