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Food allergy

Dr Rajesh Varma

CKS Food Allergy

Patient information website Allergy UK

Definition

Food allergy IgE-mediated
IgE-mediated food allergy follows exposure and sensitization to trigger food allergen(s).
Exposure is usually by ingestion and more rarely by inhalation or skin contact.
It produces immediate and consistently reproducible symptoms which affect skin, gastrointestinal tract, respiratory, cardiovascular, and neurological systems.

Oral allergy syndrome (or pollen-food syndrome)
Localized food allergy which may occur due to cross-reactivity between aeroallergens, such as birch pollen, and fresh vegetables, fruits, and nuts.
As a result, pollen-sensitized people mount an IgE response to epitopes present in fruit and vegetables on oral contact.

Mixed IgE and non-IgE-mediated food allergy
Examples include cows' milk protein allergy, eosinophilic oesophagitis, or eosinophilic gastroenteritis

Food sensitization
The production of serum-specific IgE to food allergens, without the clinical symptoms of an allergic reaction on food exposure

Food allergy Non-IgE-mediated
Cell-mediated mechanisms, such as food protein-induced enterocolitis syndrome which tend to occur in young children, and presents with gastrointestinal symptoms such as vomiting with or without diarrhoea, abdominal cramps, colic, and possible faltering growth.

Food intolerances (non-immune)
Non-immune adverse reactions to foods and/or food additives which are distinct from food allergy.
They often present non-specifically with gastrointestinal symptoms, headache, fatigue, and musculoskeletal symptoms.
Typically, there is a delay in symptom onset and a prolonged symptomatic phase.
They may overlap with symptoms of other conditions such as irritable bowel syndrome or fibromyalgia.

The exact cause is unknown, but they may be due to:

  • enzyme deficiencies: lactase deficiency (causing diarrhoea, abdominal pain, and increased flatus after ingestion of dairy products)

  • pharmacological causes (such as caffeine or tyramine in cheeses)

  • no clear mechanism (including reactions to food additive flavours and preservatives, such as glutamates and sulphites).

Allergens

Other common cross-reactions include:

  1. Between peanuts, tree nuts, and sesame.

  2. Latex-fruit syndrome: 30–50% of people with known latex allergy are allergic to banana, kiwi, avocado, tomato, potato, and chestnut owing to latex allergens cross-reacting with plant-derived food allergens.

  3. Oral allergy syndrome include cross-reactivity between:

    Birch pollen with apple, pear, peach, plum, cherry, apricot, carrot, celery, parsley, almond, and hazelnut.

    Timothy grass (a common agricultural grass) with Swiss chard and orange.

  • Cows' milk

  • Eggs

  • Peanuts and other  legumes such as soybean, pea, and chickpea

  • Tree nuts (such as walnut, almond, hazelnut, pecan, cashew, pistachio, and Brazil nuts) 

  • Shellfish (such as shrimp, crab, and lobster) 

  • Fish

  • Wheat

  • Celery, mustard, sesame, lupine, and molluscan shellfish — in Europe

Risk factors

  • Pre-existing food allergy

  • Atopic eczema:  early-onset atopic eczema is associated with the development of egg, milk, and peanut allergy

  • Family history of food allergy and/or atopy

Complications

  1. Severe and life-threatening reactions (including anaphylaxis)
    Allergy to peanuts, tree nuts, fish, and shellfish are associated with a higher risk of anaphylaxis.

  2. Stress and anxiety

  3. Restricted diet and malnutrition
    The risk of inadequate nutritional intake and faltering growth in children, if food allergens that contribute essential nutrients are eliminated.

Prognosis

  1. Most children outgrow their food allergy by adulthood, particularly egg and wheat allergy

  2. Certain food allergies are most likely to persist, such as peanuts, tree nuts, fish, and shellfish

  3. Factors which may increase the likelihood of severe food allergy and/or anaphylaxis include:

  • Atopy (asthma, atopic eczema, allergic rhinitis)

  • A history of previous systemic allergic reaction

  • Allergy to the food classes of peanut, tree nut, fish, or shellfish.

Diagnosis of IgE-mediated food allergy

Rapid onset (seconds/minutes to 1–2 hours) classical symptoms after ingestion of a specific trigger food, and typically resolve before 12 hours:

Systemic (which suggests life-threatening anaphylaxis)
Respiratory distress, severe wheezing, hypotension, tachycardia or bradycardia, drowsiness, confusion, collapse and loss of consciousness.

