Extreme weather and paediatric asthma hospitalisations: a 20-year study in tropical and subtropical coastal cities

The impact of extreme temperature events on paediatric asthma hospitalisations remains understudied in coastal cities with different thermal environments. Using long-term weekly asthma hospitalisation data from Cairns (tropical) and Brisbane (subtropical), Queensland, Australia (2000–2019), we applied multilevel negative binomial regression models with random intercepts for Statistical Area Level 2 (SA2) regions to examine associations between Universal Thermal Climate Index (UTCI)-defined cold spells and heat waves and asthma hospitalisation rates among children and adolescents aged 5–19 years. Models were adjusted separately for SO₂, NO₂ and PM₂.₅, with stratified analyses by age, sex, socioeconomic status and land-cover characteristics. Cold spells and heat waves occurred during approximately 6%-10% of weekly observations across SA2 areas within their respective seasons. In the SO₂-adjusted models, cold-spell estimates were positive in Cairns (relative risk (RR) 1.18, 95% CI 0.99–1.41) and Brisbane (RR 1.11, 95% CI 1.03–1.19), with similar directions but varying precision across pollutant-adjustment models. Heat-wave estimates were inverse in Brisbane (RR 0.84, 95% CI 0.78–0.90) but imprecise in Cairns (RR 0.82, 95% CI 0.65–1.04), with attenuation in some alternative pollutant-adjustment models. Formal interaction tests supported age-related effect modification in Brisbane for cold spells ( p = 0.007) and heat waves ( p = 0.045), while other subgroup interactions were not statistically significant. Between-city heterogeneity tests did not provide statistical evidence that city-specific estimates differed. Sensitivity analyses using alternative percentile thresholds and consecutive-day criteria showed greater variability in some estimates, particularly for cold spells in Cairns. Distributed lag models showed positive cold-spell estimates at lag 0 and inverse heat-wave estimates over short lags, with patterns varying by city and pollutant model. These findings suggest that UTCI-defined extreme temperature events are associated with paediatric asthma hospitalisations in coastal Queensland.