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Overview

This Guidelines summary covers the management of egg allergy in adults and children.

Recommendations included in this summary: definition and mechanism; prevalence; risk factors; clinical presentation and severity; diagnosis; investigations; management; resolution of egg allergy; egg allergy in adults; other egg-related conditions; immunisation of egg-allergic children and adults; and psychological and social implications of egg allergy.

Recommendations not included in this summary: home introduction of egg; children with severe egg allergy; oral immunotherapy; management of egg allergy in nurseries and schools; and introduction of egg into the diet of infants from atopic families.

For a complete list of recommendations, refer to the full guideline.

This summary has been abridged for print. View the full summary online at guidelines.co.uk/456415.article  

Definition and mechanism

  • Egg allergy is an adverse immunological reaction, most often induced by the proteins in egg white, usually ovalbumin (Gal d 2) and/or ovomucoid (Gal d 1) mediated by egg-specific immunoglobulin E (IgE)
  • The production of egg-specific IgE is a prerequisite for developing type-1 hypersensitivity to egg. The route, timing, and dose of egg protein exposure, resulting in sensitisation and clinical allergy, are unknown
  • Late-phase and delayed hypersensitivity reactions also occur, typically in eczema.

Prevalence

  • The EuroPrevall birth cohort reports that challenge confirmed hen’s egg allergy, in children at 2 years of age, is about 1% across Europe and 2% in the UK
  • Egg allergy is much less common in adults. The prevalence of egg allergy in the adult population has been estimated at 0.1%
  • Newly diagnosed egg allergy in adults is rare.

Risk factors

  • Egg allergy in children is associated with eczema and rhinitis. Eczema is a significant risk factor for egg allergy
  • The onset of eczema predates egg allergy by an average of 3.5 months, and the likelihood of egg allergy increases with the severity of eczema. Boys with early-life eczema have the highest prevalence of egg sensitisation
  • Egg allergy is not associated with age of introduction of egg into the diet
  • Children who received antibiotics in the first week of life are more likely to develop egg allergy
  • Egg allergy may occur in association with other food allergies, such as cow’s milk, protein, or peanut.

Clinical presentation and severity

  • The onset of egg allergy is usually observed early in life, in children with eczema and atopy
  • Egg allergy most commonly presents after the first apparent ingestion. Most reactions occur to lightly cooked egg, with reactions to baked egg and raw egg being less common
  • Clinical reactions include urticaria and/or angio-oedema in 80–90% (within minutes) and gastrointestinal symptoms in 10–44% (within 2 hours)
  • Most reactions occurring in the community are mild, with facial erythema and/or urticaria
    • in children, a mild reaction is characterised by cutaneous symptoms on significant exposure (for example, a mouthful of cooked egg) sometimes associated with a single vomit
    • a hoarse cry, change in voice pitch, cough, stridor, or wheeze indicates involvement of the respiratory tract and a more severe reaction
    • occasionally, young children develop pallor and floppiness
  • Moderate-to-severe reactions with respiratory symptoms are less common; 5–10% in challenge studies, but less in the community where the initial triggering dose is usually lower. Prior to presentation to allergy services, anaphylaxis occurs in 7%
  • The severity of allergic reactions correlates with the amount of exposure; egg protein as determined by the amount of egg protein ingested and the degree of processing (baked in wheat, cooked or raw, cooking duration, and temperature)
    • baked egg as an ingredient in sponge cake would mostly cause a mild cutaneous reaction
    • skin contact to raw egg may induce local cutaneous reactions
    • systemic reactions have been reported when egg white has been applied to skin for the treatment of nappy rash
    • ingestion of raw or undercooked egg triggers more severe clinical reactions than well-cooked egg
  • In children with eczema who are allergic to egg protein, dietary exclusion of egg results in improvement of their eczema
  • Egg-allergic patients requiring referral to an allergy clinic are defined in Box 1. Note: early referral is beneficial, as a delay in baked egg introduction may limit the development of tolerance.

