Abstract
BackgroundEmergency department (ED) visit and hospital admissions (HA) data have been an indispensible resource for assessing acute morbidity impacts of air pollution. ED visits and HAs are types of health care visits with similarities, but also potentially important differences. Little previous information is available regarding the impact of health care visit type on observed acute air pollution-health associations from studies conducted for the same location, time period, outcome definitions and model specifications.MethodsAs part of a broader study of air pollution and health in St. Louis, individual-level ED and HA data were obtained for a 6.5 year period for acute care hospitals in the eight Missouri counties of the St. Louis metropolitan area. Patient demographic characteristics and diagnostic code distributions were compared for four visit types including ED visits, HAs, HAs that came through the ED, and non-elective HAs. Time-series analyses of the relationship between daily ambient ozone and PM2.5 and selected cardiorespiratory outcomes were conducted for each visit type.ResultsOur results indicate that, compared with ED patients, HA patients tended to be older, had evidence of greater severity for some outcomes, and had a different mix of specific outcomes. Consideration of ‘HA through ED’ appeared to more effectively select acute visits than consideration of ‘non-elective HA’. While outcomes with the strongest observed temporal associations with air pollutants tended to show strong associations for all visit types, we found some differences in observed associations for ED visits and HAs. For example, risk ratios for the respiratory disease-ozone association were 1.020 for ED visits and 1.004 for ‘HA through ED’; risk ratios for the asthma/wheeze-ozone association were 1.069 for ED visits and 1.106 for ‘HA through ED’. Several factors (e.g. age) were identified that may be responsible, in part, for the differences in observed associations.ConclusionsDemographic and diagnostic differences between visit types may lead to preference for one visit type over another for some questions and populations. The strengths of observed associations with air pollutants sometimes varied between different health care visit types, but the relative strengths of association generally were specific to the pollutant-outcome combination.
Highlights
Emergency department (ED) visit and hospital admissions (HA) data have been an indispensible resource for assessing acute morbidity impacts of air pollution
Results by age and poverty area We considered models stratified by age and by poverty area (Figures 3 and 4, in tabular form in Additional File 3: Table S3 and Additional File 4: Table S4) to examine whether these factors explained some of the variation in associations by visit type
For the pneumonia-ozone relationship, the associations were strongest in the 0–1 year age group, and in that age group the association was stronger for HAs than for ED visits (RR = 1.076, 95% confidence interval (CI) = 0.9601.207) but the estimates were imprecise
Summary
Many time-series studies have found associations between daily ambient air pollution levels and acute exacerbations of cardiovascular and respiratory diseases [1,2,3] These studies commonly use the daily count of health care visits for selected conditions as the measure of morbidity in the population. Important differences between ED visits and HAs may impact their usefulness for addressing particular questions, and the magnitude and interpretation of observed air pollution-health associations. Some of these differences reflect medical need for the different types of services offered in these two settings. For example EDs may be used for primary care to a greater extent by those who, for economic reasons, have difficulty accessing primary care services [11,12]
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