Predictors of Persistent Peanut Allergy at Age 5 Years

Introduction:

Food allergy has reached epidemic levels in Canada and peanut allergy is the most prevalent and one of the more persistent food allergies among Canadian children and adults. Avoidance or later introduction of peanut has been proposed as a possible cause of the increased rates of peanut sensitization and allergy. Although delaying the introduction of peanut into children's diets is no longer recommended, many parents continue to worry about introducing peanut and some will not introduce peanut into their child's diet without a negative skin prick test to peanut. However, some children who have never had a reaction to peanut can eat and tolerate peanut despite being sensitized (having a positive skin prick test) to peanut.

The purpose of this study is to determine if avoidance of peanut by children with positive skin prick testing to peanut in the first 5 years of life increases the likelihood of developing a persistent peanut allergy by age 5 years. To answer this question, the investigators need to determine which children with positive skin prick testing to peanut have reactions after eating peanut (allergic to peanut) and which are able to tolerate eating peanut (not allergic).

Specific Objectives:

1. To conduct double-blind placebo-controlled peanut challenges among 5-year-old children who are sensitized to and avoiding peanut, to determine if they are allergic to peanut (and need to continue avoiding peanut) or clinically tolerant to peanut (and may continue to eat peanut after passing the challenge)
2. To determine the relative risk of developing peanut allergy among peanut-sensitized children who have been eating versus avoiding peanut.

Challenge Procedure:

Double-blind placebo-controlled food challenges are the gold standard clinical practice for diagnosis of food allergies, and involve the child undergoing separate challenges to the food and to a placebo so that the child, parents, and physicians and nurses administering the challenge are masked regarding which challenge is to the food and which is to the placebo. All children will undergo challenges to both peanut and placebo, in a randomized order. These challenges will not change a child's ability to tolerate peanut, but will determine if children who are avoiding peanut are allergic to peanut (and need to continue avoiding peanut) or clinically tolerant to peanut (and may continue to eat peanut after passing the challenge).

The challenges will be conducted in clinical units set up for food challenges, by a research nurse and a pediatric allergist with expertise and experience in managing food allergies and oral food challenges. Each child will undergo a challenge to peanut on one day and a challenge to placebo on another day. The peanut will be concealed in a vehicle, such as a shake or smoothie. One of the challenges will contain peanut and the concealing vehicle and the other challenge will contain only the vehicle. The challenge foods will be prepared by a team member who is not otherwise involved in the challenges. A study worker not involved in the challenges will also be in charge of randomizing the two challenges to peanut or placebo and of decoding the challenge food identity after both challenges are completed. The children, their families, the research nurse and the pediatric allergist will not know whether the challenge food contains the peanut or the placebo until both challenges have been completed. This procedure helps to distinguish symptoms that occur due to anxiety (equally likely to occur in both the peanut and placebo challenges) and those that are a reaction to peanut (occur only during the peanut challenge).

Children who do not develop any symptoms of anaphylaxis (e.g. hives, swelling, trouble breathing, vomiting, abdominal pain or changes in their level of consciousness) during the challenge or the 2-hour observation period after the challenge will have passed the challenge and will be considered clinically tolerant; they will be encouraged to continue eating peanut at home at least once per week. Children who develop any of these symptoms during the challenge containing peanut will be considered allergic, especially if symptoms did not occur during the challenge containing only the vehicle.