Box 1: Which patients with egg allergy should be referred to an allergy clinic?

  • History of moderate-to-severe reaction
  • Where there is diagnostic uncertainty
  • Egg allergy in association with other IgE-mediated food allergies
  • Severe eczema in children on an egg-containing diet
  • Allergy to baked egg that persists beyond the common age of resolution (6–7 years)
  • Adult-onset egg allergy
  • Egg allergy with requirement for yellow fever immunisation
  • Any child wishing to reintroduce egg but unable due to high anxiety
  • Egg-allergic patients on biologics and immunosuppressants.

Diagnosis

  • Acute clinical signs have usually resolved by the time the patient reaches medical attention. The clinical diagnosis is, therefore, made by a typical history of erythema, urticaria, angio-oedema, and/or vomiting with rapid onset (usually within minutes) after ingestion of egg
  • Children with a clear history of a mild reaction to egg can be diagnosed and managed in a primary care setting without further testing. Only children with moderate-to-severe reactions, or where the history remains unclear, require further investigation to confirm and manage egg allergy.

Investigations

Skin prick test

  • Skin prick testing (SPT) using commercially available standardised whole-egg reagent should only be carried out if there is clinical suspicion of egg allergy. SPT weal size does not correlate with clinical severity
  • Traditionally, cut-off levels for egg white SPT weal size of 3 mm or greater have been used to support a clinical diagnosis of egg allergy
  • Higher cut-off levels are associated with higher specificity and positive predictive values, for example, a SPT weal size of 5 mm to egg white is 100% diagnostic in a child under 2 years of age
  • Cut-off values for prick-to-prick testing with raw egg are reported as 13 mm or greater.

Egg-specific IgE

  • When skin prick testing is not available, measurement of egg-specific IgE may be carried out in patients with a history of moderate/severe reactions to egg-containing food, to confirm a clinical suspicion of egg allergy
  • Low levels of egg-specific IgE may be found in children without clinical egg allergy
  • The measurement of egg-specific IgE in the absence of a history of egg ingestion is discouraged as, in this circumstance, the test has poor specificity and low negative predictive value; cautious home introduction or oral challenge will subsequently be required if the egg-specific IgE level is positive but low
  • Measurement of peanut-specific IgE should be included in infants with moderate/severe egg allergy to guide peanut allergy prevention advice.

Egg component testing

  • The egg white components are ovomucoid (Gal d 1), ovalbumin (Gal d 2), ovotransferrin (Gal d 3), lysozyme (Gal d 4), and livetin (Gal d 5)
  • Persisting egg allergy is associated with a positive Gal d 1, and a level 11 kU/L or greater indicates a high risk of reacting to cooked and raw egg. Gal d 1 is also a good indicator of whether the child is allergic only to raw egg, or to both cooked and raw egg
  • The acquisition of tolerance to egg is associated with a decrease in IgE to egg white and Gal d 1
  • When using test results to identify children at a high risk of anaphylaxis, although egg white serum IgE levels are more sensitive, Gal d 1 has better positive predictive value and specificity
  • Egg components are rarely needed for the routine diagnosis and management of egg allergy in children, but can be a useful adjunct for the assessment of egg allergy resolution in adults.

Box 2: Making a diagnosis of egg allergy

  • Most children should receive a clinical diagnosis without resorting to food challenge
  • If the history is unclear, a negative SPT can exclude egg allergy
  • SPT weal size or level of specific IgE does not predict the severity of allergic reactions to egg
  • The severity of a reaction depends on the amount of allergen ingested, the matrix, how well it is cooked, concomitant asthma, exercise, and illness.

