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What to tell parents about peanut allergy

Allergies are becoming increasingly common, and parents may fall prey to unproven fringe therapies. Professor Gideon Lack gives an evidence-based guide to diagnosis and treatmen

Allergies are becoming increasingly common, and parents may fall prey to unproven fringe therapies. Professor Gideon Lack gives an evidence-based guide to diagnosis and treatmen

The prevalence of peanut allergy has unequivocally increased over the last two decades in developed countries. This may relate to the avoidance or introduction of peanuts into the diet of young children, or it may be related to generic factors associated with the overall rise in allergic disorders.

Almost one child in 50 is affected by nut allergy (either peanut or tree nut). Nuts remain the most common cause of fatal and near-fatal food-induced allergic reactions. The fear of accidental nut exposure and the inability to predict the severity of future reactions make a significant impact on the quality of life of both sufferers and their families.

After milk and egg, peanut is the most common cause of childhood food allergy in the UK and US. Around one child in 70 suffers from peanut allergy and the prevalence seems to be rising. Peanuts are biologically legumes (pulses) rather than tree nuts (cashews, almonds, walnuts etc) but they are often considered nuts.

Nut-induced allergic reactions generally occur with first known exposure, which implies that ingestion may not always be the route of sensitisation.

Food-induced allergic reactions usually occur soon after the food is eaten – usually within minutes and rarely take longer than one hour. Reactions are the result of the body releasing chemical mediators such as histamine. These substances cause hives, hypotension and asthma.

By far the most common type of reaction involves angiodema and urticaria. The child's behaviour may also acutely change – they may become clingy and scared, and often this is the first sign of an allergic reaction. Abdominal pain may also be present. More severe reactions (anaphylaxis) may involve the airways (wheezing or wheezy cough, throat swelling and difficulty in breathing) and cardiovascular system (hypotension).

Peanut allergy most commonly presents during early childhood. The first allergic reaction usually occurs the first time that peanut is eaten. Children most at risk of developing peanut allergy are those from an allergic family, who suffer from eczema or egg allergy.

At-risk infants include those born to allergic parents and those who develop early onset eczema and/or egg allergy.

Tests

Allergy tests predict for the likelihood of future reactions, but are not reliable predictors of severity. The diagnosis of nut allergy requires a combination of the medical history, allergy tests and, occasionally, oral food challenges.

There are two scientifically valid allergy tests– skin-prick and specific IgE blood tests.

Skin-prick tests

These are the most common test done in an allergy clinic. They help determine whether a child is at risk of an immediate-type allergy to the substance being tested by examining the reaction to allergen extract on the skin.

Specific IgE blood tests

Blood can be drawn for the measurement of the allergy antibodies (immunoglobulin E). This may be performed in addition to the skin tests or if skin tests cannot be performed, for example, if antihistamines have been taken in the days before the skin test, or if they have extensive eczema that prohibits skin testing.

Supervised incremental oral food challenge tests

These may be conducted where the combination of clinical history and allergy testing is unable to provide a certain diagnosis of nut allergy.

Children do not usually grow out of peanut and tree nut allergy, unlike milk and egg allergies. Nut allergies may also co- or cross-react with other allergies: children with peanut allergy, for example, are seldom allergic to only one food with the association between peanut allergy and tree nut allergies and/or sesame seed allergy being particularly strong (60% and 25%, respectively).

Warning labels

Avoiding peanuts can be difficult and expert advice should be obtained from a specialist dietician, who will assist with interpreting food labels as peanuts may appear as ‘groundnut' or ‘arachis'. Nuts may also be present in unexpected products such as massage oils or as vehicles for medicine. Arachis and peanut oils are best avoided by peanut allergic individuals.

Children who are allergic to a nut are usually advised to avoid the whole family of nuts because of the risk of cross-reactivity and cross-contamination. This decision can be reviewed when children are older and sequential allergy tests have been done.

Parents may ask about warning labels on food that says ‘produced in a factory where nuts may have been used'. These foods should be avoided.

Emergency management

Children with nut allergies require a personalised emergency management plan. This should be issued to both parents and the school or nursery. The plan should be easily accessible and should accompany the emergency medications. It will outline in a step-wise fashion exactly what should be done in case of an allergic reaction.

In the majority of instances this will simply involve giving an antihistamine. The antihistamines are all of similar efficacy but chlorphenamine has a long track record in the UK, is ubiquitous, licensed for children and cheap; so it is widely used.

For moderate-severe allergic reactions, an adrenaline autoinjector must be administered in the muscle on the outer aspect of the child's thigh.

All nut-allergic children require an adrenaline autoinjector. The European Academy of Allergology and Clinical Immunology recently recommended that all children with a food allergy and co-existent asthma should be issued with self-injectible adrenaline. A history of only a mild peanut or tree nut allergy is a relative indication for an adrenaline autoinjector.

Other therapies

There are many dubious types of diagnosis and treatment that GPs can help parents avoid. As detailed above, there are only two validated allergy tests; the skin-prick test and specific-IgE blood tests. No other allergy tests should be performed and if patients have undergone such testing, results must be disregarded as they may lead to unnecessary dietary avoidance and may even prove dangerous if the correct allergens are not identified.

Future therapies

There are exciting therapeutic prospects for the treatment of peanut allergy including anti-IgE therapy, desensitisation and vaccination. All these strategies are currently undergoing trials. However, at present, the only broadly available strategy for the prevention of peanut-induced allergic reactions remains strict avoidance.

Resources for parents

The UK Anaphylaxis Campaign (www.anaphylaxis.org.uk) can put parents in touch with other children and families who suffer from allergies. An identification bracelet from Medic Alert (www.medicalert.org.uk) may also be useful. Other helpful sources of information are Allergy UK (www.allergyuk.org), Alert4Allergy (www.alert4allergy.org/) and the National Eczema Society (www.eczema.org).

LEAP study

The LEAP (Learning Early about Peanut Allergy) study is an interventional research study of the best dietary strategy to prevent peanut allergy. It is based at the Evelina Children's Hospital, part of Guy's & St Thomas' NHS Foundation Trust in London.

The study is currently recruiting infants (under 11 months) from across the UK who are at increased risk of developing peanut allergy – those with eczema and/or egg allergy. Half of the participants are randomly assigned to receive age-appropriate peanut-containing foods while the other half are advised to avoid peanut.

Participants are closely monitored by a team of doctors, nurses and dieticians to ensure both nutritional and immunological safety. They also receive allergy testing, dietary counselling, and physical examinations and are asked to provide occasional blood samples that are used to examine differences in immune system development in each of the study groups.

When participants reach the age of five, an assessment of the relative rates of peanut allergy will be made. It is hoped that the findings will influence public health policy on the primary prevention of peanut and other food allergies.

For further information and details of how to refer patients to the LEAP study, interested GPs should contact Professor Gideon Lack, 020 7188 9784.

Email – info@leapstudy.co.uk

Website – www.leapstudy.co.uk

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