Mold and ragweed allergies on the rise in the U.S.

By Dr. Ananya Mandal, MDMay 26 2011

Allergies are on the rise and it is noted that more numbers of Americans sensitive to ragweed and mold. Phoenix, Las Vegas and the Riverside-San Bernardino area are among the 30 worst affected areas with this allergy.

The study is nationwide and is to be released by Quest Diagnostics Health Trends. It identifies the U.S. cities where allergies to ragweed and mold are most common, based on test results for allergens nationwide. In the study, results of close to 14 million blood tests from more than 2 million patients taken over a four-year period were evaluated. The tests looked for high levels of sensitivity to 11 common allergens, including ragweed, mold, two types of house dust mites, cats, dogs and five foods. Those sensitive to mold were most plentiful in Dallas, Riverside-San Bernardino, Phoenix, Los Angeles and Chicago.

The researchers note that sensitization to ragweed and mold increased 15% and 12%, respectively, over the study's four years. That's consistent with recent research suggesting that rising carbon dioxide levels in the atmosphere are causing a dramatic increase in the release of ragweed pollen, while rising temperatures promote an increase in birch tree pollen, a major allergen in Europe. The study also suggests that environmental allergy sufferers -- now almost 1 in 5 Americans -- have a longer season of suffering, another apparent result of climate change.

The authors of the study say that the increased mold allergies are linked to climate change is particularly worrisome. Mold allergies exacerbate asthma and are a key trigger of allergic sensitization they warn. Overall, the regions of the country most affected by ragweed allergies were the Southwest, Great Lakes states, mountain states and the Plains. Allergy rates were lowest in the Southeast and Northwest.

Study author Stanley Naides of Quest Diagnostics' Nichols Institute in San Juan Capistrano, Calif. Said, “The level of sensitization to these common allergens is increasing. These kinds of studies where we have access to large databases are very helpful in defining questions for further studies.” Numbers may be even higher since many people with allergies never get tested, says Naides.

“The highest areas are in the Southwest, and one has to raise the question of whether weather is contributing to this," said Naides. “We believe this is the first large national study to show that the growing prevalence of allergies, suggested by other studies, is largely due to increases in environment-based allergens previously associated with climate change.” He said more research is needed to confirm such theories.

Princess Ogbogu,, assistant professor of medicine and pediatrics at The Ohio State University, “It's hard to say that it's 100% climate change.” She called for a decade-long study for more details and also noted that researchers did not test for tree pollen and grass sensitivity. Susan Schuval, a pediatric allergist at Cohen Children's Medical Center in New Hyde Park, N.Y., says the study is impressive in size and scope, and confirms what allergists are seeing in practice. She cautions that the study looks only at blood testing, which she says has about a 15% to 20% false positive rate.