Preventing peanut allergy
Peanut allergy is recognised as a public health concern in the uk. The prevalence is 1.5 per cent and is increasing.1 It is the most common cause of fatal and near-fatal food-induced allergic reactions.2 The fear of accidental peanut exposure and the inability to predict the severity of future allergic reactions result in a decreased quality of life for peanut allergic individuals and their families.
Peanut allergy most commonly presents during early childhood. The index allergic reaction usually occurs soon after the first known oral ingestion of peanut. This suggests that peanut sensitisation does not always occur via the oral route. Alternate routes of exposure may include abraded skin or inhalation. Known risk factors for the development of peanut allergy include egg allergy and eczema during infancy.3
Children with peanut allergy are rarely allergic to only one food, with the association between peanut allergy and tree-nut allergies and/or sesame seed allergy being particularly strong (60 per cent and 25 per cent respectively).4
Unlike egg and milk allergy, which are outgrown in 85 per cent of affected children by the age of seven, peanut and tree nut allergy are only outgrown in 25 per cent and 9 per cent of cases respectively.5 Children who outgrow peanut allergy generally do so by the age of five years. Favourable prognostic factors include exclusive peanut allergy, early clinical presentation, low IgE values at the time of presentation and IgE values that rapidly diminish with time. Children who experience only mild allergic reactions (skin symptoms only) and who present during the first 24 months of life may have an increased chance of outgrowing their food allergy. However, peanut allergy may recur. Recurrence is associated with continued avoidance of the allergen.
The only broadly available strategy to prevent peanut-induced allergic reactions is strict avoidance of peanut exposure. Peanut-allergic individuals (and their families) require training in the recognition of allergic symptoms. They also need to be provided with, and trained in the administration of, emergency medications, such as pre-loaded intramuscular adrenaline and antihistamines.
Strategies for the primary prevention of peanut allergy have focussed on the avoidance of peanut consumption during periods of ‘immunological vulnerability', such as during infancy, pregnancy, and while breastfeeding. In the UK, parents of infants identified as at risk of allergy (having a sibling or parent with an atopic disease) are advised that they ‘may wish' their child to avoid peanut exposure for the first three years of life. The recommendations have a high uptake, but despite this the prevalence of peanut allergy has continued to rise in the UK and in other countries with a similar policy.
Clinical observation and cross-sectional prevalence studies suggest that peanut allergy is far less prevalent in countries such as Israel and South Africa, despite children in those countries enjoying early and high-dose peanut protein consumption. It has also been demonstrated recently that delaying exposure to cereal grains until after six months may increase the risk of developing wheat allergy, and that the early consumption of wheat is not a risk factor for the development of wheat allergy or coeliac disease.6 It remains unclear whether children at risk of developing peanut allergy should avoid or eat foods containing peanut.
The Learning Early About Peanut Allergy (LEAP) study aims to determine the best dietary strategy to prevent peanut allergy in children at risk.
The study, based at Evelina Children's Hospital, London, aims to recruit 480 infants (under 11 months of age) from the Greater London area who are at increased risk of developing peanut allergy (such as those with eczema and/or egg allergy). Half the participants are randomly assigned to receive age-appropriate, peanut-containing foods. The other half are advised to avoid peanut. An objective determination of the relative rates of peanut allergy will be made when participants reach the age of five. Laboratory studies run in parallel to gain insight into how early exposure to peanut may lead to a state of tolerance or allergy.
It is hoped that the findings will influence public health policy on the primary prevention of peanut and other food allergies.
For information on the LEAP study, contact 020 7188 9784, firstname.lastname@example.org, or visit www.leapstudy.co.ukAuthor
Dr George du Toit
MBBCh FCP FRCPCH FAAAAI
paediatric allergy consultant, co-investigator of the LEAP study, Evelina Children's Hospital at St Thomas' Hospital, London