Management

Avoidance diets

  • Eggs served in a recognisable form are relatively easy to avoid. They are used as an ingredient of many manufactured foods; therefore, food labels must be consistently checked
  • Uncommon sources of egg include Quorn, confectionary, and egg hidden in a food that is usually ‘egg free’, for example, pizza dough
  • Extra care needs to be taken with foods sold loose (non-pre-packed) as there may be risk of cross-contamination
  • Individuals with severe egg allergy will need to completely avoid food sold loose/on buffets
  • All species of egg (for example, quail/duck) are given the generic name ‘egg’ on a label
  • Verbal and written advice on avoidance of egg products should be provided.

Allergen labelling

  • Egg must be emphasised in bold in the ingredient list
  • Other terms for egg include albumin, ovalbumin, globulin, ovoglobulin, livetin, ovomucin, vitellin, ovovitellin, lysozyme, and alpha-livetin. These are not allowed to be substituted for the term ‘egg’. Knowledge of these terms may be useful for detecting egg protein in non-EU products.

Breastfeeding and egg allergy

  • Most breastfeeding mothers with egg-allergic children should continue to breastfeed on an unrestricted diet
  • Egg protein from the maternal diet is detectable in breast milk and may cause reactions in a very small number of infants
  • A trial of maternal egg-free diet may be helpful in the following circumstances:
    1. infants with persistent eczema poorly responsive to treatment, where egg is a known or suspected trigger
    2. infants suspected to be reacting to maternal ingestion of egg
  • Strict maternal egg exclusion should be recommended for 4–6 weeks, followed by reintroduction to ensure unnecessary egg exclusion does not continue.

Cross-reactivity between eggs from hens and other bird species

  • Skin test reactivity to other avian eggs, especially quail and duck, is common in children with hen’s egg allergy
  • It is generally accepted that those avoiding hen’s egg should also avoid eggs from other avian species, such as duck, goose, and quail.

When to refer to a dietician

  • Although it may appear easy to take supplements or substitute other foods, many composite foods may contain eggs; adherence may be difficult without adversely affecting nutritional intake or quality of life
  • Whilst the exclusion of eggs does not necessarily lead to nutritional deficiency, a registered dietician should be involved if the diet is also compromised by the exclusion of other foods due to multiple food allergies, lifestyle, or religious reasons.

Provision of emergency medication and treatment plans

  • All families with egg-allergic children should have an appropriate oral antihistamine available, preferably a second-generation, non-drowsy antihistamine, to treat allergic reactions due to accidental ingestion
  • In practice, adrenaline autoinjectors are rarely required for children with egg allergy
  • The minority of children who have had severe reactions with evidence of airway narrowing (for example, wheeze, voice change, choking) or hypotension, should be provided with injectable adrenaline and their families reviewed annually by an allergy specialist
  • Children with egg allergy and asthma, requiring regular preventative treatment with inhaled corticosteroids, should also be considered for an adrenaline autoinjector
  • Families should receive training in how to use their emergency medication, including demonstration with a trainer device and provision of a management plan
  • Adults and young people with persisting egg allergy should be reassessed, especially prior to a move away from home, for example, to attend university, join the armed forces, or travel overseas. They should be provided with updated information about dietary management and the need for an adrenaline autoinjector reviewed.

Resolution of egg allergy

Prediction of resolution

  • At 1 year of age, complete resolution of egg allergy is more likely in children who can tolerate baked egg than those who continue to react
  • Children with mild/moderate egg allergy or with cutaneous reactions only are more likely to resolve
  • Persistence of egg allergy is associated with respiratory or multisystem symptoms, high egg-specific IgE, presence of other food allergies, or atopic comorbidities
  • Sensitisation to multiple egg allergen components (Gal d 1, Gal d 2, Gal d 3, or Gal d 5) may identify children at risk of persistent egg allergy.

Natural history of resolution

  • Egg allergy resolves spontaneously in many affected children over several years, whereas in adults it tends to persist
  • Allergy to well-cooked egg resolves in about one-third of children by 3 years of age, and two-thirds by 6 years of age. Egg allergy may continue until the teens
  • Tolerance to well-processed (baked or lightly cooked) egg occurs long before tolerance to uncooked egg
    • children who can tolerate baked egg may continue to react to lightly cooked egg. Children outgrow allergy to well-cooked egg approximately twice as quickly as they outgrow allergy to uncooked egg. Establishing the former is important to allow relaxation of dietary restrictions, and may help establish tolerance.

