Date Published: September 12, 2018
Publisher: BioMed Central
Author(s): Susan Waserman, Philippe Bégin, Wade Watson.
Food allergy is defined as an adverse immunologic response to a food protein. Food-related reactions are associated with a broad range of signs and symptoms that may involve any body system, including the skin, gastrointestinal and respiratory tracts, and cardiovascular system. Immunoglobulin E (IgE)-mediated food allergy is a leading cause of anaphylaxis and, therefore, referral to an allergist for timely and appropriate diagnosis and treatment is imperative. Diagnosis entails a careful history and diagnostic tests, such as skin prick tests, serum-specific IgE and, if indicated, an oral food challenge. Once the diagnosis of food allergy is confirmed, strict elimination of the offending food allergen from the diet is generally necessary; however, in the case of cow’s milk and egg allergy, many allergic children are able to eat these foods in their baked form. This article provides an overview of the epidemiology, pathophysiology, diagnosis, and management of IgE-mediated food allergy.
IgE-mediated food allergy is a leading cause of anaphylaxis, a severe, potentially fatal allergic reaction presenting to emergency departments  (see article on Anaphylaxis in this supplement). A recent survey of over 5700 Canadian households (15,022 individuals) estimated the prevalence of food allergy in Canada to be 7.5% (self-reported; Table 1) . Annually, approximately 200 deaths in the United States are attributed to food allergy . A review of anaphylaxis deaths that occurred between 1986 and 2011 in Ontario, Canada, attributed 48% of these deaths to food allergy . When comparing the time periods 1986–1998 and 1999–2011, fatalities due to food allergy declined from 28 to 12 cases, whereas fatalities due to medications and unknown causes increased (from 6 to 10 and from 1 to 5, respectively).Table 1Prevalence (self-reported, unadjusted) estimates for probable food allergy in Canada Food allergenPrevalence (%)ChildrenAdultsPeanut2.20.6Tree nuts1.51.0Fish0.90.5Shellfish0.81.6Sesame0.10.2Milk0.20.2Egg1.00.5Wheat0.20.2Soy0.10.1
The term food allergy is used to describe an adverse immunologic response to a food protein. It is important to distinguish food allergy from other non-immune-mediated adverse reactions to foods, particularly since more than 20% of adults and children alter their diets due to perceived food allergy . Adverse reactions that are not classified as food allergy include food intolerances secondary to metabolic disorders (e.g., lactose intolerance), reactions to toxic contaminants (e.g., bacteria in decomposing scombroid fish will convert histidine, an amino acid, to histamine) or pharmacologically active food components (e.g., caffeine in coffee causing jitteriness, tyramine in aged cheeses triggering migraine).
Although food allergy can arise to any food, Health Canada has identified the following 10 priority allergens: cow’s milk (CM), egg, peanut, tree nuts, fish/shellfish, wheat, sesame seed, soy, mustard and sulphites (a food additive) . Canadian food labeling regulations require food manufacturers to list these food allergens, gluten sources and added sulphites on food labels.
The natural history of food allergy varies by type of food allergen. CM and egg allergy can present in the 1st year of life, and although some children may outgrow these allergies by early school age, others may not develop tolerance until their teenage years. Studies have reported that 19% of subjects achieve tolerance to CM by age 4 years, 42% by age 8 years, 64% by age 12 years, and 79% by 16 years . For egg allergy, 4% achieve tolerance by age 4 years, 12% by age 6 years, 37% by age 10 years, and 68% by age 16 years . In contrast, allergy to peanut, tree nuts, fish, and shellfish are generally lifelong, although 20% of individuals may outgrow peanut allergy . Peanut and tree nuts are responsible for the most serious allergic reactions and food-allergy related fatalities [15, 16].
Food-related reactions are associated with a broad range of signs and symptoms that may involve any body system, including the skin, GI and respiratory tracts, and cardiovascular system (Table 2). Food allergy is not felt to play a role in chronic respiratory symptoms.Table 2Signs and symptoms of food allergyIgE-mediated (immediate reactions)Non-IgE-mediated (delayed/chronic reactions)Skin Urticaria√ Angioedema√ Erythema√√ Pruritus√√ Eczematous rash/lesions√√Respiratory Laryngeal edema√ Rhinorrhea√ Bronchospasm√ Nasal congestion√ Cough√ Chest tightness√ Wheezing√ Dyspnea√Gastrointestinal Angioedema of the lips, tongue, palate√ Oral pruritus√ Tongue swelling√ Vomiting√√ Diarrhea√√ Pain√√Cardiovascular Presyncope/syncope√ Hypotension√ Tachycardia√
The diagnosis of food allergy requires a detailed history and physical examination, as well as diagnostic tests such as skin prick tests (SPT) and/or food-specific serum IgE assessment. In some cases, an oral food challenge (OFC) may also be required [6, 8]. Referral to an allergist is important to confirm the diagnosis of a suspected food allergy. Patients should avoid the food in question until assessment, and an epinephrine auto-injector (EAI) should be prescribed, even if the diagnosis is uncertain .
A simplified algorithm for the diagnosis and management of food allergy is provided in Fig. 2.Fig. 2Simplified algorithm for the diagnosis and management of food allergy. IgE immunoglobulin E
The prognosis of food allergy is complex and dependent on the particular food. Although most infants and young children outgrow allergies to CM, egg, soy and wheat, there is evidence that an increasing number of children may not outgrow allergies to CM and egg until their teenage years [12, 13]. Children should be re-evaluated by their allergist at regular intervals to determine whether clinical tolerance has developed. In most cases, allergy to peanut, tree nuts, fish, and shellfish is lifelong.
IgE-mediated food allergy is an important clinical problem of increasing prevalence. Assessment by an allergist is essential for appropriate diagnosis and treatment. Diagnosis is based on a careful history and diagnostic tests, such as SPT, food-specific serum IgE testing (where appropriate) and, if indicated, OFCs. The mainstay of treatment is avoidance of the responsible food(s), and timely administration of epinephrine for allergic reactions. Current research on treatment is focused on food desensitization. Further insights into the pathophysiology of food allergy and anaphylaxis will lead to the development of improved methods for prevention, diagnosis, and management.
Food allergy is defined as an adverse immunologic response to a food protein.Referral to an allergist is important for appropriate diagnosis and treatment.Diagnosis of a food allergy requires a detailed history and diagnostic tests, such as SPT and/or food-specific serum IgE measurement; in some cases, OFCs may also be required.Management of food allergy involves avoidance of the responsible food(s) and injectable epinephrine.For patients with systemic symptoms, the treatment of choice is epinephrine administered by intramuscular injection into the lateral thigh.Data suggests that it may take longer to “outgrow” allergies to CM and egg than previously reported. Allergy to peanut, tree nuts, fish, and shellfish is usually life-long.