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MADISON, N.J. — Ragweed and mold are driving increased allergies across America, Quest Diagnostics reported Monday.
In the study, sensitization rates to common ragweed and mold increased the most of the 11 common allergens evaluated over a four-year period. Sensitization to common ragweed grew 15% nationally, while mold grew 12%. By comparison, sensitization to the 11 allergens combined increased 5.8%.
"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," Quest Diagnostics medical director of immunology Stanley Naides said. "Given concerns about a warming climate, additional research is needed to confirm these findings and assess the possible implications for public health."
Between 10% and 20% of Americans are sensitive to ragweed. Increased exposure to ragweed has been shown to increase an individual's risk of developing a ragweed allergy or of experiencing more severe allergy symptoms. Research has shown that a warming climate, by promoting longer blooming seasons, may increase both the abundance of certain environmental allergens, including ragweed, in the environment and length of the year during which people are exposed. A study published in March 2011 in the Proceedings of the National Academy of Sciences determined that the ragweed season was nearly a month longer in 2009 than it was in 1995 in certain northern areas of North America, possibly as a result of climate change.
Mold, as a precipitation-affected aeroallergen, also may increase in prevalence with a warmer climate.
The Quest Diagnostics study also ranked the 30 most populous metropolitan areas in the United States for immunoglobulin-E, or IgE, sensitization to ragweed. In the "30 Worst Big Cities for Ragweed" ranking, Phoenix; Las Vegas; Kansas City, Mo.; Riverside-San Bernardino, Calif.; and Dallas showed the highest rates of ragweed sensitization. Miami; San Francisco; Portland, Ore.; Tampa, Fla.; and San Diego showed the lowest. Those cities at the high end of the ranking showed sensitization levels nearly three times higher than those at the low end.
On a regional basis, ragweed sensitization was highest in the Southwest, Great Lakes, and Mountain and Plains states. The investigators theorized that the differences in ragweed sensitization regionally and in the most populous cities may in part be due to longer and more intense ragweed pollen seasons, but they also underscored that the reasons behind these differences are unclear and deserve additional study.
"Considering that the ragweed season traditionally begins in August, Americans suffering from ragweed allergies should expect a very long summer," Naides said. "These individuals, as well as those with other allergies or asthma, should take proactive measures to reduce their exposure to ragweed over the next several months."
The study was based on nearly 14 million test results from more than 2 million patient visits.