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Childhood nut, food and vaccine allergies

Consultant immunologist Dr Andrew Clark outlines the latest on childhood nut, food, milk and vaccine allergies as well as upcoming causes of allergy in children.

Consultant immunologist Dr Andrew Clark outlines the latest on childhood nut, food, milk and vaccine allergies as well as upcoming causes of allergy in children.

Peanut allergy

The prevalence of peanut allergy has risen over the past decade and it now affects 1.5% of five-year-olds. The most frequent age at presentation is six to 24 months, usually after the first apparent exposure, but it can occur for the first time in older children.

Urticaria around the mouth is common in peanut allergy with lip swelling and angioedema of the eyes. Generalised urticaria also occurs, and in a third of cases there is airways narrowing, usually mild wheeze or laryngeal oedema.

Severe reactions occur in about 10% of cases and are usually manifest by severe wheeze and dyspnoea. In the presence of a typical clinical history the diagnosis can be confirmed by a positive skin or serum IgE test.

The cornerstone of good management of peanut allergy is good allergen avoidance advice, which should concentrate on how to check food labelling and situations when accidents are most likely to occur, usually when the child is out of parents' direct supervision, for example birthday parties for toddlers, or eating out for teenagers.

Although it seems straightforward to advise a family to avoid nuts, there are caveats. Food warnings, for example, may be in small print, hidden under a flap or give the allergen an alternate name (for example, arachis for peanut).

Labels such as ‘may contain traces of nuts' are often misinterpreted as meaning that there is only a minor risk and it is safe to eat the food, especially if it had previously been tolerated. But the amount of potential contamination is not limited to traces and such products have even been found to contain whole nuts, so we advise nut allergy sufferers to avoid foods labelled as such, especially chocolates, cakes and biscuits.

Most supermarkets can supply lists of nut-free foods on request and the anaphylaxis campaign provides essential updates on food warnings.

We advise children with peanut and/or nut allergy to avoid all nut types to reduce the risk of developing further allergies.

Avoidance information should be disseminated to the entire family and nursery staff, school catering staff, and teachers.

Up to 20% of young children with mild peanut allergy may grow out of it, but it is not known if peanut allergy will recur in these children.

Tree nut allergy

Tree nut allergy is also increasing in prevalence, especially among children with peanut allergy. Allergy to brazil nut accounts for 16% of reactions to peanut or nuts followed by almond, hazelnut, cashew and walnut.

The clinical features of these allergies are different from those of peanut. First, they occur mostly in older children or adults, although they can occur in infants. Second, brazil and walnut in particular seem to provoke predominately upper airways symptoms of pharyngeal and/or laryngeal oedema and therefore a greater proportion of reactions are severe. Tree nut allergy also seems to be more persistent than peanut allergy and resolution is rare.

Egg allergy

Egg allergy begins in infancy and again is almost always accompanied by urticaria, although wheeze and breathlessness can occur uncommonly. The natural history is quite different from that of nut allergy as about 50% will begin to grow out of egg allergy by two years of age and 80% by five years.

Egg allergens are heat labile, and well-cooked egg is less allergenic than lightly cooked or raw egg. For those with a history of mild allergic reactions to egg and no asthma, from the age of three, egg can be reintroduced at home in a series of step-wise increases.

Initially children may tolerate well-cooked egg, such as in sponge cake, and some months later lightly cooked egg – a hard-boiled egg for instance – and finally a soft-boiled egg.

The pace of reintroduction should be guided by the history of previous reactions, but a six-monthly interval usually works well. Any reactions are usually minor and the previously tolerated form of egg should be continued for a further six months.

Exceptions occur:

• where there has been a history of airways narrowing during a reaction

• where there has only ever been trace exposure such as skin contact, and therefore sensitivity is unknown

• where there is asthma, in which case specialist referral is warranted.

MMR vaccination

All children with egg allergy should receive MMR vaccination, even if the allergy to egg is severe. Current guidelines recommend that children with a history of current asthma, or those with airways narrowing during egg reactions, should be vaccinated in hospital. All other children can be safely immunised in primary care, where facilities for treatment of anaphylaxis should be available. Influenza vaccination is contraindicated in children with egg allergy.

Milk allergy

A proportion of children with eczema have hypersensitivity to cow's milk protein. This may be associated with immediate-type

IgE-mediated response (for example, facial angioedema) or delayed-type hypersensitivity (for example worsening of eczema and/or gastro-oesophageal reflux).

Allergy tests for IgE to cow's milk protein will only highlight those with immediate-type responses. The only practical way to demonstrate delayed-type allergy to cow's milk protein is to perform a complete dairy exclusion diet for three months, followed by milk challenges on at least two occasions.

During dairy avoidance a highly hydrolysed or elemental formula is recommended for boys aged less than six months old. Allergy to soya is common in infants who are allergic to cow's milk protein and goat's milk should not be used as there is a risk of further sensitisation, allergy and anaemia. For children who have been weaned, dairy products such as cheese and yoghurts should also be avoided.

From age two to three, cow's milk formula could be reintroduced in mild cases as milk intolerance usually resolves.

Up-and-coming food allergens

Allergies to sesame seed and kiwi fruit are seen more commonly now, reflecting increased exposure to these foods. Both can provoke severe allergic reactions and warrant prompt avoidance advice and supply of emergency medication.

The prevalence of allergy to several types of tree nut appears to be increasing, for example cashew, pistachio and pecan. Pine nuts can also rarely cause IgE-mediated reactions. Coconut allergy is rare and we do not advise peanut or tree nut allergic patients to avoid this food, except in foods where contamination with nuts is possible.

Dr Andrew Clark is consultant immunologist at Addenbrooke's Hospital in Cambridge

This article is an extract from Practical Paediatric Problems in Primary Care, published by Oxford University Press, edited by Mr Michael Bannon and Professor Yvonne Carter ISBN 978-0-19-852922

Peanut allergy

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