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Food Allergy abstract

clinical practice

N Engl J Med 2008;359:1252-60

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Diagnostic Algorithm for Egg Allergy

This treatment algorithm can be used for other food allergies if the test result associated with a positive predictive value (PPV) of 95% or higher is known for the population and if the likelihood ratio is known for a given test result. A double-blind, placebo-controlled food challenge should not be performed if the patient has a history of severe anaphylaxis. In the skin-prick test, the mean wheal diameter obtained depends in part on the age of the patient, the extract used, the method of performing the test, and the site on the body where the test is performed. Values for specific types of tree nuts have not been validated.

Management

Short-Term Management

Anaphylactic reactions require prompt treatment of symptoms with rapid-acting antihistamines and intramuscular epinephrine; frequently, inhaled beta-agonists and systemic corticosteroids are required. Patients should be immediately transported to the hospital, and oxygen and intravenous fluid support should be given (Fig. 2 in the Supplementary Appendix).

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Intramuscular epinephrine should be administered within minutes after the allergic reaction. The lateral thigh is the optimal route of administration. Subcutaneous or inhaled epinephrine provides suboptimal therapeutic levels of the drug.

Delayed use of epinephrine is associated with the risk of a fatal reaction and an increase in biphasic reactions (i.e., reactions in which delayed symptoms follow the early acute symptoms) due either to delayed absorption of allergens through the gastrointestinal tract or to a late-phase allergic response. Biphasic reactions are reported to occur in 6% of cases of anaphylaxis; half of these reactions are severe, and 90% occur within 4 to 12 hours after the first signs. Therefore, patients who have severe reactions requiring epinephrine should be monitored in the hospital. It is commonly recommended that patients presenting with respiratory symptoms be monitored closely for at least 8 hours, since most biphasic reactions occur within that period. Patients presenting with hypotension or loss of consciousness should be monitored for at least 24 hours. The use of oral prednisone (at a dose of 1 to 2 mg per kilogram of body weight per day for 3 days) is recommended to prevent the late phase of the reaction.

Long-Term Management

The cornerstone of the management of food allergies is avoidance of the relevant food allergens. The management of multiple food allergies is more complex than the management of single food allergies; the greater the number of food allergies, the higher the likelihood of subsequent allergic reactions. Consultation with a trained dietitian is critical in developing a plan to avoid relevant food allergens and in preventing secondary dietary deficiencies with potentially adverse nutritional consequences, such as rickets, iron-deficiency anemia, and impaired growth in children and osteoporosis due to a dairy-free diet in adults.

A multidisciplinary approach involving specialist physicians, nurses, and dietitians has been shown to markedly improve patient and family knowledge of the management of allergic reactions to food, and it has been associated with a reduction in the number of subsequent allergic reactions. Even with careful dietary advice, patients have reactions on average every 3 years; family members and other caretakers should be trained to recognize early symptoms of food allergy and to administer the necessary medications if an allergic reaction occurs. Medications for the treatment of anaphylaxis should be kept readily available. On the basis of clinical experience, it is recommended that these medications should include a rapidly acting antihistamine and - especially in all patients with a history of severe reactions or asthma - a device for self-injection of epinephrine. All patients with food allergy and coexisting asthma should have an inhaled bronchodilator. European guidelines also recommend the use of glucocorticoids in patients who have required epinephrine or have had bronchospasm (Table 1 in the Supplementary Appendix).

Given the frequent coexistence of multiple allergic diseases, children with egg allergy should be tested for other food allergies and evaluated for other atopic diseases, and those presenting with moderate-to-severe eczema at a young age should undergo testing for food allergies. The identification of other allergies will minimize the risk of a subsequent severe allergic reaction. Moreover, the management of one allergic disease may improve the outcome of other allergic diseases. For example, some studies have shown improvement of childhood eczema after the elimination of egg and other food allergens, although the relative contribution of such a diet to management is unclear. In a review of elimination diets, the greatest amelioration in eczema was noted to be in children younger than 2 years of age in whom a specific diagnosis of food allergy had been confirmed. As noted above, given the risks of nutritional deficiencies, elimination diets should not be undertaken without a clear diagnosis of food allergy and supervision by a dietitian.

