Excerpt from Food Allergies

Please click here to view the full topic text: Food Allergies

Background

Adverse food reactions can be broadly classified into 2 categories. The first category consists of immunologically-mediated adverse reactions to foods; these reactions are unrelated to any physiologic effect of the food or food additive. These reactions include disorders mediated by immunoglobulin E (IgE) antibodies (eg, IgE-mediated reaction to peanuts), which begin during or soon after exposure to the food, and others resulting from non–IgE-mediated mechanisms (eg, non–IgE-mediated reactions such as protein-induced enterocolitis syndrome), which generally take several hours to evolve.  

The second category is food intolerance. These reactions include any adverse physiologic response to a food or food additive that is not immunologically mediated (eg, lactose intolerance, bacterial food poisoning).

Pathophysiology

Allergic reactions to food are IgE-mediated or non–IgE-mediated. Immune responses mediated by specific IgE antibodies are the most widely recognized mechanism of food hypersensitivity. Patients with atopy produce IgE antibodies to specific epitopes of the food allergen. These antibodies bind to high-affinity IgE receptors on circulating basophils and tissue mast cells present in the skin, gastrointestinal tract, and respiratory tract. Subsequent allergen exposure binds two adjacent IgE antibodies, resulting in receptor cross-linking and intracellular signaling that initiates the release of numerous mediators, including histamine, prostaglandins, leukotrienes, chemotactic factors, and cytokines. The effects of these mediators on surrounding tissues result in vasodilatation, smooth muscle contraction, and mucus secretion, which, in turn, are responsible for the spectrum of clinical symptoms observed during allergic reactions to food.

Food allergens are typically water-soluble glycoproteins resistant to heating and proteolysis with molecular weights of 10-70 kd. These characteristics facilitate the absorption of these allergens across mucosal surfaces. Numerous food allergens are purified and well-characterized, such as peanut Ara h1, Ara h2, and Ara h3; chicken egg white Gal d1, Gal d2, and Gal d3; soybean-Gly m1; fish-Gad c1; and shrimp-Pen a1. Closely related foods frequently contain allergens that cross-react immunologically (ie, lead to the generation of specific IgE antibodies detectable by skin prick or in vitro testing) but less frequently cross-react clinically. Finally, cross-reactive allergens have been identified among certain foods and airborne pollens (see Pollen-food allergy syndrome). Conserved homologous proteins shared by pollens and foods likely account for this cross-reactivity.

Frequency

United States

General surveys report that as many as 25-30% of households consider at least 1 family member to have a food allergy. This high rate is not supported by controlled studies in which food challenges are used to confirm patient histories. The actual prevalence of food allergies is estimated to be approximately 6% in infants and children and 3.7 % in adults. Several published prospective investigations have determined the prevalence of certain common food allergies in children (eg, cow milk, 2.5%; eggs, 1.3%; peanuts, 0.8%; wheat, 0.4%; soy, 0.4%).

International

Prospective studies from several different countries indicate that approximately 2.5% of newborn infants experience hypersensitivity reactions to cow milk in the first year of life. A hypersensitivity reaction to peanuts occurs in approximately 0.5% of children in the United Kingdom. Surveys from the United Kingdom indicate that 1.4-1.8% of adults experience adverse food reactions and 0.01-0.23% of adults are affected by adverse reactions to food additives. Studies from the Netherlands demonstrate that approximately 2% of the adult Dutch population is affected.

Mortality/Morbidity

• Severe anaphylactic reactions, including death, can occur following the ingestion of food. Typical symptoms observed in a food-induced anaphylactic reaction involve the skin, gastrointestinal tract, and respiratory tract. Frequently observed symptoms include oropharyngeal pruritus, angioedema (eg, laryngeal edema), stridor, dysphonia, cough, dyspnea, wheezing, nausea, vomiting, diarrhea, flushing, urticaria, and angioedema. Fatalities result from severe laryngeal edema, irreversible bronchospasm, refractory hypotension, or a combination thereof. Food allergy has been confirmed in approximately one third of the patients with anaphylaxis presenting to the emergency department at the Mayo Clinic.



• Peanuts, tree nuts, and shellfish are the foods most often implicated in severe food-induced anaphylactic reactions, although anaphylactic reactions have been reported to a wide variety of foods.



• Risk factors for fatal food-induced anaphylaxis include (1) the presence of asthma, especially in patients with poorly controlled disease; (2) previous episodes of anaphylaxis with the incriminated food; (3) a failure to recognize early symptoms of anaphylaxis; and (4) a delay or lack of immediate use of emergency medications (eg, epinephrine, antihistamines) to treat the allergic reaction.

Race

• No predilection is known.

Sex

• No predilection is known.

Age

• In infants and children younger than 3 years, the prevalence of food allergy is approximately 6%.



• The estimated prevalence in adults is approximately 3.7%.

Please click here to view the full topic text: Food Allergies