Children’s visits to the emergency room for serious food-allergy reactions may be on the rise, if the experience of one major U.S. medical center is an indicator.

Researchers at Children’s Hospital Boston found that the number of food-induced allergic reactions treated in their ER more than doubled over six years - from 164 cases in 2001, to 391 in 2006.

There was an even sharper increase in the number of more serious, and sometimes life-threatening, reactions known as anaphylaxis. Signs and symptoms of anaphylaxis include skin reactions like hives and flushed or pale skin; nausea, vomiting or diarrhea; dizziness or fainting; difficulty breathing; and a sudden drop in blood pressure that can lead to shock.

In 2001, the current study found, there were 78 cases of food-induced anaphylaxis; in 2006, that number was 207.

That corresponded to a rate of 15 anaphylaxis cases for every 10,000 ER visits in 2001, and a rate of 38 per 10,000 in 2006, the researchers report in the Journal of Allergy and Clinical Immunology.

The reasons for the increases cannot be gleaned from the data. But the findings are in line with studies pointing to a general increase in food allergies among U.S. children in recent years, first author Dr. Susan A. Rudders told Reuters Health in an email.

According to the U.S. Centers for Disease Control and Prevention, 3 million school-aged children in the U.S. had a food allergy in 2007, which was up 18 percent from 10 years earlier.

Among the most common triggers of children’s food allergies are peanuts and tree nuts - such as almonds, walnuts and cashews - milk and eggs.

No one is sure why food allergies are being increasingly diagnosed, Rudders said. One theory, she noted, is that changes in diet may be at work; another theory, known as the “hygiene hypothesis,” holds that today’s clean living - creating less exposure to germs from early life on - may in some people make the immune system more prone to attacking normally benign substances, like food proteins and pollen.

It is not yet clear whether the rise in ER visits for serious food reactions seen in this study points to a wider trend. Rudders said that this appears to be the first study looking specifically at ER visits for serious food reactions, and further research at other centers is needed.

A limitation of the current study is that it was a review of medical records, and the researchers could not test the children to confirm that they had a food allergy. Food-related allergies were defined as symptoms suggestive of an immune-system reaction after a child had reportedly been exposed to a food allergen.

Anaphylaxis was defined as a reaction involving at least two organ systems in the body, or a sudden drop in blood pressure alone.

If the current findings can be extrapolated to other U.S. medical centers, Rudders and her colleagues write, that would mean that the number of ER visits spurred by food allergies each year is actually much higher than has been estimated. An often-quoted statistic, they note, is that severe food reactions send 30,000 Americans to the emergency room every year.

SOURCE: Journal of Allergy and Clinical Immunology, online July 10, 2010.