Homing in on Asthma
Asthma in children has skyrocketed in the last two decades, and it hits inner-city children especially hard. Now researchers from the Bloomberg School and Hopkins’ School of Medicine are zeroing in on the role indoor pollution plays in provoking asthma attacks.
In a paper published in February in Environmental Health Perspectives, the researchers reported that higher levels of indoor particulate matter in the home were positively correlated with higher incidences of asthma attacks in children already suffering from asthma.
What causes some people to develop asthma in the first place still isn’t understood. Neither is the reason for the doubling of asthma rates from the 1980s to the 1990s. Minority and inner-city children are hardest hit: 12.8 percent of black children suffer from asthma, compared with 7.9 percent of whites. And black children are more likely to visit the emergency room because of asthma, and are also much more likely to die.
“We’re focusing on kids because that’s where the morbidity is the greatest,” says study co-author Patrick Breysse, professor of Environmental Health Sciences. Breysse is director of the Johns Hopkins Center for Childhood Asthma in the Urban Environment. Last year the Bloomberg School received $12 million from the National Institute of Environmental Health Sciences (NIEHS) to continue the center’s funding.
For the study, Breysse, PhD ’85, MHS ’80, and Gregory Diette, MD, associate professor of Medicine and of Epidemiology, working with six other Hopkins colleagues, chose 150 asthmatic children between the ages of 2 and 6 from East Baltimore. Most of the participants were poor and African-American, and most lived in aging single-family rowhouses. Diette says that the houses ranged from immaculately clean and well-maintained to deteriorating and poorly kept.
At baseline, at three months and six months, they had a technician take air samples in the child’s bedroom over a three-day period. The children were also examined by researchers at those three times, and parents filled out questionnaires about asthma symptoms.
The researchers found that high indoor concentrations of particulate matter increase asthma symptoms. Although this study didn’t analyze the sources of the particles, previous work has shown that they come from a variety of sources, including outdoor pollution, cooking, smoking, pets and mice. (In general, coarse particulate matter contains more dust and animal dander, while fine particulate matter is likely to come from sources such as car exhaust.)
Because the researchers were interested in whether fine and coarse particles might have different effects, they measured separately fine particles (2.5 microns or smaller) and coarse particles (between 2.5 and 10 microns). They found that the different particle sizes did in fact affect asthma symptoms independently, and also in different ways.High levels of coarse particulate matter increased the number of days of coughing, wheezing or chest tightness, as well as the number of days that medication had to be used for an attack.
High levels of fine particulate matter had similar effects—but were also associated with more asthma symptoms brought on by exercise, even when the exercise was away from the home. Although it’s not clear exactly how, it seems that the hyperventilation associated with exercise is more likely to induce an asthma attack when the child has also been exposed to fine rather than coarse particles. That may be because the finer particles are small enough to penetrate to the alveoli, the structures of the lungs responsible for gas exchange, says Diette.
The findings of this study could help explain at least part of the reason that inner-city children have higher asthma rates. Previous studies have found that particulate matter concentrations in urban homes in Baltimore were three times higher than those in the suburbs. In the present study, 85 percent of the children lived in homes that would fail to meet National Ambient Air Quality Standards.
Not only are overall particulate levels higher, but the composition of the particles is different. Inner-city asthma sufferers are more likely to have a smoker in the house. And they are more likely to be exposed to allergens in the form of mouse urine and cockroach feces. This is important because asthma is associated with allergies, and inhaling allergens probably has something to do with severity of asthma symptoms.
Diette says that there is probably no single answer to asthma. “It’s not a simple condition. It is aggravated and provoked by many different factors. Controlling one of them is not enough to turn the process off,” he says.
Says Breysse, “The questions we’re trying to ask now are: What can we do to make the asthmatic child’s environment different, and can we show that these changes improve asthma?”
So in other studies the Center is testing comprehensive approaches to improving the indoor environment. That includes testing children for allergies, managing mice and cockroach infestations, reducing smoking in the homes, eliminating pets, and providing air conditioning and air filters.
Breysse says that researchers at the center also want to study what role diet might play in asthma. And Diette and others are trying to determine if there is a genetic link that affects onset and severity of the illness.
“In the best case, we might be able to identify who is susceptible to specific environmental triggers. It would be nice to know in advance whether a person is prone to have asthma, or to allergy problems with cats, cockroaches or mice,” Diette says.