Air Pollution-Related ER Visits Vary by Age, Respiratory Illness

The Centers for Disease Control and Prevention (CDC) has conducted the first nationally relevant study of association between air pollutants and emergency department (ED) visits across patient ages and respiratory illnesses.

"Studies of emergency department visits related to respiratory illness in the United States have been mostly confined to single city studies," Heather Strosnider, PhD, MPH, team lead of Science Development in the Environmental Health Tracking Section, Division of Environmental Health Science and Practice, Center for Environmental Health, CDC, explained in discussing the study with MD Magazine^®.

"While such studies are informative, differences in air pollution composition and population characteristics may limit their generalizability across the nation," she said.

The data sets used in establishing national ambient air quality standards for the Clean Air Act have traditionally been drawn from national vital statistics and Medicare utilization records, which describe mortality and hospitalization among adults 65 years and older.

"Hospitalizations typically represent more severe cases of adverse respiratory outcomes and are more common among older individuals," Strosnider pointed out.

The lack of data for individuals under 65 years of age, and data coming principally from single city studies, Strosnider and colleagues point out, "is a particularly important issue for respiratory ED visits, because the vast majority of these visits occur in people under age 65 years."

To capture patterns of ozone and fine particulate matter (<2.5mm aerodynamic diameter [PM_2.5]) levels with respiratory ED visits across age groups and respiratory illnesses in a nationally representative sample, the investigators drew on daily air measures from the Environmental Protection Agency (EPA) and the ED data for 894 counties in 17 states, representing 45% of the US population (138.5 million individuals). The assessment period extended from 2000-2014, with states having data available for periods ranging from 3-13 years.

The investigators stratified data by the age groups of children <19 years; adults 19-65 years; older adults >65 years; and all ages combined.

Respiratory conditions, excluding chronic obstructive pulmonary disease (COPD) in children, were: acute respiratory infection (ARI) including upper respiratory infections, bronchitis, and bronchiolitis; asthma; COPD; and pneumonia.

Strosnider and colleagues calculated the rate ratios (RR) per 10mcg/m³ increase in PM_2.5 and all respiratory visits of 1.024 among children; 1.008 among adults; and 1.002 among older adults. With 20 ppb increase in ozone, RR was 1.017 among children; 1.051 among adults; and 1.033 among older adults.

The investigators noted that the associations varied in magnitude by age group and respiratory condition. For ozone, they observed significant and positive associations with ARI, COPD, and pneumonia for all ages except for asthma among older adults. The highest magnitude RR for ozone was asthma among adults (RR 1.065). The risks were generally highest among adults—except for ARI, where the RRs for adults and older adults were similar. The risk for the association between ozone and ARI among children was elevated and significant, but lower than for adults and older adults.

For PM_2.5 , the investigators found positive, significant associations for asthma and ARI for all ages combined and for each age group; and for pneumonia in all ages combined in one of the 2 analysis models. In contrast to the associations with ozone, they found less variation in the RR with PM_2.5 by age group for asthma and ARI, and a significant association with pneumonia only among adults.

"Our study provides robust estimates of the effects of air pollution similar to the estimates provided by previous multi-city studies of mortality and hospitalizations among people 65 years and older," Strosnider commented.

Strosnider and colleagues declared that, by examining associations with ozone and PM_2.5 for people of all ages across hundreds of counties in the US, "we address a key gap in the evidence used to inform national ambient air pollution policy."

The study, "Age-Specific Associations of Ozone and Fine Particulate Matter with Respiratory Emergency Department Visits in the United States," was published online in the American Journal of Respiratory and Critical Care Medicine.