Early results from the largest cross-sectional national allergy study ever conducted, to be released later this week, suggest that allergies have increased in America, but that most of the increase was due to two environmental allergens, ragweed and mold. The study, based on nearly 14 million test results from more than 2 million patient visits, is believed to be the largest to suggest that increased prevalence of the two allergens, which have been associated with climate change, are largely responsible for an increase in allergies in the United States.
The Quest Diagnostics Health Trends™ Report, Allergies Across America™, from Quest Diagnostics (NYSE: DGX), evaluates results of ImmunoCAP® specific Immunoglobulin E (IgE) blood testing to 11 common allergens, including common ragweed and mold, two house dust mites, cats and dogs, and five foods. A high IgE sensitization level for a specific allergen tested is highly suggestive of an allergy, although physicians also evaluate symptoms, medical history and other factors in order to clinically diagnose an allergy.
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,” said Stanley J. Naides, M.D., medical director, immunology, Quest Diagnostics. “Given concerns about a warming climate, additional research is needed to confirm these findings and assess the possible implications for public health.”
About 10% to 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, may also increase in prevalence with a warmer climate.
The Quest Diagnostics study also ranked the 30 most populous metropolitan areas (“cities”) in the United States for IgE sensitization to ragweed. In the “30 Worst Big Cities for Ragweed” ranking, Phoenix, Las Vegas, Kansas City, Riverside-San Bernardino in California, and Dallas showed the highest rates of ragweed sensitization, while Miami, San Francisco, Portland, Tampa, and San Diego showed the lowest. Those cities at the high end of the ranking showing 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 difference 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,” said Dr. Naides. “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.”