The Association Between Asthma Hospitalizations and Air Pollution in Virginia, 2005

Introduction:  Asthma is one of the most common chronic diseases in the United States, with increasing prevalence over the past twenty years.  From 1980 to 2004, the estimated prevalence of asthma in the U.S. population increased from 3.1% to 13.2%.  During 2004, asthma was responsible for 497,000 hospitalizations in the U.S.; 9,460 in Virginia.  Between 2004 and 2005 asthma hospitalizations in Virginia increased by 5% to 9,955 hospitalizations; 495 additional hospitalizations from the previous year. EPA recognizes ozone and particulate air pollution as significant triggers for asthma symptoms in children and adults.  In Healthy People 2010, the U.S. Department of Health and Human Services cites asthma as a major clinical and public health concern. The reduction of environmental exposures that contribute to events such as asthma hospitalizations is listed as one of the key national health objectives in this national framework for disease prevention. Even though there is evidence through clinical and epidemiological studies that air pollution is associated with diminished lung function and asthma exacerbations, it remains an underappreciated health threat.

Objectives:  The objective of this study was to evaluate the association between asthma hospitalizations and concentrations of ozone and particulate matter in Virginia for 2005.  This study also looked for possible synergistic effects of multiple air pollutants on asthma hospitalizations and at the seasonal and geographic associations.

Methods:  Air pollution data for particulate matter (PM 2.5) and ozone concentrations for 2005 were obtained from the Virginia Department of Environmental Quality (DEQ).  Hospital discharge data for 2005 were obtained from the Virginia Health Information (VHI) Hospital Discharge Database through the Virginia Department of Health.  All admissions with asthma as the primary diagnosis were identified for patients who reported residing in one of five study locations. Data were aggregated by week of admission and location for comparison with aggregated air quality data.  Data were analyzed using SPSS and SAS.  Descriptive statistics, bivariate correlations and multiple linear regression analyses were conducted.  Poisson regression was used for the final model to adjust for a low rate of outcome.

Results:  The asthma admission rate was highest for Henrico County, followed by Roanoke, Hampton, Madison, and Fairfax County.  A significant inverse correlation was found between asthma admissions and ozone and and between asthma hospitalization rates and ozone and PM2.5 levels in Henrico and Fairfax counties and between asthma hospitalization rates and ozone in Madison county.  Significant predictive relationships were found between the asthma hospitalization rate during the spring season in the locations of Henrico and Roanoke.
 
Conclusion:  The findings of this exploratory ecological analysis suggest that concentrations of PM2.5 and ozone are not useful as predictors of asthma hospitalizations in Virginia.  Future research should include multiple years of data and use different measures of asthma morbidity to determine whether there is a relationship between air pollution and asthma morbidity in Virginia.