Food Allergy Articles

Periodically, we provide short articles on various food allergy topics and discussion in the food allergy community:

Be Prepared to Treat an Allergic Reaction 

1. Have your child’s doctor complete a Food Allergy Action Plan (FAAP), providing clear instructions on how to treat an allergic reaction, and distribute copies to school officials. A blank FAAP is available for download in English and seven other languages here. 

2. Instruct school staff to follow your child’s FAAP immediately – not to call you to assess the situation. The FAAP provides school staff members with information to quickly evaluate and treat an allergic reaction.

3. Teach all those who care for your child not to hesitate to use an epinephrine auto-injector, such as EpiPen® or Twinject®. Studies show that the sooner epinephrine is administered during an anaphylactic reaction, the better the outcome will be. EpiPen® or Twinject® trainers, auto-injector devices that do not have a needle or medication in them, are available through FAAN to help you and others practice using an epinephrine auto-injector.

4. Meet with local emergency medical technicians so that you know what to expect when you call them in an emergency.

Adapted from Food Allergy News, Vol. 14, No. 3.

 

Food Allergy Testing: When, Why, and What Does It Mean?

by Hugh A. Sampson, M.D.

When evaluating for food allergy or other allergic problems, it is not uncommon for an allergist to test for foods that a patient has never knowingly eaten or is eating without obvious problems. This is especially true in children with moderate to severe atopic dermatitis (eczema) or asthma, where acute symptoms may not be readily apparent following eating, or in children with a known food allergy.

For example, infants with milk or egg allergy develop other food allergies in about 35% of cases, and children with peanut allergy will develop allergy to at least one tree nut in about one-third of cases.

Negative tests are very reassuring that the food can be ingested safely, except in allergic disorders that are not due to IgE (allergic) antibodies, such as certain types of food allergies that cause symptoms limited to the gut (abdominal pain, vomiting, and diarrhea). The problem arises when a child tests positive to a food that he or she is eating with no apparent problem.

Although no diagnostic test in medicine is 100% accurate, nowhere does the discrepancy between a positive laboratory test and the absence of clinical symptoms seem more apparent than in the various tests used to diagnose food allergy. In large part, this stems from a misinterpretation or “over-interpretation” of what the test can actually do.

A positive prick skin test to egg or milk simply indicates that a person has IgE antibodies to milk or egg — that the patient is “sensitized” to milk or egg. The positive prick skin test does not necessarily mean that the patient will experience an allergic reaction to milk or egg.

Overall, less than one-half of individuals with a positive skin test to a food will develop allergic symptoms if they eat that food. The larger the skin test wheal (raised area), the more likely it is that someone will react to the food, but no skin test size is 100 percent definitive.

Many Factors
When determining whether someone is likely to react to a food, the allergist must weigh a number of factors, including a detailed history, prick skin test results, and food-specific IgE antibody levels. Even after considering all these factors, the allergist may still not know whether a patient will react to a specific food, and a food challenge may be recommended.

Many parents wonder how their children can have positive skin tests or blood tests to foods that they have never eaten, since you cannot make IgE antibodies against something that your immune system has never seen.

Because many foods are made up of related proteins (i.e., botanically related, such as legumes — peanuts, peas, green beans, lentils, etc.), the skin test or blood test may not fully discriminate between various members of food families. Consequently many of the tests will appear to be positive, even though the patient will not react to the food when it is eaten.

Cross Reactivity
The tendency for IgE antibodies to bind to several different related foods is called “cross reactivity.” About 90 percent of peanut-allergic patients can ingest all other members of the legume family (peas, beans, soy, lentil, chickpeas) without allergic symptoms, even though they may have positive skin tests to many of these foods. About 90% of milk- or egg-allergic patients can eat beef or chicken, respectively, even though their skin tests are frequently positive to both.

Grass pollen-allergic patients often test positive to grains such as wheat, oat, and corn, but they almost always can eat those foods with no problem. Certain pollen proteins are similar to food proteins (such as ragweed pollen and melons and bananas or birch pollen and apple, plum, carrot, kiwi, etc.). Consequently, birch pollen allergic (“spring hay fever” or allergic rhinitis) or ragweed-allergic (“fall hay fever”) patients may have positive allergy tests to related foods and not experience any symptoms when the food is eaten.

In addition, it is possible that infants become exposed to food proteins from inevitable and unsuspected places in our environment. Researchers have suggested a number of possibilities: processed foods contaminated with other foods, inhalation of food protein in vapor particles from cooking or in house dust, small amounts of food proteins passed in breast milk, residual food on parents’ or siblings’ hands contacting the skin of babies with eczema, and possibly by contact with food protein in the mother before the child is born.

As noted above, many of these exposures are inevitable, and researchers cannot agree whether some of these exposures — for example, food protein in breast milk or the mother’s system prior to birth — may be protective, rather than harmful.

Tests
Another type of antibody, IgG, is typically made by the immune system to help protect us from infection; however, IgG antibodies also are made against the foods we eat and are normally found in most individuals. Levels of food-specific IgG antibodies may be higher in some individuals who have various gastrointestinal disorders, but this does not necessarily signify an allergy to the specific food.

A variety of other tests are used to “diagnose” food allergy, but at this point, they must be considered “unproven” until well-controlled clinical trials demonstrate their value in identifying specific food allergies.

Although certain allergy tests are very accurate at detecting and quantifying IgE (allergic) antibodies, they must be interpreted by someone who is highly skilled in the diagnosis of food allergy and who understands the clinical limitations of these tests.

