Today's Kids Slower to Outgrow Milk and Egg Allergies

By Judith Groch, Senior Writer, MedPage Today
Reviewed by Zalman S. Agus, MD; Emeritus Professor
University of Pennsylvania School of Medicine.

BALTIMORE, Dec. 14 -- Children don't always outgrow milk and egg allergies as quickly as predicted by common wisdom and the conditions may persist well into adolescence

So found two retrospective studies, one on milk and the other on egg, with some overlap, reported Johns Hopkins investigators online in the Journal of Allergy and Clinical Immunology.

The prognosis for a child with a milk or egg allergy appears to be worse than it was two decades ago, said Robert A. Wood, M.D., a co-author of both studies, and colleagues.

Rather than outgrowing the allergies by the time they start school, only about 20% to 40% of children do so with milk and about 4% to 26% with egg. Twenty percent of patients with milk allergies and 30% of those with egg allergies don't develop tolerance till age 16, found the researchers.

"We may be dealing with a different kind of disease process than we did 20 years ago," Dr. Wood said. "Why this is happening we just don't know."

Cow's milk allergy, the most common allergy, affects 2% to 3% of infants and young children, and egg allergy, second after milk, affects 1% to 2% of young children, the researchers wrote.

The purpose of both studies, which followed children for more than 13 years, was to define the rate of allergy resolution over time and identify the clinical and laboratory features that may predict the outcome with passing years. In both studies the children came from pediatric allergy clinics.

In the milk study, the investigators collected a clinical history, test results, and final outcomes for 807 children (a 2:1 male:female ratio) with IgE-mediated cow's milk allergy. Data collection began in 1993.

The findings of this study are in marked contrast to an often quoted study that suggested that three-quarters of children with milk allergy outgrew their condition by age three, the researchers said.

In the Hopkins study, only one-fifth of the children outgrew the milk allergy by age four.

Patients were considered tolerant after they passed a challenge or experienced no milk reaction in the previous 12 months and had a cow's milk IgE of <3 kU/L.

When tolerance was defined in this way, resolution rates were 19% by age four, 42% by age eight, 64% by age 12, and 79% by age 16. Although it took time, most, but not all, children did outgrow their milk allergy, the investigators said.

Further analysis found that patients with persistent allergy had higher cow's milk IgE levels at all ages up to 16. The highest IgE for each patient, defined as peak cm-IgE, was found to be highly predictive of long-lasting outcome (P<0.001), the researchers said.

In addition, coexisting asthma (P<0.001) and allergic rhinitis (P<0.001) were also significant predictors of outcome, they reported.

Discussing the multiple criteria for establishing tolerance, and a possible study limitation, the researchers said that children who cannot pass a milk challenge may actually be tolerant.

The authors suggested that the poor prognosis in this study may result from the highly atopic referral population. Thus, they wrote, "other markers of the high degree of atopy in our population include 91% having at least one other food allergy, 49% with asthma, 40% with allergic rhinitis, and 71% with eczema."

However, it may also be that the character of milk allergy has changed over time, Dr. Wood said.

Similar trends were seen for 881 patients (68% male) in the egg-allergy study. When tolerance was defined with the most conservative criteria (egg IgE <2 kU/L), 4% outgrew their allergy by age four, 26% by age eight, 48% by age 12, and 68% by age 16.

Individuals with persistent egg allergy had higher antibody levels at all ages up to 18, the end of the period studied.

Egg allergy is generally considered to have a good prognosis, and parents are typically counseled that their children will outgrow it by early school age, the researchers said.

Indeed, this study supports the idea that a majority of atopic children with IgE-mediated egg allergy will develop tolerance -- but not by early school age as once thought.

Furthermore, an egg IgE level greater than 50 kU/L is a marker of persistent egg allergy, as well as the presence of other food allergy, and other atopic disease, they said.

A limitation of the egg study, the researchers wrote, is that many patients being evaluated for atopic dermatitis or other food allergies before egg was added to their diets were diagnosed on the basis of IgE alone and did not have a history of reaction to egg. However, Kaplan-Meier survival curves suggested that these children did in fact have a true egg allergy.

The researchers concluded that antibody tests are highly predictive of allergy outcomes and should be used in counseling patients on prognoses of egg or milk sensitivity. Because some patients do not develop tolerance until adolescence or later, follow-up and re-evaluation of these patients is important in their care.