Food allergy is defined as an immune-mediated adverse health reaction that occurs reproducibly on exposure to a given food. More than 12 million people in the United States have food allergies, which account for 30,000 emergency department visits and more than 100 deaths annually.
Food allergy (FA) is estimated to affect approximately 5% of children, teens, and adults. Specifically, peanut allergy occurs in approximately 0.6% of people, seafood allergy in 0.2%-0.5%, and milk and egg allergy in approximately 2%. Children with FA have an increased likelihood of asthma, atopic dermatitis, and respiratory allergies. Typically, FA is a reaction to a protein in the food that causes the body’s immune system to identify it as harmful. An allergen-specific, IgE-mediated FA requires both the presence of clinical symptoms and sensitization on exposure to a given food item.
Risk Factors
Patients with a medical history of asthma, atopic dermatitis, eosinophilic esophagitis, and exercise-induced anaphylaxis have an increased associated risk for FA. Symptoms often manifest within the first 2 years of life but can occur at any time.
Clinical Manifestations
The clinical manifestations of FA can involve multiple organ systems:
– Gastrointestinal: The most common gastrointestinal reaction is vomiting from an immediate GI hypersensitivity to a given food.
– Cutaneous: The most common cutaneous manifestations include hives during acute urticaria. Soft-tissue swelling from angioedema occurs less commonly. Atopic dermatitis and allergic contact dermatitis can be exacerbated.
– Respiratory: Respiratory reactions are rare but can occur in conjunction with other systemic manifestations.
Diagnosis
A diagnosis of FA should be considered in patients who present with an allergic reaction shortly after eating; in addition, FA may be considered in children with moderate to severe atopic dermatitis. A careful history usually provides the clues that a reaction may be allergic in nature, and physical exam may or may not show the manifestations of an allergic reaction at the time of the evaluation.
By Dr. Neil S.Skolnik and Dr. Sona M. Garg
Parent and patient reports should be confirmed with further testing, as 50%-90% of presumed FAs turn out to be untrue. Confirmation may involve oral food challenge tests or tests of allergic sensitization. The panel recommends oral food challenge as the most accurate test, and it should be considered when diagnosing FA.
Skin prick tests (SPTs) can be helpful, as they are sensitive both for FA and have high negative predictive value. SPTs, however, have low specificity and are prone to false positive results, with many people who do not manifest FA still having a positive reaction to a food.
Allergen-specific serum IgE is helpful in identifying foods that provoke IgE-mediated FA, and it has similar accuracy to SPTs. Food elimination diets can help diagnose non-IgE-mediated FA when symptoms resolve and do not recur on exclusion of a given food. All other tests suffer from lack of specificity and may cause patients to make substantial efforts to avoid foods that may pose no danger. Intradermal tests, measurement of total serum IgE, and atopy patch tests are not recommended.
Natural History
Most children with FA will eventually tolerate milk, egg, soy, and wheat, though fewer will eventually be able to tolerate tree nuts and peanuts. Resolution of FAs in children often occurs during the teenage years. The higher the level of serum IgE, the less likely it is that the FA will resolve. A decrease in IgE levels often is associated with the ability to tolerate the food. FAs that begin in adulthood often do not resolve.
Treatment
Allergen avoidance is the mainstay of prevention and treatment. The challenge is deciding whether potentially cross-reactive foods also need to be avoided.
Patients and families need to learn how to accurately read food labels. By law, eight major food allergens (milk, egg, peanut, tree nuts, soy, wheat, fish, and crustacean shellfish) that are responsible for more than 90% of serious adverse food-induced reactions must be included on food labels when appropriate.
Currently, there are no medications recommended for prevention of IgE-mediated food allergies.
When a patient has a FA reaction, antihistamines on an as-needed basis are the recommended treatment. In severe cases, such as anaphylaxis, patients should be treated immediately with an intramuscular dose of epinephrine. Secondary treatment will depend on the patient’s response and can involve hemodynamic support and/or adjunctive treatment with albuterol, diphenhydramine, H2-blockers, and corticosteroids.
Vaccination
A National Institute of Allergy and Infectious Diseases expert panel recommended that children with egg allergies receive the measles/mumps/rubella and varicella (MMRV) vaccines even if they have had a severe allergic reaction to eggs. There is insufficient evidence regarding influenza vaccination of patients with a history of severe egg allergy. Yellow fever and rabies vaccines should not be administered to patients with severe egg allergies.