Egg allergy
Egg allergy is an immune hypersensitivity to proteins found in chicken eggs, and possibly goose, duck, or turkey eggs.[2] Symptoms can be either rapid or gradual in onset. The latter can take hours to days to appear. The former may include anaphylaxis, a potentially life-threatening condition which requires treatment with epinephrine. Other presentations may include atopic dermatitis or inflammation of the esophagus.[2][10]
Egg allergy
Consumption of chicken eggs, and also of baked goods that have eggs in the recipe.[2]
Medical history and standard allergy tests[3]
Introduction to allergenic foods during infancy[4]
Less than 30% of childhood egg allergies will persist into adulthood.[8]
In developed countries the prevalence of egg allergy in children under the age of five years is 1.8-2.0%.[9]
In the United States, 90% of allergic responses to foods are caused by cow's milk, eggs, wheat, shellfish, peanuts, tree nuts, fish, and soybeans.[11] The declaration of the presence of trace amounts of allergens in foods is not mandatory in any country, with the exception of Brazil.[12][13][14]
Prevention is by avoiding eating eggs and foods that may contain eggs, such as cake or cookies.[2] It is unclear if the early introduction of the eggs to the diet of babies aged 4–6 months decreases the risk of egg allergies.[15][16][17][18]
Egg allergy appears mainly in children but can persist into adulthood. In the United States, it is the second most common food allergy in children after cow's milk. Most children outgrow egg allergy by the age of five, but some people remain allergic for a lifetime.[19][20] In North America and Western Europe, egg allergy occurs in 0.5% to 2.5% of children under the age of five years.[2][9] The majority grow out of it by school age, but for roughly one-third, the allergy persists into adulthood. Strong predictors for adult-persistence are anaphylaxis, high egg-specific serum immunoglobulin E (IgE), robust response to the skin prick test and absence of tolerance to egg-containing baked foods.[2][8]
Causes[edit]
Eating egg[edit]
The cause is typically the eating of eggs or foods that contain eggs. Briefly, the immune system over-reacts to proteins found in eggs. This allergic reaction may be triggered by small amounts of egg, even egg incorporated into cooked foods, such as cake. People with an allergy to chicken eggs may also be reactive to goose, duck, or turkey eggs.[2]
Vaccines[edit]
Influenza vaccines are created by injecting a live virus into fertilized chicken eggs.[23] The viruses are harvested, killed and purified, but a residual amount of egg white protein remains. For adults ages 18 and older there is an option to receive recombinant flu vaccines (RIV3 or RIV4) which are grown on mammalian cell cultures instead of in eggs, and so are no risk for people with severe egg allergy.[24] Recommendations are that for people with a history of mild egg allergy should receive any IIV or RIV vaccine. People with a more severe allergic reaction may also receive any IIV or RIV, but in an inpatient or outpatient medical setting, administered by a healthcare provider. People with a known severe allergic reaction to influenza vaccine (which could be egg protein or the gelatin or the neomycin components of the vaccine) should not receive a flu vaccine.[24]
Each year the American Academy of Pediatrics (AAP) publishes recommendations for prevention and control of influenza in children.[25][26][27] In the 2016-2017 guidelines a change was made, that children with a history of egg allergy may receive the IIV3 or IIV4 vaccine without special precautions. It did, however, state that "Standard vaccination practice should include the ability to respond to acute hypersensitivity reactions."[25] Prior to this, AAP recommended precautions based on egg allergy history: if no history, immunize; if a history of mild reaction, i.e., hives, immunize in a medical setting with healthcare professionals and resuscitative equipment available; if a history of severe reactions, refer to an allergist.[26][27]
The measles and mumps parts of the "MMR vaccine" (for measles, mumps, and rubella) are cultured on chick embryo cell culture and contain trace amounts of egg protein. The amount of egg protein is lower than in influenza vaccines and the risk of an allergic reaction is much lower.[28] One guideline stated that all infants and children should get the two MMR vaccinations, mentioning that "Studies on large numbers of egg-allergic children show there is no increased risk of severe allergic reactions to the vaccines."[29] Another guideline recommended that if a child has a known medical history of severe anaphylaxis reaction to eggs, then the vaccination should be done in a hospital center, and the child be kept for observation for 60 minutes before being allowed to leave.[28] The second guideline also stated that if there was a severe reaction to the first vaccination - which could have been to egg protein or the gelatin and neomycin components of the vaccine - the second is contraindicated.[28]
Exercise as a contributing factor[edit]
