# Seasonal viruses modify short-term air pollution effects on pediatric wheeze and asthma: a time-series study

## TL;DR

This study shows that seasonal viruses like rhinovirus can change how air pollution affects children's wheeze and asthma emergency visits.

## Contribution

The study demonstrates that viral activity modifies, rather than just confounds, the effects of air pollution on pediatric respiratory health.

## Key findings

- Exposure to NO₂ and PM2.5 was linked to increased WAD ED visits.
- High rhinovirus activity reduced the effect of air pollution on WAD ED visits.
- Ozone showed a negative association with WAD ED visits during low rhinovirus periods.

## Abstract

Short-term exposure to air pollution is a known trigger for pediatric wheeze-associated disorders (WAD), such as acute asthma and virus-induced wheezing, yet few air pollution studies account for concurrent viral circulation, which may confound or modify the observed associations. This study aims to assess whether viral circulation confounds or modifies the association between daily levels of air pollution and pediatric WAD emergency department (ED) visits.

We conducted a time-series analysis of 12,603 WAD ED visits among children 2–18 years old across eight hospitals in the Netherlands (2016–2023). Quasi-Poisson models estimated associations between same-day nitrogen dioxide (NO₂), fine and coarse particulate matter (PM₂․₅, PM₁₀) and ozone (O₃) and daily WAD ED visits, and adjusted for seasonality, meteorology and pollen. Base models were compared with confounding and interaction models, which included weekly rhinovirus (RV) or respiratory syncytial virus (RSV) positivity ratios as covariates or interaction terms.

In the base models, 3-day lag exposure to NO₂ and PM2.5 was associated with an increase in WAD ED visits (NO2: ER% 2.9, 95% CI 0.4—5.6; p = 0.025. PM2.5: ER% 3.6, 95% CI 0.4 – 6.9; p = 0.026). Associations were similar after adjustment for viral activity. The interaction models revealed attenuated effect estimates for NO2, PM2.5 and PM10 during relatively high RV activity. O₃ showed a negative association during low RV periods.

In this study, circulating RV modifies, rather than confounds, the association between short-term air pollution and pediatric WAD ED visits. Considering viral activity improves the interpretation of pollution–health associations and may explain inconsistencies across studies.

The online version contains supplementary material available at 10.1186/s12940-026-01274-y.