Food Allergy: Science and Clinical Practice

Allergy Research Foundation
Report by Cressida Boyd

The prevalence of allergy
Professor Peter Burney of Imperial College, London presented research showing that the prevalence of respiratory allergies and wheeze is increasing. Those born later in the last century have a higher sensitivity – suggesting that there is an inbuilt susceptibility to respiratory disease, rather than the condition having an environmental cause.

The epidemic of sensitisation is real and likely to increase in older age groups. However more recent research suggests that there is less sensitisation present in children born in the last few years.

Child food allergy: How does it start? Why does it stop?
Professor Gideon Lack, paediatric allergist at Evelina Children’s Hospital in London reminded the conference of current governmental advice regarding peanuts: if there is a history of eczema, hay fever, asthma or allergy in either parent’s family, peanuts should be avoided during pregnancy. Once the baby is born, there is further advice to breastfeed exclusively for the first six months.

Development of allergy depends on timing, routes of exposure and immunity. There may be a connection between early weaning and development of allergies, or between avoidance of certain foods and development of allergies.

The early presence of eczema in babies is associated with food allergy. Babies who develop eczema in the first six months have a two-times higher risk of developing food allergy than babies who develop eczema in their second six months. Could this be linked to an increased use of cortico-steroids?

Studies carried out by Dr Lack’s team suggest that whether the mother ate peanuts during pregnancy was far less important than the amount of peanut consumed by the family: the higher the peanut consumption, the higher the chance of a child developing peanut allergy.

Peanuts covered in chocolate were less likely to cause allergic reactions than peanut butter, which is sticky and gets everywhere. Data collected measured levels of peanut particles in the home before and after peanut consumption. Extremely high levels of peanut allergen remained after seven days of repeated scrubbing of taps, tabletops and walls.

Professor Lack is currently running the LEAP study to determine whether the avoidance of peanut in atopic infants or the measured, repeated consumption of peanut-containing foods is more or less likely to lead to peanut allergy. A study of Israeli and British Jewish children suggests that early consumption of peanuts may prevent infant allergy.

A clinician’s perspective
Dr Michael Tettenborn of Frimley Children’s Centre admitted that there remained a great deal about allergy that was not fully understood.

Studies of the most favourable times for weaning are contradictory while the same patient can have a positive skin prick and a negative intra-mucosal test for the same substance because different parts of the immune pathway react to the tests. He strongly advised GPs to act fast and test if there is the slightest suspicion of allergy.

Non-gastrointestinal manifestations of food allergy
Professor Jonathan Hourihane of University Hospital in Cork said that it was rare for someone to suffer from eczema alone. Similarly, food allergy is more than a gastro-intestinal disease: it coexists with other atopic conditions. Sensitisation is common in children with eczema. Different foods have different patterns of reactivity.

Physical manifestations of allergy occur in the skin, airways and elsewhere, but Professor Hourihane has been investigating the equally important social and psychological manifestations of allergy: the sufferer’s quality of life, that of their mother, father and siblings, and the constant fear of death in anaphylactic patients. So far he has found that mothers generally have a lower quality of life than fathers, with higher stress and anxiety levels. Children with allergies have isolation and separation anxiety, and the parents have no conviction that the child will be treated effectively in the event of a reaction.

An allergist’s correct diagnosis can remove some of the anxiety. Professor Hourihane emphasised that food allergics need more attention as treatments develops. He has compiled a validated quality-of-life questionnaire that is available for all GPs and allergists.

Food allergy and anaphylaxis
Dr Pamela Ewan from Addenbrooke’s Hospital, Cambridge described a seven-fold rise in anaphylaxis between 1991–2001. She emphasised the considerable need of allergy care in the primary sector.

Between 2001–2005 there was a 5% increase in GP - reported anaphylaxis as a result of better record-taking and understanding, and increased occurrence. Food is a major cause of anaphylaxis, so diagnosis of food allergy is important.

According to her calculations, 7% of children and 3% of the adult population of Britain have food allergies, and new allergies are appearing to pulses, fruits and vegetables. There are pollen-like allergens in fruits and nuts while different proteins in the same nut can cause different sensitivities and reactions.

Peanut allergy maybe more common but the reaction to the cashew nut allergen is more severe. Skin-prick tests of 1,000 people with nut allergy, only resulted in 46% positive tests, which suggests that skin prick tests may not always be helpful for nut allergy.

Dr Ewan suggests a management plan for every allergy sufferer and their family. She also briefly described her work on an oral administration programme involving about 60 children. One child who was previously anaphylactic to peanuts can now tolerate a little peanut. But she stressed that this method is risky, time-consuming and stressful.

Pollen sensitisation and cross-reactions to foods
Isabel Skypala from the Royal Brompton Hospital in London, continued Dr Ewan’s brief introduction to pollen-like allergens by describing the similar molecular structure of fruit and vegetable allergens, which may lead to cross-reactions – what she calls ‘pollen-food syndrome’, a more accurate description than the more common ‘oral allergy syndrome’. Hayfever sufferers, for example, have begun to report reactions to foods.

However, reactions are not uniform. In Spain people might react to one protein in an apple, and in the Netherlands to a totally different one. However, fresh apples are less allergenic than stored apples. High fresh fruit intake is linked to improved asthma control.

Evidence for delayed food allergy in pollen allergic patients
Dr Beatrice Jahn-Schmid of the Medical University, Vienna described her work investigating, on a molecular level, the pollen-food syndrome that Isabel Skypala is researching.

Advances in the diagnosis
Dr Michael Perkin from St Thomas’s Hospital in London described present procedures, and advances, in the diagnosis of food allergy. He stressed that exclusion diets should not be maintained without good reason as he is seeing an increase in seriously malnourished children.

Currently there is a three-part diagnosis for food allergy:

• History, as related by parent and child, which is usually around 50% accurate

• Allergy testing – only 30–40% of children with food specific IgE are actually allergic

• Food challenge, which is time consuming and risky

None of these, Dr Perkin suggests, are foolproof. There has been a move to minimise food challenge. However, there are weal sizes, produced by skin prick testing, above which all food challenges are positive although there is a wide variation in levels. There needs to be a way of differentiating between sensitisation and allergy to reduce the need for oral challenge. Because specific IgE levels do not indicate type or severity, it is very hard to predict the severity of reactions. Differences in skin-prick test extract (dried egg, raw egg, albumen, yolk, etc) and differences in the populations may distort research results so it is good idea to gather data from one’s own practice.

First published in 2009

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