Examining vulnerabilities to thunderstorm-associated asthma in Atlanta, Georgia

Introduction. Associations between thunderstorm activity and asthma morbidity have been reported in numerous locations around the world. In Atlanta, we previously observed an association between daily counts of asthma emergency department (ED) visits and thunderstorm occurrence, in which asthma visits were 3% higher on days following thunderstorms. This effect was modified by rainfall and wind gusts, such that associations between asthma and thunderstorms were only observed for thunderstorms with rainfall or wind gusts. These results provided preliminary evidence in support of certain hypotheses regarding the thunderstorm-asthma relationship: 1) pollen grains rupture by osmotic shock in rainwater, releasing allergens; and/or 2) gusty winds from thunderstorm downdrafts spread particles and/or aeroallergens, which may ultimately increase the risk of asthma attacks. However, a further understanding of our previous findings is necessary, especially with projections of increases in heavy rainfall, thunderstorm events and aeroallergen concentrations as the climate system warms. In particular, an understanding of which populations are vulnerable to the effects of thunderstorms on health is imperative for prevention and preparedness planning activities. In the current analysis, we assessed the association between asthma exacerbation and thunderstorm occurrence for several population subgroups.

Methods. We identified asthma exacerbations using ED visits to 20-county Atlanta-area hospitals over the 1993 to 2004 time period with primary International Classification of Disease, 9th revision diagnosis codes 493 and 786.07. Thunderstorm occurrence data were obtained from the automated surface observing system station at the Atlanta Hartsfield–Jackson airport, which recorded 564 thunderstorm days (12.9% of 4383 total study days). We assessed the association between thunderstorms and next day asthma ED visits using Poisson generalized linear models, controlling for long term temporal and seasonal trends and meteorological conditions with cubic splines. To assess population vulnerability, we considered analyses stratified by several sociodemographic and spatial descriptors. As a preliminary spatial descriptor, we defined a 650 km2 sub-area encompassing 22% of the 20-county population; this area is bordered by a highway that envelopes the inner city and the airport where thunderstorm occurrence data were recorded.

Results. We observed 215,832 asthma ED visits during the study period. On days following thunderstorms, we observed 24,350 visits for asthma, of which 54% were by patients <=8 years of age, 51% were by female patients, and 27% were by patients residing inside the pre-defined sub-area. Preliminary analyses suggest that the risk of thunderstorm-related asthma exacerbation is similar across different age groups, with modestly stronger associations in young adults (19-34 years of age), and is stronger for males than for females. Restricting the study area to patients residing inside the sub-area did not affect the overall findings. Results of other spatial analyses and analyses considering race and socioeconomic descriptors will be presented.

Conclusions. Overall, our findings suggest that specific population subgroups may be more vulnerable to the impacts of thunderstorms and related exposures on asthma exacerbation than the overall asthmatic population. Our findings also provide some support for using central airport thunderstorm measurements to represent exposures over the very large study area.