Assessment of Asthma Prevalence in Relation to Air Quality Indicators

Objectives: A retrospective ecological study was conducted to determine whether asthma prevalence rates were lower in locations with less severe air pollution as measured by commonly used air quality indicators. Methods: Using bivariate linear correlation, county-level rates of current asthma prevalence were compared with the U.S. EPA air quality Design Values (DV) of five air pollutants and American Lung Association ozone and Particulate Matter scores for over 100 U.S. counties from the 2005 and 2012 time periods. Using the same method, changes in asthma prevalence between 2005 and 2012 were compared with concurrent changes in DVs for PM2.5 and ozone. A multiple linear regression was also used to assess the relationship between the air pollutant DVs and asthma prevalence in the 2012 time period. Graduated symbol maps of the U.S. mainland were developed to reveal any obvious geographic patterns among pollutant levels and asthma rates. Results: Absolute values of Pearson correlation coefficients (R) were less than .18 in all but one of the comparisons. The exception was the comparison of changes in ozone DVs and asthma prevalence between 2005 and 2012; the correlation coefficient for this analysis was .283 and significance level was .008, which indicates that the general decrease in ozone DVs was subtly but significantly associated with the overall increase in asthma prevalence. The multiple linear regression analysis and graduated symbol maps were consistent with the general results that lower levels of air pollution do not correspond geographically to lower asthma prevalence. Conclusions: This study suggests that U.S. EPA DVs and ALA scores are not reliable predictors for the prevalence of asthma at different locations in a single timeframe. This finding raises a question about the suitability of these air quality indicators as metrics for healthful air quality. The finding that the asthma prevalence increase was associated with the decrease in ozone DVs between 2005 and 2012 deserves further investigation.