THURSDAY, Jan. 29 (HealthDay News) -- St. Louis is now the 2009 "Asthma Capital of the United States," according to the Allergy and Asthma Foundation of America's annual ranking of the 100 most challenging places to live for people with the respiratory disorder.

Ranked ninth in 2008, St. Louis went to the top of this year's list due to a number of factors, including a higher than average pollen score, continued poor air quality, and a lack of 100 percent smoke-free laws, the foundation said.

City rankings are based on analysis of 12 factors in three areas: prevalence factors (illness and mortality statistics); risk factors (such as air quality, pollen, 100 percent smoke-free laws, and poverty); and medical factors (medication usage and access to specialists).

The other top asthma capitals for 2009 are: Milwaukee, Wisc.; Birmingham, Ala.; Chattanooga, Tenn.; Charlotte, N.C.; Memphis, Tenn.; Knoxville, Tenn.; McAllen, Texas; Atlanta; and Little Rock, Ark.

The annual report is meant to call attention to the asthma epidemic in the United States and to encourage cities to improve the quality of life for residents with asthma.

Asthma, which affects more than 20 million children and adults in the United States, is one of the most common and costly diseases in the country, according to a foundation news release. Since every city has a variety of risk factors, people with asthma need to have a good asthma management plan no matter where they live.

More information

The U.S. National Heart, Lung, and Blood Institute has more about asthma.