Immunization

Common vaccines that are cultured in egg fibroblasts may contain small amounts of egg-protein allergen, and immunization with these vaccines might cause anaphylaxis in children with egg allergies. Thus, the American Academy of Pediatrics recommends that influenza vaccines produced in egg cultures not be used in patients with severe systemic allergic reactions to egg. This group also recommends that before vaccination, children with egg allergy and asthma undergo skin-prick testing with any influenza vaccine containing egg. If either an epicutaneous or an intradermal skin test is positive, the vaccine should be administered in multiple, graded doses under supervision.Skin-prick testing is not required before measles-mumps-rubella (MMR) vaccination in children with egg allergy. Allergic reactions to the MMR vaccine appear to be due to other components of the vaccine, such as neomycin and gelatin.

Guidelines from Professional Societies

The American Academy of Allergy, Asthma and Immunology has issued recommendations for the management of food allergy (www.aaaai.org/members/resources/practice_guidelines/food_allergy.asp), and the European Academy of Allergology and Clinical Immunology has issued recommendations for the management of anaphylaxis. The recommendations provided here are generally consistent with those guidelines.

Conclusions and Recommendations

The child in the vignette has egg allergy and associated conditions, and he requires management of his food allergy and other allergic disorders. The diagnosis of egg allergy should be made on the basis of a detailed history, skin-prick testing, specific IgE tests, and, if necessary, a food challenge in a medically supervised setting. Management should involve education and the prescription of supplies for the treatment of anaphylaxis. This treatment includes a short-acting antihistamine, self-injected intramuscular epinephrine, a beta-agonist inhaler with a spacer device, and - in Europe, although not routinely in the United States - oral corticosteroids. The child and his parents and caregivers should be educated in the use of these medications and should keep them readily available. He should wear a medical-alert bracelet detailing his food allergies. This bracelet should state that he carries epinephrine.

Involvement of a dietitian is warranted to assess the patient's nutritional status and to provide advice on foods that should be avoided and dietary supplements as needed. A history of egg allergy is not a contraindication to the MMR vaccine, but skin testing is recommended before administration of the influenza vaccine.

Children with a known food allergy should be routinely evaluated for other food allergies, with particular testing according to the patient's geographic location, since typical allergies vary among countries. Children should also be tested for sensitivity to inhalant allergens in order to minimize the risks of allergic reactions and asthma and other associated atopic disorders. Detailed strategies for the management of eczema, allergic rhinitis, and asthma are described elsewhere. Once adequate symptom control has been achieved, annual follow-up is recommended to assess children both for resolution of the egg allergy and for the emergence of coexisting allergic disorders.

Resources for patients with egg allergies include the American Academy of Allergy Asthma and Immunology (www.aaaai.org), the Food Allergy and Anaphylaxis Network (www.foodallergy.org), and the Anaphylaxis Campaign (www.anaphylaxis.org.uk).

Dr. Lack reports receiving consulting or lecture fees from Novartis, Synovate, Nutricia, ALK-Abelló, and Nestlé and serving as an expert witness for several medical cases involving food allergy. No other potential conflict of interest relevant to this article was reported.

I thank Drs. L.G. Du Toit, A.T. Fox, and S. Chan for critical review of an earlier version of the manuscript.

Source Information

From the Department of Paediatric Allergy, King's College London, and the Children's Allergy Service, Guy's and St. Thomas' National Health Service Foundation Trust - both in London.

An audio version of this article is available at www.nejm.org.

Address reprint requests to Dr. Lack at the Children's Allergy Service, 2nd Fl., South Wing, St. Thomas' Hospital, Westminster Bridge Rd., London SE1 7EH, United Kingdom, or at gideon.lack@kcl.ac.uk .