Nearly 11 percent of Hawai'i children have asthma, the second-highest percentage in the nation, according to a report released yesterday by the Centers for Disease Control and Prevention.

Vog from Big Island volcanoes long has been a likely suspect in the state's higher rate of asthma, a chronic respiratory disease characterized by attacks of difficulty breathing.

Hawai'i County has the highest rate of asthma in the state, but researchers say the problem also is found in areas not prone to vog, suggesting other factors, such as genetics and smoking.

"I don't think vog is the answer," said Dr. Wallace Matthews of the Kapi'olani Medical Center for Women and Children. He said Hawai'i's climate allows plants to bloom and spread pollen year-round, and there is increasing evidence of genetic differences that may make certain Asian populations and other ethnic groups more suspectible to the disease.

Other asthma triggers include cockroach dander, dust mites and mold, also prevalent here.

Asthma program coordinator Gregg Kishaba of the state Department of Health said so far there are no certain causes for the asthma problem in Hawai'i, and that a number of research projects are under way to provide some answers. Increased awareness of the disease among physicians and patients could be one reason there are more cases being reported, he said.

The CDC report also shows that the death rate for children with asthma has declined since 1999, while doctor visits for the condition have more than doubled over the past decade.

The report did not provide mortality data for individual states, but Health Department statistics show that the number of asthma-related deaths in Hawai'i dropped from 3.77 per 100,000 residents in 1991 to 1.69 deaths in 2002, when there were 21 asthma-related deaths.

State data also show a slight decline in hospitalization rates of children with asthma, whose symptoms include shortness of breath, coughing, wheezing, and chest pain or tightness.

The CDC report notes that "a major frustration in fighting asthma is the mystery of its development. It remains unknown why some people get the disease and others do not."

Matthews, a pediatric pulmonologist, said the "hygiene theory" is an emerging factor in the development of allergies and asthma. With today's emphasis on germ-killing and cleanliness, many children aren't exposed at an early age to as many allergens and irritants.

"Their immune system isn't as tuned up as it used to be to fight everything," he said. So, the body can overreact to allergen and other substances in the environment, which may lead to asthma.

Parental smoking is another important factor in childhood asthma, according to Matthews.

"Kids who have parents who smoke have worse asthma," he said. "And smoking outside the house doesn't help because it sticks to your hair and clothes."

Maintenance and "controller" medicines such as inhaled steroids have been effective in reducing the frequency and severity of asthma attack, he said. They also prevent permanent lung damage that can result in adult respiratory disease.

With proper medication and monitoring, there's no reason children with asthma can't live normal, active lives, Matthews said.

Reach Christie Wilson at cwilson@honoluluadvertiser.com.