She's only age 5, but Octavia Vanlandingham has been treated at the Johns Hopkins emergency room about 50 times.
Since she was diagnosed with asthma as an infant, the ailment has been a major factor in her lifestyle: She limits contact with the family cat, uses an inhaler twice a day and has wheezing attacks that make it hard to take in air.
"Sometimes I can't breathe at all," she said.
Octavia is one of 5 million children in the United States with a disease that has reached near-epidemic proportions - in adults and children - over the past 20 years.
Between 1980 and 1996, the number of asthma cases nearly doubled nationwide. The Centers for Disease Control and Prevention says 16 million people suffer from it, or about 1 in 12 people. "This disease is getting worse," said Dr. Darryl Zeldin, a scientist at the National Institute of Environmental Health Sciences.
Asthma is a chronic disease characterized by recurrent inflammation of the lungs that makes it difficult to breathe.
Nationwide, summer heat prompts a spike in asthma attacks, as sunlight cooks emissions from factories and cars, creating ozone that irritates the lungs.
But in Maryland, the worst spikes occur in September and October, when children return to school, spend more time indoors and are exposed to the viral infections common in crowded classrooms.
"There's both an environmental and a seasonal component to it," said Dr. Carol Blaisdell, a researcher at the University of Maryland Medical Center who studies asthma rates in Baltimore.
Cause is unknown
No one knows what causes asthma. But it disproportionately targets children and minorities, kills 5,000 people a year in the United States and costs the nation $6 billion a year for treatment. Worldwide, the number of asthmatics is expected to jump from 300 million to 400 million in the next 20 years.
"The main thing is, it ain't going away," said Dr. Peter S. Creticos, an asthma researcher and clinical director of the Johns Hopkins Asthma and Allergy Center.
Many asthmatics apparently inherit the disease from a parent. Octavia's mother and older sister, for example, are asthmatic.
But other victims have no genetic predisposition, and researchers say nailing down a cause is proving difficult because of the variety of symptoms and triggers - and the divergent ways that our lungs and immune systems respond to stress.
"It turns out the immune system is far more complicated than we thought," said Dr. Norman Edelman, chief medical adviser for the American Lung Association and dean of the medical school at State University of New York at Stony Brook.
Attacks are irregular
Asthma attacks can be occasional or frequent. They can be brought on by exertion, poor air quality, ragweed or a range of common allergens, including dust mites, cockroaches, mice and the dander of cats and dogs.
Zeldin released a survey this month showing that 82 percent of all U.S. homes have detectable levels of mouse allergen - contained in the animals' waste and saliva. The survey checked 831 homes in 75 randomly selected communities.
"The problem is there's so many potential triggering mechanisms out there," he said. "When you block one immune pathway that may trigger asthma, another one opens up somewhere else."
Researchers began focusing on asthma about 10 years ago when officials at CDC and other researchers first noted the jump in cases.
"Asthma's been a very sought-after disease, in terms of finding treatments, because it's such a serious health threat," said Dr. Jack Elias, a Yale University researcher.
Elias' study, published June 11 in Science, concluded that chitinase, an enzyme that attacks the protective coatings on shellfish, may hold promise in treating asthma. The Yale researchers showed that blocking chitinase in asthmatic mice drastically cut lung inflammation.
They also found that in humans, chitinase was absent from healthy lungs while it was present in the lungs of asthmatics.
Researchers at the University of Southern California examined the health records of 3,500 children who played outdoors in Southern California in 2002 and found those in high-ozone areas more susceptible to asthma.
A 2001 study in the Journal of the American Medical Association found a ban on car traffic in downtown Atlanta during the 1996 Olympics lead to a 44 percent decline in asthma-related treatments in hospitals and health care centers.
Other studies have linked asthma to the absence of open-air ventilation in modern buildings. Several years ago, researchers began arguing the "hygiene hypothesis," that some children develop asthma because they aren't exposed to enough pathogens early in life for their immune systems to fully develop.
But experts remain stumped as to what exactly causes asthma and how it attacks the body.
'We have no answers yet'
"We have a lot of information, but we have no answers yet," said Ernst Spannhake, a researcher at the Johns Hopkins Bloomberg School of Public Health.
But some health officials are fighting back with innovative measures.
Octavia is one of 600 city children treated by the Breathmobile, a 34-foot-long recreational vehicle purchased with grants two years ago by the University of Maryland Hospital for Children.
Equipped with an examining room, it is staffed by a nurse, a nurse practitioner and a health technician who doubles as a driver. The Breathmobile visits about 20 city schools and recreation centers every month to six weeks. Foundation grants cover the van's $400,000 annual cost. Similar vans operate in Phoenix, Chicago and Los Angeles.
"If we didn't see these kids, a lot of them would probably never be diagnosed," said Dionne Mebane, a nurse practitioner.