Current recommendations are to administer venom immunotherapy to individuals who have had a systemic life-threatening reaction from an insect sting and have positive venom skin tests or elevated levels of venom-specific IgE. All persons with a history of systemic reactions to insects should be instructed in the use of an epinephrine autoinjector and encouraged to wear a MedicAlert bracelet. Children younger than 16 years of age who have had only a cutaneous reaction generally do not require immunotherapy because their prognosis is benign and can be managed with the availability of epinephrine.
An adverse reaction to food is a generic description of anyuntoward reaction after food ingestion, including toxic reactions such as food poisoning and nontoxic reactions, which canbe subdivided further into nonimmune and immune reactions. Lactose intolerance is a nonimmune reaction. Food allergy orhypersensitivity reactions encompass immune reactions to foodand can be divided further into IgE-mediated reactions, whichare typically rapid in onset, and non-IgE-mediated reactions.
Oral tolerance is the process of suppression of the immune response to the array of dietary elements ingested daily. Food allergy or hypersensitivity reactions are the result of immune reactions to glycoproteins and develop in genetically predisposed individuals. In children, cow’s milk, eggs, peanuts, soybean, wheat, tree nuts, fish, and shellfish cause 90% of IgE-mediated reactions. In older children and adults, peanuts, tree nuts, fish, and shellfish account for most reactions. Exposure to the allergenic food protein results in cross-linking of the IgE receptor found on the mast cells and basophils, which become activated and degranulate, releasing numerous potent mediators and cytokines. Non-IgE-mediated reactions typically occur hours to days after the allergen ingestion and are manifest as gastrointestinal symptoms. A cell-mediated immune mechanism may be responsible.
Approximately 6% to 8% of children are affected with food allergy. In adults this declines to 1% to 2%.
Symptoms of hypersensitivity reactions vary from involvement of the skin, gastrointestinal tract, and respiratory tract to anaphylaxis. Non-IgE-mediated food allergy typically presents during infancy as proctitis/proctocolitis, enteropathy, or enterocolitis (Table 84-1).
In acute IgE reactions, skin prick allergy testing and serum testing to foods may help confirm the suspected food allergy.
A careful history focuses on symptoms, the time interval fromingestion to onset of symptoms, the quantity of food necessaryto evoke the reaction, the most recent reaction, patterns of reactivity, and associated factors such as exercise and medicationuse. Skin prick testing can be performed to confirm IgE-mediated food allergies. A negative skin test virtually excludes anIgE-mediated reaction (unless the clinical history suggests asevere reaction after an isolated ingestion of the food). A positive skin test indicates sensitization but does not prove clinicalreactivity and must be interpreted, based on the history.
Table 84-1 Gastrointestinal Food Allergic Disorders DISORDER AGE GROUP CHARACTERISTICS DIAGNOSIS PROGNOSIS/COURSE IgE-MEDIATED Acute gastrointestinal hypersensitivity Any Onset: minutes to 2 h Nausea, abdominal pain, emesis, History, positive PST, and/ or serum food-IgE Variable, food-dependent Milk, soy, egg, and wheat