There is a condition called food-dependent, exercise-induced anaphylaxis (FDEIAn). Exercise can trigger hives and more severe symptoms of an allergic reaction. For some people with this condition, exercise alone is not sufficient, nor consumption of a food to which they are mildly allergic sufficient, but when the food in question is consumed within a few hours before high intensity exercise, the result can be anaphylaxis. Egg are specifically mentioned as a causative food.[30][31][32] One theory is that exercise is stimulating the release of mediators such as histamine from IgE-activated mast cells.[32] Two of the reviews postulate that exercise is not essential for the development of symptoms, but rather that it is one of several augmentation factors, citing evidence that the culprit food in combination with alcohol or aspirin will result in a respiratory anaphylactic reaction.[30][32]
Diagnosis[edit]
Diagnosis of egg allergy is based on the person's history of allergic reactions, skin prick test (SPT), patch test and measurement of egg-specific serum immunoglobulin E (IgE or sIgE). Confirmation is by double-blind, placebo-controlled food challenges.[9][8] SPT and sIgE have sensitivity greater than 90% but specificity in the 50-60% range, meaning these tests will detect an egg sensitivity, but will also be positive for other allergens.[43] For young children, attempts have been made to identify SPT and sIgE responses strong enough to avoid the need for a confirming oral food challenge.[44]
Prevention[edit]
When eggs are introduced to a baby's diet is thought to affect risk of developing allergy, but there are contradictory recommendations. A 2016 review acknowledged that introducing peanuts early appears to have a benefit, but stated "The effect of early introduction of egg on egg allergy are controversial."[16] A meta-analysis published the same year supported the theory that early introduction of eggs into an infant's diet lowers risk,[15] and a review of allergens in general stated that introducing solid foods at 4–6 months may result in the lowest subsequent allergy risk.[17] However, an older consensus document from the American College of Allergy, Asthma and Immunology recommended that introduction of chicken eggs be delayed to 24 months of age.[18]
Prognosis[edit]
The majority of children outgrow egg allergy. One review reported that 70% of children will outgrow this allergy by 16 years.[8] In subsequently published longitudinal studies, one reported that for 140 infants who had challenge-confirmed egg allergy, 44% had resolved by two years.[52] A second reported that for 203 infants with confirmed IgE-mediated egg allergy, 45% resolved by two years of age, 66% by four years, and 71% by six years.[53] Children will be able to tolerate eggs as an ingredient in baked goods and well-cooked eggs sooner than under-cooked eggs.[8] Resolution was more likely if baseline serum IgE was lower, and if the baseline symptoms did not include anaphylaxis.[8][53]
Epidemiology[edit]
In countries in North America and western Europe, where use of cow's milk based infant formula is common, chicken egg allergy is the second most common food allergy in infants and young children after cow's milk.[9][8][54] However, in Japan, egg allergy is first and cow's milk second, followed by wheat and then the other common allergenic foods.[19] A review from South Africa reported egg and peanut as the two most common allergenic foods.[55]
Incidence and prevalence are terms commonly used in describing disease epidemiology. Incidence is newly diagnosed cases, which can be expressed as new cases per year per million people. Prevalence is the number of cases alive, expressible as existing cases per million people during a period of time.[56] Egg allergies are usually observed in infants and young children, and often disappear with age (see Prognosis), so prevalence of egg allergy may be expressed as a percentage of children under a set age. One review estimates that in North American and western European populations the prevalence of egg allergy in children under the age of five years is 1.8-2.0%.[9] A second described the range in young children as 0.5-2.5%.[2] Although the majority of children develop tolerance as they age into school age years, for roughly one-third the allergy persists into adulthood. Strong predictors for adult-persistent allergy are anaphylactic symptoms as a child, high egg-specific serum IgE, robust response to the skin prick test and absence of tolerance to egg-containing baked foods.[2][8] Self-reported allergy prevalence is always higher than food-challenge confirmed allergy.
For all age groups, a review of fifty studies conducted in Europe estimated 2.5% for self-reported egg allergy and 0.2% for confirmed.[54] National survey data in the United States collected in 2005 and 2006 showed that from age six and older, the prevalence of serum IgE confirmed egg allergy was under 0.2%.[57]
Adult-onset of egg allergy is rare, but there is confirmation of cases. Some were described as having started in late teenage years; another group were workers in the baking industry who were exposed to powdered egg dust.[58]
Society and culture[edit]
Food fear has a significant impact on quality of life.[61][62] For children with allergies, their quality of life is also affected by actions of their peers. There is an increased occurrence of bullying, which can include threats or acts of deliberately being touched with foods they need to avoid, also having their allergen-free food deliberately contaminated.[81]