Asthma prevalence still surging, CDC says

Urbanization is the main culprit, experts say

The number of Americans suffering from asthma has skyrocketed since 1980. An April 24 report from the Centers for Disease Control and Prevention in Atlanta notes a 75% increase in the number of self-reported cases of asthma and a 160% increase among children under age 5. While the report has no direct explanation for the dramatic rise, experts are focusing on one prime culprit: urbanization.

"Asthma is principally a disease of childhood and a disease of the western industrialized lifestyle, just like coronary disease, high blood pressure and so on," says Scott Weiss, MD, MS, professor of medicine at Harvard Medical School and director of respiratory and environmental epidemiology at the Channing Laboratory of Brigham and Women's Hospital in Boston. "Estimates are that the prevalence is increasing at 5% a year; that's a big number."

Weiss said the increase is not the result of an escalating presence of allergens. "In particular, there is a decrease in bacterial infections and an increase in obesity, perhaps changes in dietary composition. All these are contributing to the development of an increased incidence and prevalence of asthma."

CDC notes geographic, racial disparities

David Mannino, MD, a medical epidemiologist and pulmonary medicine specialist with the CDC in Atlanta, agrees with the urbanization theory and offers a further explanation.

"Since the oil crisis of the mid-'70s, we have constructed 80% of our buildings with no windows that open," he said. "We are much more dependent on ventilation systems."

Mannino thinks the tightening of buildings, including schools, the congestion of cities, crowded housing, and outdoor and indoor air pollution provide a clue to the upsurge that has sent the prevalence and mortality rates soaring.

Meanwhile, Norman Edelman, MD, senior scientific consultant for the American Lung Association in New York City and professor of medicine, physiology, and biophysics at the State University of New York in Stony Brook, says, "The most honest answer, I believe, is that nobody really knows."

Edelman rules out risk factors such as outdoor air pollution and smoking, since the incidence of both risk factors is decreasing. However, he says, the prevalence of day care and its corresponding crowded conditions and increased risk of respiratory infections is important, as is the stereotypical underprivileged urban home where crowding and the presence of cockroaches, another important risk factor, can trigger the disease.

The heavily industrialized Northeast accounts for nearly the twice the asthma rates experienced in the less densely populated West, while for patients aged 5 to 34, the regional difference was nearly threefold.

The CDC offers "possible reasons" for these regional disparities, among them: differences in treatment and physician diagnosis; access to health care; climatic and home heating factors; and exposure to air pollutants.

Mannino theorizes that the Northeast may have a higher prevalence because more people seek treatment since managed care plans are more common there.

The CDC report shows some significant statistical disparities between the black and white populations in terms of treatment. Both groups are inclined to visit doctors' offices for treatment, but the white rate of emergency room treatment for asthma increased by only 10% from 1992 to 1995, while the rate at which blacks complaining of asthma visited emergency rooms zoomed by 58% during the same period.

The number of whites hospitalized for asthma actually decreased over the same time period by nearly 6%, while the black hospitalization rate soared by nearly 72%.

Yet Weiss says to typify asthma as a disease of urban black children is an oversimplification.

"I think it is complicated to understand what's going on with the urban poor in the U.S. and how that relates to the asthma epidemic, because asthma prevalence is increasing in all races and all socioeconomic strata of our society," he said. "What isn't clear is the people in the inner city who are minorities get less good care and may have more exposures."

Edelman another answer may be found in the increasing numbers of parents using day care centers and their propensity to spread another well-known asthma trigger: early childhood respiratory viruses.

The same conditions, and a few others, exist in the typical environment of the poor in the United States, Edelman says. "If you look at poverty and ask me what to guess, I would guess it's crowding, which increases transmissibility of respiratory viruses and antigens like cockroaches."

That, coupled with a general absence of preventive treatment for the poor, means children receive care mainly when they are in a crisis, and little or no regular anti-inflammatory treatment to prevent attacks. "There is a lot in the minority environment that predisposes to poor asthma care with kids winding up in hospitals and probably an increased risk of death," he said.

