ATLANTA—The 1996 Summer Olympic Games in Atlanta provided researchers with a rare opportunity to observe the positive impact that decreased automobile traffic can have on pediatric asthma. Because of citywide efforts to reduce such traffic during the games, the rate of childhood asthma episodes requiring acute care fell dramatically for a short time, a recent ecological study by the Centers for Disease Control and Prevention (CDC) found.[1]

To reduce traffic, Atlanta implemented a number of measures, including providing around-the-clock public transportation, adding 1,000 buses to the existing fleet, and closing downtown city streets to private cars. Further, local business owners altered their downtown delivery schedules and eased the morning rush hour through flexible work schedules and telecommuting. The result: marked declines in ozone and other air pollutants known to trigger asthma exacerbations.

EXPANDING ON THE EXISTING EVIDENCE

“This study builds on the evidence supporting air pollution’s detrimental effect on asthma,” said lead author Michael S. Friedman, MD, an epidemiologist in the Air Pollution and Respiratory Health Branch of the National Center for Environmental Health at the CDC in Atlanta. “It also shows that many asthma exacerbations requiring acute care can be prevented when we all work together,” he added.

Data collection occurred during the four weeks before the 1996 Olympics (baseline), the 17 days of the games (July 19 through August 4), and the four weeks after the games (follow-up). The study population included children ages 1 to 16 years living in the five central counties of metropolitan Atlanta. Because of their central location, these counties were especially likely to exhibit dramatic air quality changes in response to reduced automobile traffic, the authors noted.

The primary outcome measurement was the number of hospitalizations and emergency department and urgent care center visits for asthma. Data on such events came from the Georgia Medicaid claims file, the patient database of a local health maintenance organization (HMO), two of three Atlanta pediatric hospitals, and the Georgia Hospital Discharge Database, which contains hospitalization records from all metropolitan Atlanta hospitals.

Children with a primary diagnosis of asthma who were admitted to a metropolitan Atlanta hospital during the study were assumed to have had an asthma event that required acute care. So were children with the same primary diagnosis who visited an emergency department or urgent care center during the study, whether or not they were hospitalized.

Data on atmospheric levels of ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, and particulate matter of 10 µm or less (PM10) were provided jointly by the Environmental Protection Agency and the Environmental Protection Division of Georgia’s Department of Natural Resources.

The data were gathered from three air-quality monitoring sites within metropolitan Atlanta’s central counties. None of these sites was capable of measuring all of the air pollutants studied, but together they could cover all five.

To determine what effect weather has on air pollution, the authors obtained hourly readings of wind speed, solar radiation, temperature, barometric pressure, and relative humidity, from a state-run weather monitoring station east of downtown Atlanta. A mean was calculated for each variable using readings from 6 AMto 6 PM. Total daytime levels of mold, the predominant summertime allergen in Atlanta, were available for the weekdays of the study period from the Atlanta Allergy and Asthma Clinic.

To assess traffic changes, the authors contacted the Georgia Department of Transportation to get the one-hour morning peak and total 24-hour traffic counts from four sites within Atlanta. These counts were available for most of the study days. Public bus and rail-line use was also examined, with the Metro Atlanta Rapid Transit Authority providing average weekday and weekend passenger totals for the study period.

LOWER TRAFFIC VOLUME

A decrease occurred in overall traffic volume during the 1996 Olympics, as shown by a 2.8% decline in the 24-hour traffic counts on weekdays. There were especially large drops in the one-hour morning peak traffic counts, which fell 22.5% on weekdays and 9.7% on weekends. “That is important,” commented Dr. Friedman, “because many of the pollutants we studied are released by cars during the morning rush hour and then turned into ozone later in the day.”

Atlanta’s one-hour peak ozone level declined nearly 28%, from a daily mean of 81.3 parts per billion (ppb) at baseline to 58.6 ppb during the Olympics. Of the other pollutants studied, only concentrations of sulfur dioxide increased during the Olympics (by about 22%). There were reductions in levels of all of the other pollutants ranging from about 7% to nearly 19%.

Declines in the ratio of children requiring acute care for asthma varied widely by data source, said Dr. Friedman—but all the declines were striking. They included drops of about 44%, 42%, 19%, and 11%, respectively, among children identified through the HMO database, the Georgia Medicaid claims file, the Georgia Hospital Discharge Database, and the two pediatric emergency departments.

Only the findings for the Georgia Medicaid claims file reached statistical significance; the others approached significance. Air quality and acute asthma episodes in children returned to their pre–Olympic Game levels during follow-up, when traffic resumed its normal patterns. In practical terms, the decreased asthmalpha-exacerbation rates seen during the 17 days of the Olympic Games meant that between seven and 30 fewer children than usual required acute care. During that same period, there was virtually no change in the rate of non–asthmalpha-related events requiring children to get acute care, which suggests that there were no important changes in the study population or use of emergency medical services during the Olympics. Therefore, it is unlikely that the decreased asthma morbidity in this study simply resulted from children with a primary diagnosis of asthma leaving Atlanta during the Olympics, the authors said.

WAS THE WEATHER A FACTOR?

The improvement in Atlanta’s air quality during the Olympics could not have been due mainly to weather changes that discourage the buildup of ozone and other pollutants, Dr. Friedman said in an interview with PULMONARY REVIEWS. Indeed, none of the weather variables or mold counts studied changed significantly from baseline. Further, a multivariate regression analysis controlling for weather variables still found a significant reduction (13%) in ozone levels.

Indirect evidence against changes in weather includes a significant correlation between the traffic counts and one-hour peak ozone level. Because of the decrease in traffic volume, particularly during the morning rush hour, emission of ozone precursors was reduced, the authors explained.

Weather probably did not have much to do with carbon monoxide concentrations, either, they suggested, since levels of that pollutant depend primarily on automobile emissions. The small rise in sulfur dioxide was consistent with the larger number of diesel-powered buses in operation at the time and should not have occurred if weather conditions were inhibiting air pollution. Therefore, “at least 50% of the improvement in air quality we found was related to reduced automobile emissions,” Dr. Friedman said. And the reduced emissions translated directly into fewer asthma exacerbations.

—Timothy Begany

Reference
1. Friedman MS, Powell KE, Hutwagner L, et al. Impact of changes in transportation and commuting behaviors during the 1996 Summer Olympic games in Atlanta on air quality and childhood asthma. JAMA. 2001;285:897-905.

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