Effects of cumulative exposures to extreme weather events on children respiratory system

Background: The ongoing climate change is exacerbating extreme weather events. Literature reports much evidence of the short-term effects of extreme climate on health. In contrast, the long-term effects of cumulative exposures to climatic extreme events remain understudied, with children being particularly vulnerable due to their developing respiratory system. 

Hypothesis: The study aims to delineate the effect of cumulative extreme events occuring in the first 6 years of life on children's respiratory health, assessed at age 7. 

Data: The study drew on the NINFEA cohort, a web-based birth cohort comprising 7500 mother-child pairs across Italy, recruited between 2005 and 2016. We calculated individual exposure by linking the residential history with the ERA5-land dataset provided by the Copernicus program of the European Centre for Medium-Range Weather Forecasts (ECMWF) for maximum (Tmax) and minimum (Tmin) temperature and cumulative precipitation (Pr) data. 

Respiratory health was collected at age 7 as wheezing symptoms in the last 12 months reported by the mothers.  

Method:Exposure to extreme weather events was identified as number of days in the 6 years of life above predetermined thresholds, defined with three  approaches: 

[a] The fixed value definition identifies the threshold using a value in the variable unit. 

[b] The percentile definition uses the location-specific normal series (1971-2000) to obtain the k-th percentile, allowing us to consider the geographical adaptation. 

[c] The day of the year (DOY) percentile definition uses the location-specific and day-specific normal series (1971-2000) to pick up the DOY-specific threshold; the extreme is located in a spatio-temporal definition addressing spatial and seasonal characteristics. 

Multiple thresholds were applied within each method to limit exposure's potential misclassification.

Analyses were adjusted for spatio-temporal confounders (macro-region, urban/rural classification, Koppen-Geiger climate zone, year of birth) and individual factors (maternal age, education, asthma).

Results: A consistent adverse effect of heat on respiratory health was captured using the fixed-value definition for both temperature extremes (OR= 1.011 for Tmax ≥35°C [C.I. 1.001-1.021]) and precipitation (OR= 1.006 for Pr ≥30mm [C.I. 1.001-1.011]). The percentiles analysis showed similar results, though with larger confidence intervals, reducing precision (OR= 1.007 for Tmax ≥95°[C.I. 0.999-1.015]; OR= 1.012 for Pr ≥95°[C.I. 0.998-1.025]). DOY percentile analysis,stratified by season, suggested clear effects of maximum temperatures in winter, spring, and autumn, but not in summer, and of minimum temperatures in summer, spring, and autumn, but not in winter. Stronger effects were detected with increasing threshold values, suggesting a threshold blurring or dose-response effect.

Conclusion: This study highlights the potential long-term impact of exposure to extreme weather events on children's respiratory health, emphasizing the need for mitigation measures against CC.