Reintroduction of egg into the diet

  • Most children with mild egg allergy tolerate gradual staged home introduction according to an egg ladder (see Figure 1 in the full guideline)
  • Baked egg introduction improves quality of life for egg-allergic children, enhances the natural development of tolerance, and de-restricts the diet
  • The speed with which egg allergy resolves varies between individuals, and therefore the timing and appropriateness of egg reintroduction should be individually assessed.

For recommendations on home introduction of egg, children with severe egg allergy, and oral immunotherapy, refer to the full guideline.

Egg allergy in adults

  • In contrast to egg allergy in children, egg allergy in adults is likely to be severe and long lasting. It is due to either persistent childhood egg allergy or to true adult-onset egg allergy, which is rare. Adults with persistence of childhood egg allergy have more sequential than conformational IgE epitopes of ovomucoid
  • Adult egg allergy may be:
    1. new onset adult egg allergy after eggs have been tolerated for years
    2. part of the bird-egg syndrome (a combination of bird-feather sensitisation and egg allergy) with an allergy to egg yolk. This syndrome is seen in subjects who are exposed to caged birds or pigeons. Typically, patients develop upper and lower respiratory symptoms on exposure to birds, and gastrointestinal symptoms with chicken meat or lightly-cooked eggs. Patients should receive egg avoidance advice, emergency medication, and be trained in its use
    3. occupational, for example, in workers from the baking industry, who develop sensitisation by inhalation
  • There is little information on the prognosis of adult egg allergy, and patients should be seen periodically to repeat specific IgE and to update training in the use of emergency medication
  • Older children or adults with a pre-existing egg allergy, presenting to the adult clinic for the first time, should be assessed for the likely resolution of egg allergy.

Other egg-related conditions

Egg allergy and asthma

  • Children with egg allergy are at increased risk of other allergic diseases, especially asthma. A careful history should, therefore, be taken to enquire about respiratory symptoms
  • The presence of asthma may increase the potential severity of accidental egg reactions and excellent asthma control should be a priority.

Egg allergy as a risk factor for peanut allergy

  • Infants with egg allergy are at risk of developing peanut allergy. The introduction of regular high-dose peanut into the diet of egg-allergic children under 11 months of age reduces the incidence of peanut allergy at 5 years of age
  • Introduction of peanut in children with egg allergy is discussed in the British Society for Allergy and Clinical Immunology early weaning guidance
  • Infants undergoing SPT or measurement of specific IgE to egg proteins should also be tested for peanut sensitisation, and peanut-containing food introduced alongside other solid foods from around 6 months of age.

Egg allergy and eosinophilic oesophagitis

  • Children and adults with eosinophilic oesophagitis (EoE) respond to elimination of common food allergens, including egg
  • Egg avoidance is usually included as part of an empiric four- or six-food elimination diet
  • Egg SPT is a poor predictor of egg as a trigger for EoE
  • EoE has been reported as a complication of egg immunotherapy. This is usually reversible after early diagnosis and stopping the immunotherapy product.

Use of propofol in egg-allergic patients

  • A commonly-used formulation of propofol contains egg lecithin, derived from egg yolk
  • Propofol administration is safe in adult patients with egg allergy, or who are sensitised to egg. Propofol is safe to use in children with egg allergy.

For recommendations on food protein-induced enterocolitis syndrome to egg, refer to the full guideline.

For recommendations on other egg-related conditions, view the online summary at guidelines.co.uk/456415.article

Immunisation of egg-allergic children and adults

  • Most adults and children with egg allergy can be safely immunised in primary care. The exceptions that require referral for specialist supervision are those who require:
    1. flu vaccine in patients who have experienced life-threatening anaphylaxis to egg (requiring admission to intensive care)
    2. yellow fever vaccine for travel.

