Programs & Campaigns

The Air We Breathe: Children, Cars and Asthma

By Beverly Rockhill, PhD

The ever-changing media headlines attest to medicine’s endless search for the ‘causes’ of various diseases. Given the large amounts of research time and taxpayer money spent on uncovering the causes of major diseases, one might wonder whether any of the existing knowledge regarding disease cause and prevention is ever put into widespread practice or public health policy. For various social, political and economic reasons, there is, unfortunately, a huge gap between knowledge about what causes disease and implementation of knowledge to prevent disease.

This commentary is focused on asthma, on some important things we know about it and about what we could be doing to prevent it.

Asthma is a disease of the airways, manifested as a narrowing of the air passages. It is episodic, with acute attacks interspersed with symptom-free periods. Asthma has become a significant public health problem in the U. S. It is a leading cause of childhood illness, affecting an estimated 7% of American children under age 18.

Numerous studies have documented an increase in its prevalence although there is currently no scientific consensus on the cause(s) of this increase.

There is currently much scientific research on the causes of asthma, including gene research. However, because the rates of asthma - especially in children - have gone up so dramatically in recent decades in the U.S. and other industrialized countries, we shouldn't look to genes for the sole explanation - human genes have not changed appreciably in recent decades. Instead, it is likely that the precipitating causes of asthma can be found in exposures that have themselves changed dramatically over time. For example, there is strong evidence that prevalence and severity of childhood asthma could be reduced if air pollution from vehicle emissions were reduced.

In a recent article in the Journal of the American Medical Association (February 21, 2001), researchers provided data on an interesting ‘natural experiment.’ Michael Friedman, a physician associated with the Centers for Disease Control and Prevention in Atlanta, GA, and four colleagues studied the impact of changes in driving behavior and traffic patterns on air quality and on childhood asthma attacks during the 1996 Summer Olympic Games in Atlanta. While previous studies have found positive associations between traffic density on street of residence and asthma prevalence, the impact of citywide automobile use and traffic flow on ambient air pollution and asthma attacks had not been studied before.

To prepare for the summer Olympic Games, community leaders in metropolitan Atlanta designed a strategy to minimize traffic congestion, which included an integrated 24-hour-a-day public transportation system, the addition of 1,000 buses for park-and-ride services, local business use of alternative work hours and telecommuting, closure of downtown to private automobile travel, and altered downtown delivery schedules.

The first fundamental question is did such efforts actually have any effect on air quality? Vehicle exhaust is a leading source - sometimes the leading source - of ambient air pollution in metropolitan areas, along with industrial exhaust and power generation plants. Compared with emissions from non-vehicle sources, the relative amounts of nitrogen oxides, carbon monoxide, and small particulate matter have increased disproportionately in recent decades due to the large increase in worldwide automobile use, according to Friedman et al.

The researchers found that morning peak traffic counts decreased by 22.5% -the equivalent of 4,260 fewer vehicle trips - on the four major Atlanta highways during the Olympics, compared to the four weeks before and after the Games. Was this decrease in traffic enough to bring about a reduction in air pollution? Friedman et al found a strong relationship between daily traffic volume and ozone levels: the decreases in morning traffic limited the buildup of ozone precursors, or ‘building blocks,’ early in the day. Without a sufficient concentration of these precursors, rapid ozone production and accumulation could not occur later in the day, during the time of maximum heat. Using measurements of air quality obtained from EPA monitoring, Friedman et al found that ozone concentrations declined by almost 30% during the Olympic Games, again compared to the four weeks before and after the Olympics. There were also large reductions in daily carbon monoxide levels, particulate matter concentrations, and nitrogen dioxide levels.

The question then becomes: Were the decreases in traffic and air pollution that occurred during the Olympics associated with a reduction in severe asthma attacks in children during the same period? The researchers looked at hospital records for two groups of children - those receiving Medicaid and those enrolled in HMOs. Among the Medicaid group, the number of severe asthma attacks, defined as those requiring either emergency room treatment or actual hospitalization, decreased by almost 50%, from an average of 4.23 events per day (total: 118.44) during the four weeks before and after the Olympics, to 2.47 events per day (total: 69.16) during the Olympics. Among children enrolled in HMOs, the number of asthma-related emergencies decreased by a similar amount. Could it be that during the excitement and hubbub of the Games, people did not seek medical care as frequently as usual? In other words, did asthma attacks decline simply because all types of hospital visits declined? While this possibility seems unlikely, the researchers examined it to add strength to their conclusions. They found that there was little or no change in hospitalizations and emergency room visits for non-asthma events during the Olympics.

The researchers’ evidence strongly suggests that reductions in air pollution levels led to a reduction in childhood asthma incidents in Atlanta during the Olympics. In the authors' own words (p. 903), "...our findings suggest that by decreasing automobile emissions through citywide changes in transportation and commuting practices, a substantial number of asthma exacerbations requiring medical attention can be prevented." Most importantly, the results from this study say something about both the EPA's air quality standards and the way we view disease treatment in the U.S. This study shows that air pollution levels lower than the current EPA allowable levels are indeed achievable through concerted effort on the parts of communities, and that these lower levels may be necessary if our society is to make serious inroads in preventing asthma (and possibly other respiratory problems) in children.

Commentary:

Why did this well-conducted scientific study receive relatively little attention from researchers, policy makers, and the media?

The analysis was well designed and well executed, and passed the rigorous peer-review process of the Journal of the American Medical Association. Its findings are in agreement with a large body of evidence on the effects of air pollutants on respiratory function in humans. It is virtually impossible to dismiss the study as flawed.

However, the implications of this study's findings, that decreasing vehicle traffic would help prevent childhood asthma, demand a degree of political and social will and commitment to public health that seem all too rare in this country. When actions that might improve public health conflict with ‘individual needs’ (in this case, the desire of individuals to buy and drive whatever vehicle they want as often as they want; the resistance of individuals to having their tax dollars go to fund public transportation; and the rights of major corporations to freely market, sell and profit on increasingly large, inefficient vehicles), it is often hard for arguments about potential ‘collective benefit’ to be heard.

It is much easier to give an individual with asthma an inhaler or a pill or even a hospital bed, or to spend money on researching genetic causes or new treatments of the disease, than it is to question prevailing social norms in the attempt to prevent the disease in the first place.

Missing is the fundamental question of the rights of all individuals to an environment that is kept as healthy as possible by those with stewardship over the human environment - our government officials. Obviously, not all individuals exposed to high levels of air pollution from cars get asthma - in fact, only a small minority do.

However, most diseases, including respiratory conditions such as asthma, are part of a continuum of ill-health - there are few diseases in which an individual goes from being completely healthy to being seriously ill. There are usually many gradations of ‘feeling ill’ that lie in between, even if these gradations don't receive an official medical diagnosis. Many people, while not developing respiratory problems severe enough to warrant the diagnosis of asthma, may develop coughing, wheezing, and other breathing ailments after exposure to air pollutants. These individuals, along with the comparatively smaller minority with diagnosed asthma, stand to benefit from improvements in air quality. This is especially true of the most vulnerable segments of the population: the very young and the very old.

While an ‘individual-focused’ strategy of giving asthma medication to asthmatics is now our only solution, a ‘population strategy’ of reducing air pollution from traffic makes sense from a broad public health standpoint - because many individuals, those with asthma and those with other, perhaps undiagnosed, respiratory problems, stand to benefit. - end -    

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