Over the past decade, research has enabled the allergist to diagnose more accurately which patients will actually react to a food and when they have likely “outgrown” their food allergy, but in many cases, the physician-supervised food challenge is still necessary to provide the patient with the correct diagnosis.

Positive skin tests or blood tests to a food that someone is eating regularly with no allergic symptoms, including chronic eczema, hives, or asthma, are never a good reason to eliminate the food from the diet. Only by considering the patient’s history and allergy test results can the physician decide what foods should be removed from a patient’s diet.

Hugh A. Sampson, M.D., is professor of pediatrics and head of the Jaffe Food Allergy Institute at Mount Sinai Medical Center in New York City. He is also director of FAAN’s Medical Advisory Board.

Adapted from Food Allergy News, February-March 2006.

 

Are Food Allergies on the Rise?

by Vaishali S. Mankad, M.D. and A. Wesley Burks, M.D.

Food allergy affects up to 6% of young children and 3.5% of adults in the United States. In contrast to 30 or 40 years ago, it is not uncommon to know a family member, neighbor, or friend affected by a food allergy. There has been a growing concern that this phenomenon represents an increase in the prevalence of food allergies rather than a greater public awareness or better media coverage of the problem.

Based on large-scale population studies, there is good evidence that allergic diseases such as allergic rhinitis (hay fever), asthma, and atopic dermatitis (eczema) have increased in the last few decades.

Evidence is now mounting that there is a rise in the occurrence of food allergies that appears to parallel the rise in other allergic diseases. Direct evidence for the increase in food allergies comes from two studies that focus specifically on peanut allergy.

In one study, Jane Grundy of The David Hide Asthma and Allergy Research Centre and her colleagues looked at groups of children aged three to four, born at two different time periods on the Isle of Wight in England. There were over 1,000 participants in each group. Parents of these children completed questionnaires about symptoms of allergic diseases, including food allergy. Children also had allergy skin tests performed.

Those with positive skin tests to peanuts who had not had a convincing allergic reaction to peanut, or who had never eaten peanut, were offered food challenges to confirm peanut allergy.

The investigators found that the number of children with reported peanut allergy (by questionnaire) had doubled from 0.5%  to 1% over the five-year time period. The proportion of children with positive skin tests to peanut had increased threefold from 1.1% to 3.3%. In children with positive skin tests, the overall estimate of true peanut allergy was 1.5% when adding up those with convincing clinical reactions and positive food challenges.

In the United States, Dr. Scott Sicherer and colleagues, using a nationwide telephone survey with over 10,000 participants, found that the rate of peanut allergy doubled in children from 0.6% to 1.2% over a five-year period.

What is surprising is that only three-quarters of the children and less than half of the adults in this study sought a medical evaluation of the allergy despite reporting severe reactions and multiple reactions during their lifetime.

Of those who did seek medical evaluation, fewer than half received a prescription for self-injectable epinephrine. We still are awaiting studies to be performed regarding the possible increase in prevalence of other common food allergens.

Why are food allergies on the rise?
Several theories have been put forth to attempt to explain the rise in food allergies. One leading theory is the “Hygiene Hypothesis,” first proposed by British researcher Dr. David Strachan in 1989.

This theory states that exposure to certain germs and infections early in life are important in training the immune system to do what it is intended to do— recognize foreign threats to the body. The Western lifestyle of cleanliness and obsession with hygiene has skewed the immune system toward the development of allergic diseases.

Studies done in Europe found that children raised on farms and rural areas, where there was exposure to bacteria from animals, had fewer allergic diseases compared with those living in cities.

Similarly, children who attend childcare or who have older siblings, thus having greater exposure to infections, have a decreased incidence of asthma and wheezing.

Another explanation for the rise in food allergy is introduction of foods too early in an infant’s diet, before the immune system is mature enough to handle them. This could occur through breastfeeding or an unintended exposure to highly processed foods in the Western diet that may contain hidden sources of the allergens.

Cooking practices can also affect the development of food allergies. For example, roasting a peanut enhances its allergenic potential compared to other forms of preparing peanut. Peanut allergy is more common in the U.S. where peanuts are roasted, as compared to China where peanuts are boiled.

What is on the horizon for management and prevention of food allergies?
New treatments of food allergy are emerging. These include procedures for desensitization that change the way the immune system responds to allergens, much in the same way allergy shots work for hayfever.

There are ongoing studies to attempt allergy desensitization by the injection of peanut protein that has been modified to prevent an allergic reaction but is still recognized by the immune system as the food protein. Studies are also ongoing to attempt desensitization by the oral route, where different immune mechanisms are likely at play.

The question remains whether we can combat the rise in food allergies by preventing the occurrence of food allergies in the first place. These include studies with maternal avoidance of common allergy-causing foods during pregnancy and while breastfeeding, and delaying introduction of solid food in an infant’s diet. Unfortunately, many of these studies have yielded conflicting results that do not allow us to make definite recommendations other than delaying introduction of solid foods until six months of age.

Nevertheless, the rise in food allergies has created an urgency to understand what makes some foods allergenic and to identify the risk factors of developing food allergies in order to define better strategies for prevention.

Vaishali S. Mankad, M.D., is Clinical Associate at the Division of Pediatric Allergy and Immunology, Duke University Medical Center, Durham, NC.

Wesley Burks, M.D., is Chief, Division of Pediatric Allergy and Immunology, Department of Pediatrics, Duke University Medical Center, Durham, NC. He is also a member of FAAN’s Medical Advisory Board.


Adapted from Food Allergy News, October – November 2006.

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