Skin
Urticaria, angio-oedema (most commonly of the lips, face, and around the eyes), erythema, generalized itching, and flushing.

Respiratory
Persistent cough, hoarseness, wheeze, breathlessness, stridor; nasal discharge, congestion, itching, and sneezing.

Gastrointestinal
Nausea, vomiting, diarrhoea, and abdominal pain.

Oral allergy syndrome (pollen-food syndrome)
Typically mild, transient localized urticaria and associated tingling, itching, and swelling of the lips, tongue, and throat, often with co-morbid allergic rhinitis symptoms, after ingestion of fresh fruit or vegetables. Symptoms tend to be worse when the pollen count is high.

Note: be aware that a diagnosis of primary nut allergy and oral allergy syndrome may co-exist.

Latex-fruit syndrome
People with known latex allergy may present with a variety of symptoms including urticaria, angio-oedema, oral symptoms, or anaphylaxis following ingestion of certain fruits and nuts.

Consider a diagnosis of food allergy in people who have unexplained persistent symptoms of:

  • Atopic eczema

  • Faltering growth

Differential diagnosis

  1. Post-viral acute spontaneous urticaria and angio-oedema

  2. Carcinoid syndrome — may present with watery diarrhoea and upper body flushing; symptoms may be provoked by eating or alcohol ingestion.

  3. Food intolerance

  4. Irritable bowel syndrome

  5. Food poisoning and toxic reactions — including scombroid poisoning, which may present with paraesthesia, burning sensations, headaches, and itch after spoilt food ingestion.

    Scombroid poisoning is due to bacterial production of excess amines, particularly histamine, on food.
    Most cases derive from tuna, mackerel, herring, marlin, anchovy, or mahi-mahi fish.

  6. Food refusal or aversion

Assessment of suspected IgE-mediated food allergy

  1. Asking about causal foods, symptoms, timing in relation to the suspected allergen exposure

  2. Any co-morbid atopic conditions  [asthma, atopic eczema, and/or allergic rhinitis]

  3. Any symptom response to dietary restrictions or food reintroduction.

  4. Examining for nutritional status (failure to thrive); weight, length/height, and calculation of body mass index (BMI)

  5. Allergy Testing
    Skin prick testing and/or serum-specific IgE.
    [Skin prick test sensitization may be suppressed by recent antihistamine, beta-blocker, tricyclic antidepressant (TCA), and topical corticosteroid use]
    Some people have positive test results but do not develop symptoms of clinical allergy (food sensitization only and a false positive result).
    Allergy testing may also be used to assess whether tolerance has developed.
    If the results of allergy testing do not correspond with the clinical history, an oral food challenge may be needed to confirm the diagnosis.

Management

Arrange immediate ambulance transfer to Accident and Emergency if there are systemic symptoms or suspected anaphylaxis with or without angio-oedema

Referral to a dietitian

  1. If there are nutritional concerns

  2. Food allergen avoidance or reintroduction advice is needed: tolerance develops in steps, with cooked forms (e.g. cake for egg allergy) tolerated before raw equivalents (e.g. scrambled egg).

  3. Person is already on a restricted diet

Referral to an allergy specialist

  1. The person is at increased risk of anaphylaxis, such as history of
    systemic symptoms or severe reaction
    food allergy and co-morbid atopy (asthma, atopic eczema, rhinitis)

  2. Allergy testing and interpretation is needed
    Skin prick testing and/or serum-specific IgE.

  3. Diagnosis is uncertain

General Measures following referral advice

  1. Providing an individualized written allergy management plan.

  2. Advising on prompt recognition and management of acute symptoms following accidental or new exposures

    immediate use of oral antihistamines for non-severe symptoms

    immediate use of adrenaline auto-injector therapy for suspected anaphylaxis

  3. Providing advice and education on food allergen avoidanceincluding foods that may be cross-reactive and which foods are suitable alternatives.

  4. Advice on interpreting food labels

  5. Advice about allergen avoidance during travel, including air travel and travelling abroad.

  6. Advise food allergy may impact on vaccinations (particularly egg allergy).

  7. Annual review

  8. Oral allergy syndrome.
    Recommend referral to an allergy specialist.

    Patients need adrenaline auto-injector while they await specialist confirmation (important to distinguish oral only reaction from a more severe systemic allergic reaction with urticaria, erythema, pruritis, gastroenterological and respiratory symptoms or even anaphylaxis)

    May need both skin prick testing and specific IgE blood tests to identify problem pollens.