Asthma, a chronic inflammatory disease of the airways, has become a national epidemic. According to the Centers for Disease Control, asthma afflicts more than 13.7 million Americans, including an estimated 2.3 million Californians. What's more, death rates from asthma have been steadily rising over the last 20 years, despite improvements in medication. Increases in asthma rates, along with increases in hospitalization and death rates, have been particularly sharp in urban areas and among African-Americans.
Children are particularly vulnerable to asthma. In fact, it is now the most common childhood illness in the United States, as well as the leading cause of school absences due to illness. More than 5 million American children are estimated to have asthma, half a million of them in California. From 1990 to 1997, 144 children died of asthma in the state.
Asthma and Air Pollution
Environmental factors, particularly poor air quality, trigger many asthma attacks. (Whether they cause asthma is not yet clear.) Children are extremely vulnerable to the effects of air pollution, because they breathe in more air per pound of body weight than adults do, and because they breathe more rapidly and more deeply. And, since children's airways are narrower than adults', inflammation causes a proportionately bigger reduction in air flow.
What kind of air pollution contributes to asthma attacks? The list is long. In the outside air, most triggers are produced by the combustion of fossil fuel. The components of smog -- airborne particles, sulfur oxides, and ground-level ozone -- are all asthma triggers, and the Bay Area continues to experience violations of health standards for ozone and particle pollution.
Indoor air also abounds with substances that can lead to attacks, including nitrogen oxides (from unvented gas appliances), volatile organic compounds (substances that evaporate from paints, solvents, new carpets, and building materials), tobacco smoke, and pesticides. Dust mites, cat and dog allergens, and mold are also frequent triggers. In recent years, as buildings have become "tighter," more of these pollutants have been trapped inside.
The Limitations of Relying on Hospitalization Rates
Although scientists have learned a great deal about asthma, its risk factors, and its triggers, there are still large gaps in their knowledge. Still missing are detailed data about asthma's prevalence and, especially, its incidence -- that is, about how many people have asthma and how many new cases develop each year. In the Bay Area, as in the rest of the country, this information is not systematically tracked. In its absence, scientists have turned to hospitalization records -- the records NRDC researchers analyzed.
The decreases in asthma hospitalization rates they found between the periods 1991 to 1994 and 1995 to 1997 in the Bay Area are good news. But there are inherent limitations in relying on hospitalization records to analyze asthma rates. Hospitalization data offer only a rough idea of how asthma affects children, rather than the detailed picture that careful tracking of asthma's prevalence and incidence would provide. By definition, hospitalization rates reflect only the worst cases of asthma, so children with less severe cases who don't seek treatment at a hospital will never even be recorded. The results are further skewed because people who lack health insurance or a family physician are more likely to delay getting medical care for their children's asthma until they end up in the hospital. Moreover, the records don't separate out multiple admissions for the same patient.
It's possible that the drop in hospitalizations is a result of improved access to preventive health care or better education about using medication. It's even possible that the decrease reflects an actual decrease in childhood asthma in the Bay Area. But because scientists lack good data on the number of asthmatic children in the region, they cannot be sure of the reason for the decrease. And no matter what the correct interpretation turns out to be, the fact remains that in the Bay Area, childhood asthma rates remain distressingly, dangerously high.
Research on asthma continues, but much of it is focused on treatment, rather than on efforts to understand asthma's causes or prevent its occurrence. For example, the U.S. Department of Health and Human Services' updated asthma target for 2010 focuses almost entirely on treatment. In light of asthma's continuing prevalence, prevention deserves far greater attention.