As little as 1/1000th of a peanut can trigger life-threatening anaphylaxis.

In a study published in the November issue of the Journal of Allergy and Clinical Immunology, the Hopkins team recommends that children who outgrow peanut allergy eat concentrated forms of peanut products, such as peanut butter, shelled peanuts or peanut candy, at least once a month in order to maintain tolerance.

"The exact mechanism by which peanut allergy may recur is not known, but we know that the children in our study who ate concentrated forms of peanut frequently had a considerably lower chance of having a recurrence of their allergy," says Robert Wood, M.D., the study's senior author and a pediatric allergist at the Johns Hopkins Children's Center.

Precautions Recommended

According to Wood, an estimated 20 percent of children stop having allergic reactions to peanuts as they grow older. Few studies have been able to clearly assess the rate of recurrence because many such children, understandably, tend to avoid eating peanuts.

"It is common because of an ongoing dislike of peanut or an ongoing fear of a reaction," Wood adds. "That is reasonable because there is a risk of recurrence and reactions could be worse."

As a result, Wood says he and his team continue to recommend that children who eat peanuts infrequently or in limited amounts carry epinephrine injections at all times, and that they continue with annual blood tests to monitor allergy antibodies and assess the risk of recurrence.

Wood also recommends that those children who do eat concentrated peanut products frequently carry epinephrine injections for at least one year after passing an oral food challenge, a highly accurate allergy test in which the child eats small amounts of the suspected allergen in a clinical setting and is watched carefully for symptoms.

Goal: Who's at Risk?

In the study, Wood and colleagues at Arkansas Children's Hospital evaluated 68 children between the ages of 5 and 21 who outgrew a peanut allergy. Each family completed a questionnaire to establish a detailed history of the child's peanut consumption since passing an oral peanut challenge. Twenty-one children also underwent a double-blind, placebo-controlled oral peanut challenge.

Overall, the researchers found that 34 children who consumed concentrated peanut products frequently, and 13 children who ate peanut products in limited amounts but passed the oral peanut challenge, continued to tolerate peanuts.

Three children - all of whom reported eating peanut products infrequently and in limited amounts - experienced an allergy recurrence, yielding an 8 percent recurrence rate. The status of the remaining 18 children was unclear because they ate peanuts infrequently or in limited amounts and declined to undergo the oral peanut challenge.

Although the findings serve as recommendations for families and clinicians managing a child who has outgrown a peanut allergy, Wood hopes future research will help to better identify patients who are truly at risk for a peanut allergy recurrence. "Then we can recommend that these patients continue to avoid peanut for life rather than risk the chance of having a serious allergic reaction in the future when their allergy may recur," he says.

Food Avoidance May Be Unnecessary

In an accompanying study, also in the November issue of the Journal of Allergy and Clinical Immunology, Wood and colleagues report that while severe allergic reactions do occasionally occur with all foods tested during an oral food challenge, these reactions can be reversed with prompt treatment of routine medications, such as short-acting antihistamines.

Therefore, researchers say the risk of a reaction is warranted as long as the challenge is performed under the supervision of an experienced clinician. They also report that no foods were more or less likely than others to cause a severe reaction; for example, severe reactions to eggs were just as common as they were to peanuts.

Without a definitive diagnosis from a food challenge, children may unnecessarily avoid foods like milk, eggs, and peanuts which have significant nutritional benefits. Wood says the second study's findings provide reassurance that food challenges can be safely performed and "we hope this information helps families make a more informed decision about whether or not their child should undergo a challenge," he says.

Peanut Allergies on the Rise

Experts say peanut allergies, which affect approximately 1 to 2 percent of young children and 1.5 million Americans overall, are on the rise. The allergy can be triggered by as little as 1/1000th of a peanut and is the leading cause of anaphylaxis, the life-threatening allergic reaction that constricts airways in the lungs, severely lowers blood pressure, and causes swelling of the tongue or throat, and sometimes leads to death.

Co-authors of the study were David Fleischer and Mary Kay Conover-Walker of the Johns Hopkins Children's Center Division of Immunology and Allergy; and Lynn Christie and A. Wesley Burks of Arkansas Children's Hospital.