About 8.2 percent of Americans had asthma in a 2009 national survey of about 40,000 individuals. That's nearly 25 million people with asthma, according to a Centers for Disease Control and Prevention report.
The rate had been holding steady at a little under 8 percent for the previous four years.
Better diagnostic efforts could be part of the reason for the increase. They were believed to be a main reason for an increase in asthma seen from 1980 through 1995, said Dr. Lara Akinbami, a medical officer at the CDC's National Center for Health Statistics.
Asthma is a chronic disease involving attacks of impaired breathing. Symptoms may include coughing, wheezing, and chest pain. It can be fatal: Health officials estimate more than 3,000 U.S. asthma deaths occur each year.
But treatment seems to be improving, with 52 percent of asthma patients in the 2009 survey saying they suffered an attack in the previous year, down from 60 percent at the beginning of the decade.
Asthma is more common among women than men. It's also more common in children, blacks, Puerto Ricans, people living below the poverty level, and people in the Northeast and Midwest, according to the CDC.