Flu vaccine

  • Most flu vaccines are derived from the extra-embryonic fluid of chicken embryos inoculated with specific types of influenza virus
  • The vaccines contain measurable quantities of ovalbumin (egg-white protein), which vary between batches and manufacturers
  • As vaccine manufacture has improved, reports of egg-related allergic reactions to flu vaccines are now largely historical
  • Most current flu vaccines contain very low amounts of ovalbumin (less than 0.12 mcg/ml or 0.06 mcg in a 0.5 ml dose) and can be administered safely in primary care by the intramuscular route, even in those with a previous history of anaphylaxis to egg
  • Egg ovalbumin content of current flu vaccine can be found in the summary of product characteristics (SPC) for the vaccine, or from the May issue of the current year of vaccine preceding the immunisation season. The ovalbumin content of flu vaccines for the forthcoming flu season is published annually by Public Health England
  • The intranasal live attenuated influenza vaccine (LAIV) is also grown in hen’s egg, and therefore, contains egg protein. It is safe to administer in children with egg allergy
  • The ovalbumin content of LAIV is very low (less than 0.12 mcg/ml). It is safe to use and is recommended to be given to children with egg allergy in any setting, including primary care and schools
  • There are no safety data on children who have experienced anaphylaxis to egg requiring intensive care admission, and therefore, these children should be referred to a specialist for supervised immunisation or, where available, consider an egg-free flu vaccine in primary care for children over 9 years of age.

Yellow fever vaccine

  • The yellow fever vaccine (YFV) is a live vaccine cultured in hen’s eggs and contains residual egg proteins
  • Immunisation is relatively contraindicated in egg allergy as most allergic reactions to the vaccine are thought to be related to egg allergy, although other allergens such as gelatine are theoretically possible
  • The potential fatal sequelae from yellow fever means that vaccination should at least be considered
  • Adults and children with egg allergy who require YFV should be assessed in a specialist allergy centre, ideally at least 2 months prior to travel.

Mumps, measles, and rubella vaccine

  • All children with egg allergy should receive their normal childhood immunisations, including the measles, mumps, and rubella, as a routine procedure in primary care.

Rabies vaccine

  • There are two vaccines available: a human diploid cell vaccine that does not contain egg, and purified chick embryo cell (PCEC) vaccine that contains traces of egg protein, including ovalbumin
  • There have been reports of allergic reaction and anaphylaxis to PCEC, some of which may have been related to egg allergy
  • PCEC (Rabipur, GlaxoSmithKline) is relatively contraindicated in individuals with a history of previous egg anaphylaxis. The contraindication is relative, as rabies is almost universally fatal and immunisation for post-exposure prophylaxis outweighs the risk of allergic reaction to the vaccine (Chapter 27, Green Book 2019)
  • Human rabies immunoglobulin, a passive immunisation used for treatment, does not contain egg protein.

Psychological and social implications of egg allergy

  • Any food allergy may adversely affect quality of life, resulting in anxiety and depression. Psychological help and intervention is effective in addressing anxiety and phobias, and promoting adaptive coping strategies. This can be accessed via paediatric psychology services or Child and Adolescent Mental Health Services for children, and Improving Access to Psychological Therapies for adults. Patients with mild-to-moderate egg allergy do not usually require additional psychological support.

For recommendations on the psychological and social impact of egg allergy, view the online summary at guidelines.co.uk/456415.article

 

For recommendations on the management of egg allergy in nurseries and schools and the introduction of egg into the diet of infants from atopic families, refer to the full guideline.

Full guideline:

British Society for Allergy and Clinical Immunology. BSACI 2021 guideline for the management of egg allergy. BSACI, 2021. Available at: onlinelibrary.wiley.com/doi/10.1111/cea.14009.

Published date: 29 September 2021.

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