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Controlling and treating childhood food allergies

ow big is the problem?

Prevalence of all common allergic diseases in the developed world is high and rising. Food allergy is no exception, having risen five-fold between 1982 and 1995. The prevalence of allergy to peanuts in childhood has trebled over the past decade (now affecting 1.5 per cent of children). Up to 33 per cent of the population believe they have intolerance to a particular food. Food allergy in this article refers to immediate-type hypersensitivity reactions and is present in 3-4 per cent of the population. Cows' milk, egg and nuts (peanut and tree nuts) account for the majority of food-induced allergic reactions.

Most allergic reactions to foods are mild and involve only cutaneous features but the severity of reactions varies greatly between individuals, as does the severity of subsequent reactions in the same individual. Some patients may go on to have life-threatening reactions.

Looked at another way, food allergy is the commonest cause of childhood anaphylaxis in the UK (41 per cent of cases) and accounts for 16 per cent of cases at all ages. Peanuts and nuts cause the vast majority of fatal and near-fatal allergic reactions to foods (94 per cent).

What are the typical features?

There is almost always a personal (96 per cent) and/or family history of allergy (most commonly eczema, asthma, allergic rhinitis or another food allergy). A history of prior ingestion is not essential to make the diagnosis as up to 80 per cent of peanut-allergic individuals react to peanut on their first known ingestion, suggesting prior occult sensitisation.

A majority of patients' worst-ever reactions to foods are mild and involve only cutaneous (erythema, urticaria and/or angioedema) or gastrointestinal (such as vomiting) features. However, some reactions involve airway narrowing (wheeze or laryngeal oedema) and occasionally severe dyspnoea (12 per cent of nut-induced reactions). Hypotension, an early feature of severe reactions to parenterally administered allergens (such as intravenous drugs), is unusual in food allergy and tends to occur secondary to hypoxia.

Another characteristic of food reactions is rapidity of clinical symptom onset (within 30 minutes for food allergens).

A majority (80 per cent) of children with egg and milk allergy stop reacting to these foods by five years of age. The exception is children who suffer severe reactions, who can continue into adulthood. Peanut and nut allergy is more resistant and only 20 per cent of children with mild peanut allergy have a chance of growing out of it.

Diagnostic tests

The gold standard for diagnosing food allergy is the double-blind placebo-controlled food challenge: this is used mostly as a research tool. Diagnosis can be made by demonstrating a history of a typical acute hypersensitivity reaction (onset of angioedema, urticaria, and erythema within minutes of ingestion) together with evidence of specific IgE to the relevant antigen (known as 'sensitisation').

It must be remembered that twice as many patients are sensitised as those who actually have clinical allergy. In genuine food allergy the allergen responsible is usually clear from the history. There is no place for sending off a battery of random specific IgE tests, without a clear history of a reaction to a particular allergen, hoping for a 'hit', as this is likely to result in a false positive.

Skin-prick tests performed by an experienced operator (such as an allergy clinic) offer the best method for detecting sensitisation. They are more discriminatory than CAP-RAST tests, with fewer false negative. Other proprietary 'tests' such as the 'VEGA' have no place in diagnosis.

Management challenges

There are several problems in the management of food allergy. There is a wide age range and spectrum of severity and little way of predicting who is at risk of future severe reactions.

Patients with food allergy of all severities are often prescribed Epipen (adrenaline autoinjector) with little thought given to training or advice on allergen avoidance.

Epipen alone is not enough and more emphasis should be placed on good avoidance advice: 75 per cent of nut-allergic children in the UK, without specialist advice, have a further reaction within five years.

Reactions may become more severe over time yet two-thirds of children with a history of anaphylaxis do not have emergency medication, an emergency treatment plan or a teacher on site trained to administer adrenaline.

Only a third of parents whose children are prescribed adrenaline can correctly demonstrate Epipen use. Rapidity of onset and potential severity of reactions means food-allergic patients should have appropriate self-medication available and be trained in its administration.

Management plans

We developed a comprehensive management plan for patients with food allergy and assessed its efficacy in 567 nut-allergic adults and children over a median of two years. The severity of each patient's worst-ever reaction was graded and appropriate medication for self-administration was prescribed (oral antihistamine for mild reactions and injectable adrenaline for reactions involving airway narrowing, or if there was a history of asthma). Asthma was considered an additional risk factor because patients who suffer fatal or near-fatal reactions mostly have asthma and it is often poorly controlled.

The management package consisted of written and verbal avoidance advice, an emergency treatment plan including appropriate medication for self-administration and training of patients, parents and schoolteachers. Patients were reviewed annually and patients, carers and teachers were retrained in all aspects of the plan.

Over a median of two years, only 15 per cent had a further reaction and it was of reduced severity, requiring either no treatment or oral antihistamine alone. Intramuscular adrenaline was used in nine reactions with airway narrowing; all patients improved and there were no unwanted effects.

This approach improves the outcome of peanut and nut allergy in children and provides a model of good practice for prevention and treatment of all forms of food allergy in childhood. It is best implemented by an allergy clinic.

Childhood food allergies have increased dramatically,

yet training and advice on allergen avoidance are

thin on the

ground, writes

Dr Andrew Clark

Controlling and treating childhood food allergies

Take-home messages

 · Food allergy in children is a growing problem

 · A third of the population believe they have food intolerance

 · The real prevalence of food allergies in the population is 3-4 per cent

 · Most food allergies are mild

 · 80 per cent grow out of milk and egg allergies by age five

 · Genuine food allergies usually have a clear allergen

 · Epipens may be being inappropriately prescribed

 · Training and advice on allergen avoidance can reduce occurrence and severity of reactions

Key allergenic foods

 · Cow's milk (particularly in infants)  · Eggs

 · Legumes (soya and peanuts)  · Fish and shellfish

 · Fruit and vegetables (usually oral allergies)  · Tree nuts

 · Cereals (particularly with exercise-induced anaphylaxis)

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