Despite improvements in air quality and decreases in cigarette smoking, the number of Americans diagnosed with asthma is on the rise, according to the U.S. Centers for Disease Control and Prevention.

Tuesday is World Asthma Day, and the CDC has released a new report that shows the number of people diagnosed with asthma in the United States has grown by 4.3 million between 2001 and 2009. That means as of 2009, 1 in 12 Americans live with the inflammatory disorder. And although there is an increase in diagnoses among all demographic groups, the report notes a higher percentage of children have asthma than adults, specifically about 9.6 percent compared to 7.7 percent, respectively.

“The trend has been gradually rising over this decade,” said Dr. Paul Garbe, chief of CDC's Air Pollution and Respiratory Health Branch. “We still see almost 3,500 people die each year with asthma, which is 3,500 more than should be.”

An increase in asthma diagnoses means an increase in medical costs. In 2002, asthma-related medical costs added up to about $53 billion. By 2007, that number jumped 6 percent to about $56 billion.

“That translates into over $3,330 per person,” Garbe said.

Garbe went on to say that asthma complications also mean a loss of productivity in the workplace and an increase in emergency room visits. The CDC also reports that 2 in 5 asthma sufferers are uninsured, making it hard to obtain medications.

CDC officials said they don’t have an explanation for the growth in asthma rates, but they continue to spread awareness, noting treatment and prevention is a key to keeping the disease under control since asthma is a chronic illness. Symptoms include wheezing, breathlessness, coughing and chest tightness.

There isn’t a cure for asthma, but patients can control symptoms with inhalers and prevent attacks by avoiding triggers.

Triggers are often environmental -- such as mold, pet dandruff and pollution. One of the most common is secondhand smoke.

"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," Garbe said. "While we don't know the cause of the increase, our top priority is getting people to manage their symptoms better."

CDC officials said asthma attacks aren’t inevitable, and they can be controlled with the proper treatment and education.

Elizabeth Prann currently serves as a Washington-based correspondent for Fox News Channel (FNC). She joined the network in 2006 as a production assistant. Click here for more information on Elizabeth Prann