Changes in Timing of Spring Onset and Increased Risk of Asthma Hospitalization in Maryland: Harbinger of Climate Change

Abstract

Introduction: The proposed association between climate change and increased burden of allergic diseases are based on three different thematic observational studies that have linked i) increased CO2 concentration with higher pollen production, ii) warmer air/surface temperatures with early spring onset and longer pollen season, and iii) higher pollen exposure with increased risk of asthma hospitalizations. Yet empirical evidence collectively linking climate change with pollen season and asthma exacerbation is still lacking.Methods: We used general additive (GAM, quasi Poisson), and mixed effect (negative binomial) models to investigate the association between changes in timing of spring onset (SOS)- detected using satellite observation - and risk of asthma hospitalization in Maryland during 2001-2012. To characterize the underlying mechanism, we further investigated the relationship between changes in SOS and springtime tree pollen dynamic (timing of pollen season onset, timing and intensity of peak pollen concentration, and pollen season length).Results: In the unadjusted model, very early (Incident Rate Ratio (IRR): 1.17, 95% Confidence Interval (CI): 1.07-1.28) and late (IRR: 1.07, 95% CI: 1.00-1.15) onset of spring were associated with increased risk of asthma hospitalization. When the analysis was adjusted for extreme heat event and PM2.5 concentration, the risk remained significant for very early SOS (IRR: 1.10, 95% CI: 1.02-1.20), but not for late SOS (RR: 1.03, 95% CI: 0.97-1.11). We further observed that very early SOS is significantly associated with the length for Birch and Oak pollen season (p<0.05).Conclusion: Our results show that ongoing changes in timing of spring onset that are tied to climate variability and change increases risk of asthma hospitalization. Our result serve as a wake-up call to public health and medical communities regarding the need to anticipate and adapt to the ongoing changes in the timing and severity of the spring allergy season.