Asthma is far more dangerous to blacks of all ages than whites.

Black women over the age of 35 living in the highly industrialized Northeast have by far the greatest risk of death with asthma as the underlying cause.

The mortality rate among blacks climbed by 130% between 1979 and 1995. Females bore the brunt of the burden with a 122% increase. During the same period, the death rate among whites climbed a substantial 86%. While prevalence was lowest for those aged over 35, that age group accounted for 85% of the deaths.

Mannino said the mortality rates are "driven" by high death rates in New York City and Chicago, and further studies of medical examiners' reports may provide more information about mortality in those cities. "Linking the asthma rate to poverty has not been ruled out," he said.

Weiss said the racial disparity is directly attributable to the availability of health care. In Sweden, a small country with universal health care and a comparatively small socioeconomic spread, prevalence has almost doubled but hospitalization rates have been stable in the past 10 years.

"They're managing pretty well [in terms of prescribing medication]," he said. "But I think in the U.S., with a huge number of disenfranchised people and 40 million people who don't have adequate health care, we've got bigger problems."

Physicians more likely to diagnose asthma

Experts agree the failure to obtain treatment for a variety of reasons, among them socioeconomic, may be a factor in the escalating prevalence of asthma. Some also say doctors are now more likely to give a primary diagnosis of asthma than in years past because it is more easily treatable.

"Physicians are now more likely to call wheezing or bronchial infection asthma," Mannino says. "Most asthma is treated by general practitioners, and education has certainly changed the way asthma is treated."

The National Asthma Education and Prevention Program was designed to encourage physicians to stop treating asthma as a reactive disease and to treat it with anti-inflammatory agents to address the underlying cause of the problem.

Despite new treatment methods, Mannino says, "Patients don't feel better if they're taking anti-inflammatories. Patients are looking for immediate relief." As a result, patients often pressure physicians for additional medication, and "end up making a bad situation worse."

Edelman says preventive asthma treatment requires a "team approach" involving the child, parents, teachers and physician. "These plans are very efficacious. They cut down on asthma attacks, they cut down on visits to emergency rooms," he says.

The medical profession is doing many things right and some things wrong, Edelman says.

"Asthma still is a highly undiagnosed disease among children. Physicians are not picking it up. It can be subtle, a kid who coughs after he exercises, lots of colds and allergies. What we are doing incorrectly is underdiagnosing asthma," he says.

"There is still evidence that there is less than optimal use of inhaled anti-inflammatory medications," he says. "Guidelines from the National Heart Lung and Blood Institute are very, very clear. But it's still a minority of physicians who actually use the guidelines," he adds.

Edelman continues, "What the profession is doing right is that all the things I mentioned are getting better. There is a much more intense effort for the comprehensive approach, to teach children how to use their inhalers. There is an increased use of inhaled anti-inflammatories but just not enough."

PCPs fail to refer asthma patients

The jury is still out on whether managed care is providing better treatment or not, Edelman says.

On one hand, it is in the economic interest of managed care providers to keep asthma sufferers out of hospitals, so there is a greater focus on preventive care, he says. On the other hand, managed care plans often are behind the times when it comes to adding the newest and best treatments to their formularies, and primary care physicians are less apt to refer moderate-to-severe asthma sufferers to specialists when they are needed, Edelman adds.

Susan Banks-Schlegel, PhD, a researcher at the National Heart, Lung and Blood Institute in Bethesda, MD, which funds asthma research, says the volume of current research is encouraging.

"It takes a long time between scientific observation and putting it into medical practice, but with clinical research developments, we are looking at a rapid translation of research into practice."

Numerous potential new treatments are "in the works," she said. "But still we are at the bench making the transition to the bedside."

For more details, contact the Centers for Disease Control and Prevention, 1600 Clifton Road NE, Atlanta, GA 30333. Telephone: (404) 639-3311.