Food Allergies Overestimated by Public; Need Careful Confirmation

Becky McCall

December 15, 2010

December 15, 2010 (Dubai, United Arab Emirates) — Food allergies are markedly overestimated by the general public. According to challenge-confirmed studies, the medically confirmed prevalence is far lower than what the public believes. Self-diagnosed allergies are claimed by 20% to 30% of the general public, whereas clinically confirmed cases have been identified in less than 6% of children and less than 2% in adults, food allergists reported here at the World Allergy Organization (WAO) 2010 International Scientific Conference.

Sami Bahna, MD, chief of the Allergy and Immunology Section at Louisiana State University Health Sciences Center in Shreveport, and 2009/10 president of the American College of Allergy, Asthma and Immunology, led a session on the diagnosis and treatment of food allergy.

"The public claim allergy for any adverse or undesirable reaction to food. There's a misguided tendency among the general public to think that if they get undesirable symptoms after a meal, they have an allergy. People easily suspect food allergy after having eaten something that disagrees [with them], but the reaction may be due to something else entirely," he told Medscape Medical News.

According to Dr. Bahna, numerous studies from different parts of the world have shown that allergy skin testing or blood testing for specific immunoglobulin (Ig)E antibodies is good for screening but not optimally confirmative or exclusive.

Commenting on Dr. Bahna's presentation, Alessandro Fiocchi, MD, from the University of Milan Medical School and Fatebenefratelli/Melloni Hospital in Milan, Italy, and head of the WAO Special Committee on Food Allergy, agreed that food allergies are overestimated.

"Food allergy science is based on the challenge and confirmation of self-reported findings. . . . A study published recently in the Journal of Allergy and Clinical Immunology, which evaluated the prevalence of food allergy to milk, egg, and peanut, showed that the prevalence was around 2% in the world population in different age ranges," he told Medscape Medical News.

Dr. Fiocchi said that the prevalence of self-reported allergy reaches 30% in surveys of various populations, although he added that it depends on the formulation of the question in the different studies. "The prevalence of confirmed food allergy can be estimated to be up to 8% in children younger than 3 years and about 1% to 2% in adults."

He noted 2 studies that estimated the prevalence of food allergy and/or intolerance in adults using double-blind placebo-controlled food challenge. In the Netherlands, the self-reported frequency was 12.4%, and in the United Kingdom, it was 20.4%. An adverse reaction was confirmed in only 0.8% and in 1.4% to 1.8%, respectively.

He added that EuroPrevall, a European birth cohort study, will soon release final results on food allergy prevalence. "So far they have discovered that at most, one fifth of self-reported food reactions are actually positive for allergy through a double-blind challenge. So we conclude that when an individual believes they have a food allergy, they should go to a doctor for a proper diagnostic test; otherwise, they'll be exposed to a full elimination diet."

Identifying real cases of food allergy relies on a combination of history and immunologic testing, Dr. Bahna explained. He raised concerns related to confirming claims of food allergy and the reliability of tests, including the skin prick test and specific IgE tests.

"I want physicians to diagnose allergy appropriately by taking a thorough medical history, just like a police detective. Maybe the patient's suspicions are incorrect. We need to ask the right questions, such as: When and where did it happen? What did you do just before it happened? When it happened previously, were the same preceding factors present? What manifestation did you get?'" he said. He added that "such information may be more valuable than allergy tests."

Manifestations of food allergy are typically acute urticaria, angioedema, eczema, wheezing, abdominal pain, vomiting, diarrhea, or systemic anaphylaxis. Food allergy is not known to cause depression, fatigue, abnormal behavior, learning dysfunction, or neurologic disorders.

Dr. Bahna emphasized that food allergy is often blamed for a wide range of symptoms that can be caused by a variety of diseases, including psychologic disorders. Some laboratory tests might initially be required to check for nonallergy causes. To screen for food allergy, skin testing is the most commonly used procedure, but in some cases blood testing for specific IgE antibodies is preferred.

"If the skin prick tests or IgE tests are positive, the individual is considered sensitized. The stronger the test result, the more likely the food is truly an offending food, especially if it correlates with the patient's history," Dr. Bahna pointed out. He added that "the most definitive test to confirm a certain food as causing the clinical reaction is the elimination-challenge test to document that the symptoms disappear by avoiding that food and recur when the food is eaten."

Addressing the issue of the predictive value of the skin prick test and the specific IgE tests, Dr. Bahna referred to his own studies and to several by other researchers. He showed data demonstrating the remarkable variation between studies. He attributed these inconsistencies to differences in patients' ages, type of manifestation, and severity of allergy.

He warned that skin prick and IgE tests need to be interpreted with care. "A positive skin test or specific IgE serum test merely indicates sensitization that may or may not be clinically relevant. A negative test does not rule out allergy because the antibodies are concentrated in the target organ and may be minimal in the circulation or healthy skin."

Dr. Bahna advised considering multiple factors when interpreting skin testing or specific IgE results. These include the total IgE level, the patient's age, the type of allergy manifestation, the severity of allergy manifestation, the food allergen, the degree of exposure to the food, and the duration of avoidance of the food prior to testing.

According to numerous studies cited by Dr. Bahna, the challenge test confirmed that only about 30% of the suspected foods were truly causing the symptoms and only half of patients suspected of having food allergy were allergic to a food.

To avoid bias, Dr. Bahna recommends that the challenge test be done in a blind, placebo-controlled fashion, particularly in older children and adults. Once the truly offending foods are identified, an elimination diet would be easy to follow to control symptoms. The immune system is likely to overcome such hypersensitivity, and tolerance of the food becomes more likely.

When asked why he thought people overestimated food allergy, Dr. Fiocchi said that "people like attributing adverse reactions and feelings to food. In the United States and Europe, many people go to alternative practitioners who use tests that measure the thoughts of people after eating different foods. They might attribute food allergies to symptoms such as depression, obesity, sexual disorders, and so on. There are all sorts of symptoms that cannot really be attributed to food allergies," he noted.

Dr. Bahna and Dr. Fiocchi have disclosed no relevant financial relationships.

World Allergy Organization (WAO) 2010 International Scientific Conference. Presented December 5, 2010.

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