38.1 Food Allergy in a Nutshell

Food allergies are a growing health concern with a significant increase in reported prevalence. Allergic reactions to food can produce life-threatening anaphylaxis. Peanut allergy in particular is a significant public health problem. Peanut allergy often remains a life-long problem for many individuals, as less than 25% of peanut-allergic patients are expected to regain tolerance. Current recommendations for management include strict avoidance and a prescription for an auto-injectable form of epinephrine.

The increase in prevalence of peanut allergy occurred during a period of time when there was conflicting guidance regarding preventative measures for the development of peanut allergy. Before 2000, there were no guidelines regarding the timing for the introduction of peanut-containing products nor were there any purposeful strategies to delay the introduction of peanut-containing products to try to prevent the development of allergic disease. But in 2000, the American Academy of Pediatrics (AAP) recommended that “solid foods should not be introduced into the diet of high-risk infants until 6 months of age……and peanuts….until 3 years of age.” This recommendation was reversed in 2008. At that time, AAP recommended that “the introduction of solid foods not be delayed past 4–6 months of age.” However, they did not make any updated recommendations regarding the introduction of peanut-containing products.

The Learning Early About Peanut allergy (LEAP) study demonstrated that peanut-containing products can be safely introduced to high-risk infants between the ages of 4 and 11 months and that there is a monumental potential for peanut-allergy prevention. The National Institutes of Allergy and Infectious Diseases (NIAID) recently published an addendum guideline regarding the prevention of peanut allergy in the United States based on the findings from the LEAP study.

The NIAID-sponsored guidelines include the following three addendum recommendations:

1. 
   

   Infants with severe eczema, egg allergy, or both should have introduction of age-appropriate peanut-containing food as early as 4 to 6 months of age to reduce the risk of peanut allergy. The Expert Panel recommended to strongly consider evaluation by in vitro specific immunoglobulin E (IgE) testing and/or skin prick testing (SPT), and if necessary an oral food challenge. Then based on these results, introduce peanut-containing foods.

   
   
2. 
   

   Infants with mild-to-moderate eczema should have introduction of age-appropriate peanut-containing food around 6 months of age, in accordance with family preferences and cultural practices, to reduce the risk of peanut allergy. The Expert Panel recommended that infants in this category may have dietary peanut introduced at home without an in-office evaluation. The Expert Panel recognized that some caregivers and health care providers may desire an in-office supervised feeding and/or evaluation.

   
   
3. 
   

   Infants without eczema or any food allergy may have age-appropriate peanut-containing food freely introduced in their diet, together with other solid foods, and in accordance with family preferences and cultural practices.

There is an algorithm in the addendum guidelines to aid in assessing the high-risk infants in recommendation one. For these high-risk infants, it is recommended that they be evaluated and undergo skin testing by a specialist before the introduction of peanut-containing products. The Expert Panel did recognize that for those high-risk infants who do not have access to a specialist that testing for peanut-specific immunoglobulin E (sIgE) may be the preferred initial approach in certain instances.

The recommendations regarding when to introduce peanut-containing products into the diet have changed. New research demonstrated that early introduction of peanut-containing products around 4 to 6 months of age significantly reduced the risk of development of peanut allergy.

38.2 Definitions and Classification of Food Allergy

The first area of confusion when considering food allergy is its variable definition. A layperson may consider any adverse food reaction to be a “food allergy,” while an allergist regards only a reaction with an immunologic mechanism to be a true food allergy. The 2010 Guidelines recommend that the term food allergy be used to describe an adverse health effect arising from a specific immune response that occurs reproducibly upon exposure to a given food. The guidelines further define food as any substance which is intended for human consumption including food additives, drinks, chewing gum, and dietary supplements. Food allergens are identified as the specific components of food (typically proteins but sometimes also chemical haptens) that are recognized by allergen-specific immune cells and elicit specific immunologic reactions resulting in characteristic symptoms. Patients can develop sensitization to food allergens without having clinical allergy symptoms. To be clear, patients may have detectable allergen-specific IgE to food allergens without having any clinical manifestations upon exposure to those same foods. The guidelines emphasize that sensitization alone is not sufficient to define food allergy. Finally, patients can have reproducible adverse reactions to specific foods that do not have an immunologic mechanism; these nonimmunologic reactions are defined as food intolerances and should not be confused with food allergy.

Many adverse reactions to food occur which may mimic food allergy but for which there is no immunologic basis. Such adverse food reactions, or food intolerances, include host-specific metabolic disorders such as galactosemia, alcohol intolerance, and lactose intolerance. Patients may also have reactions to a pharmacologically active component in a food, such as caffeine or tyramine in aged cheese. Additionally, individuals may react to toxic contaminants in food such as the histaminic chemical in the spoiled dark meat of certain fish, resulting in scombroid poisoning.

It is conceptually helpful for the clinician to categorize the broad spectrum of food-induced allergic disorders based on their underlying immunopathology. These categories of food allergy include: IgE-mediated, non-IgE-mediated, mixed IgE- and non-IgE-mediated, and cell-mediated.

IgE-mediated reactions are characterized by a temporal relationship between the reaction and exposure to the food. Most typically, symptoms of IgE-mediated food allergy occur within minutes to hours of exposure to the food. In the vast majority of these patients, serum food-specific IgE antibodies can be measured which, in conjunction with typical signs and symptoms on exposure to the food in question, confirm the IgE-mediated pattern of reaction. Just as with inhalant allergy, the diagnosis of allergy requires the presence of a positive patient history along with a positive test of IgE. A positive test (either in vitro IgE or skin prick test) alone does not translate to clinically relevant allergy.

Non-IgE-mediated immunologic reactions occur in some gastrointestinal disorders, particularly in children; these reactions are thought to be induced by delayed, immune but not IgE-mediated reactions to specific foods. Examples of these non-IgE-mediated reactions include food protein-induced enterocolitis syndrome, food protein-induced enteropathy syndrome, and food protein-induced allergic proctocolitis syndrome.

Mixed IgE- and non-IgE-mediated mechanisms should be considered when symptoms typically involving the gastrointestinal tract are of a more chronic nature and are not closely related to ingestion of the food. These syndromes include the eosinophilic gastroenteropathies: eosinophilic gastroenteritis, eosinophilic esophagitis, and eosinophilic proctocolitis.

Finally, allergic-contact dermatitis is an example of a cell-mediated allergic mechanism. Allergic-contact dermatitis represents a cell-mediated allergic reaction to chemical haptens that are present in food, and may be seen in food handlers.

A clear understanding of these definitions and classification schemes is important as the clinician reads the medical literature, and more importantly, embarks upon evaluating the patient with possible food allergy. Familiarity with food allergy concepts is important for the otolaryngologist because many patients with upper airway inflammatory disease are atopic and are at increased risk for having concomitant food allergy. In order to provide comprehensive care of the allergic patient, some knowledge of basic definitions, categories of food allergy, and clinical manifestations, and facility with diagnostic testing and treatment strategies for food allergy are important.