Extreme Cold Events and Pediatric Asthma Outpatient Visits: The Modifying Role of Ambient Carbon Monoxide and Sulfur...

Extreme cold exposure may trigger respiratory morbidity in children, but whether concurrent ambient air pollution modifies cold-related risks of pediatric asthma remains unclear. This study evaluated associations between extreme cold events and pediatric asthma outpatient visits and assessed whether these associations differed according to ambient pollutant concentrations.

We conducted a time-series study of 62,167 pediatric asthma outpatient visits among children diagnosed with asthma at a tertiary children's hospital in Nanjing, China, from 2019 to 2024. Daily asthma visits were linked with meteorological variables and ambient concentrations of PM₁₀, PM_2.5, NO₂, SO₂, CO, and O₃. Extreme cold events were defined as ≥2, ≥3, or ≥4 consecutive days with daily mean temperature ≤4.5°C (the 10th percentile of the study-period distribution). Quasi-Poisson distributed-lag non-linear models were used to estimate cumulative relative risks over lag 0-14 days. Pollutant-related effect modification was evaluated using stratified analyses and interaction measures.

Overall, extreme cold events were not significantly associated with pediatric asthma outpatient visits. However, stronger associations were observed during periods with higher CO and SO₂ concentrations. For lag 0-14 days, cumulative relative risks for ≥2-day cold events were 2.60 (95% CI: 1.13-5.95) in the higher-CO stratum and 3.41 (95% CI: 1.15-10.11) in the higher-SO₂ stratum. Similar patterns were observed for longer cold-event definitions. Multiplicative interactions were identified for both CO and SO₂, whereas additive interaction evidence was clearer for CO. Other pollutants showed less consistent modification patterns.

The association between extreme cold events and pediatric asthma outpatient visits may depend on concurrent gaseous pollutant conditions. Relatively elevated CO and SO₂ may help identify cold-event periods with greater pediatric asthma outpatient burden.