Associations of asthma and allergic rhinitis with climate data, Florida, 2005-2012
Climate is one of many factors-including changes in case definitions, reporting practices, and environmental pollutants-which may impact allergic respiratory disease rates. Future climate projections indicate increasing average temperatures and more extreme events. However, the extent to which climate variability will impact human cases of these and other diseases is uncertain. As part of a larger initiative to understand the health effects associated with climate hazards in Florida, we sought to characterize the relationship of climate, as characterized by monthly air temperature and drought indices, with rates of asthma and allergic rhinitis ED visits.
METHODS: In Florida, the Agency for Health Care Administration (AHCA) has been collecting ED data since 2005, including detailed records of each visit, the primary and contributing diagnoses, patient demographics, and billing information. These data allow for study of non-notifiable diseases, like asthma and allergic rhinitis. This analysis includes visits to Florida EDs made by Florida residents from 2005 to 2012 for cases with asthma (ICD-9 code 493) or allergic rhinitis (ICD-9 code 477) listed as the primary diagnosis or contributing diagnosis. Statewide crude rates for monthly asthma and allergic rhinitis ED visits were calculated between January 2005 and December 2012, using annual population estimates.
State-wide monthly climate data, including monthly average temperatures (degrees Fahrenheit) and several drought indices, were obtained from the National Climatic Data Center (NCDC) for the period of study. Although several different drought indexes are available, the Standardized Precipitation Index (SPI) is recommended for studying environmental health outcomes in the Eastern US because the index can project emerging droughts sooner than other indexes. The SPI considers only precipitation and represents the probability of recording a given amount of precipitation. Zero indicates median precipitation. Progressively drying conditions are represented with negative numbers, and wet conditions are positive. Although both the one-month (SPI1) and two-month (SPI2) indexes are measures of short-term drought, the SPI2 provides a slightly longer time horizon for analysis. SPI values are categorized as follows: extremely wet (2.00 and above); very wet (1.50 to 1.99); moderately wet (1.00 to 1.49); near normal (-0.99 to 0.99); moderately dry (-1.00 to -1.49); severely dry (-1.50 to -1.99); extremely dry (-2.00 and below). Categorical SPI1 and SPI2 data were approximately normally distributed, but slightly skewed toward wetter conditions in Florida. Since monthly counts of ED visits were modeled as the dependent variable, Poisson regression is used to test the association between SPI1, SPI2, and average temperature, while adjusting for year and month. P-values are reported.
Asthma: From 2005 to 2012, the number of asthma-related ED visits increased by 24.2% for primary diagnoses (from 75,944 to 100,142) and by 29.9% for contributing diagnoses (from 219,144 to 312,608). Wet conditions were mostly protective for or not associated with increased asthma-related ED visits. For example, an extremely wet SPI2 is protective for both primary and contributing asthma-related ED visits (p-value <0.0001). However, a very wet SPI2 increased the risk for both asthma as a primary (p-value <0.0001) and contributing (p-value =0.0426) diagnosis. Drought conditions were mostly protective for or not associated with increased asthma-related ED visits. However, a very dry SPI1 (p-value <0.0001) and an extremely dry SPI2 (p-value = 0.0237) increased the risk for primary asthma-related ED visits. For ED visits with a primary asthma diagnosis, temperature decreased risk, and for ED visits with a contributing asthma diagnosis, temperature increased risk.
Rhinitis: From 2005 to 2012, the number of allergic rhinitis-related ED visits increased by 40.8% for primary diagnoses (from 3,156 to 5,327) and by 52.3% for contributing diagnoses (from 7,232 to 15,169). Moderately wet (both p-values <0.0001) and moderately dry (both p-values <0.0200) SPI1 conditions were protective for both increased primary and contributing allergic rhinitis-related ED visits. Wetter SPI1 and moderately wet SPI2 conditions increased the risk for allergic rhinitis-related ED visits. Drought conditions were mostly protective for or not associated with increased allergic rhinitis-related ED visits. For example, a very dry SPI 2 is protective for both primary and contributing allergic rhinitis-related ED visits (p-value <0.0001). For all rhinitis related ED visits, temperature significantly increased risk.
CONCLUSIONS: In the United States, the diagnoses of asthma and allergic rhinitis have increased significantly in the last few decades due to a combination of increased medical and community awareness and changes in environmental and social conditions. In Florida, poorly controlled asthma and allergic rhinitis, as measured by the crude rate of ED visits, also increased between 2005 and 2012. Even when controlling for the annual and seasonal variations in ED visits for either disease, increasing temperatures, more frequent droughts, and more extreme precipitation events are likely to place additional burdens on the healthcare system in Florida. Although dryer conditions were protective for allergic rhinitis-related ED visits, increased temperatures, and associated extended pollen season, may increase risk for Floridians with uncontrolled allergic rhinitis in the future. The inconsistent associations between SPI and asthma-related ED visits may indicate that more extreme precipitation and temperatures could have unexpected impacts on increasing rates of asthma-related ED visits. Further investigation is needed to characterize the relationship between climate factors, regional disease burden, and other environmental stressors.