A Centers for Disease Control and Prevention Vital Signs report says the reason for the growth in asthma rates is unknown.
The report says healthcare costs for asthma grew from about $53 billion in 2002 to about $56 billion in 2007, about a 6 percent increase -- or $3,300 per person -- in medical expenses. About 2-in-5 uninsured and 1-in-9 insured people with asthma could not afford their prescription medication.
"Despite the fact that outdoor air quality has improved, we've reduced two common asthma triggers -- secondhand smoke and smoking in general -- asthma is increasing," Paul Garbe, chief of CDC's Air Pollution and Respiratory Health Branch, says in a statement. "While we don't know the cause of the increase, our top priority is getting people to manage their symptoms better."
Asthma triggers are usually environmental -- including tobacco smoke, mold, outdoor air pollution and infections linked to influenza, cold-like symptoms and other viruses, Garbe says.
Asthma diagnoses increased among all demographic groups during the study period, although the increase was greater among children than adults. Asthma rates were highest among boys and blacks, the report says.