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Tuesday, June 1, 2010

Tracking peanut and tree nut allergy in the US

Peanut and tree nut allergies garner attention because reactions to these common foods are characteristically severe, are responsible for the majority of fatalities caused by food allergy, are persistent, and appear to be increasing in prevalence. Although there is great interest in tracking the prevalence of these allergies, determining the exact number of those affected over time has remained elusive.

To estimate the general population prevalence of food allergies, researchers have sometimes had to content themselves with assessments based on self-report of “convincing” reactions, because the diagnostic standard of oral challenge is impractical, risky, and expensive. Using this approach, Sicherer et al (J Allergy Clin Immunol 2010;125:1322-6) report findings of the most recent cross-sectional telephone survey to collect self-reported information on peanut, tree nut, and, additionally, sesame allergy. They employed the same survey used in 1997 and 2002 to assess prevalence in 2008, then compared the results from all three surveys.

Significant increases in peanut/tree nut and tree nut allergy in children were reported from 2002 to 2008, though increase in peanut allergy was not significant in that period. Self-reported peanut allergy in children increased significantly from 0.4% in 1997 to 1.4% in 2008. Tree nut allergy also showed significant increased from 0.2% to 1.1% across the same period. Sesame allergy was reported from only 13 survey participants at a rate of 0.1%; however, 2008 was the first year that information on sesame allergy was collected. The authors report that no significant increase in peanut and/or tree nut allergy was reported in adults.

They suggest that possible explanations for the increased rate of self-reported peanut allergy might be increased availability of peanuts in many food products, especially in highly allergenic roasted form, as well as oral exposure that is either immunologically too early or late, and/or environmental exposure. Also, Sicherer et al. point out that the prevalence in US children is similar to the prevalence reported by recent studies in Canada, the UK, and Australia.

We asked lead author Scott Sicherer, MD, from Mount Sinai School of Medicine, to comment on the study. “To my knowledge, this is the first attempt to track these allergies on a population basis in the US using the same methods thrice over a decade,” says Sicherer. “A recent review of the food allergy literature in JAMA [Journal of the American Medical Association] pointed out that due to various methodological issues, we do not have solid data on prevalence, with estimates that food allergy affects more than 1-2% but less than 10% of the population and there are limited data on time trends. Although our study has limitations inherent to self reported allergy and participation rates of telephone surveys, it provides an interesting perspective supporting a likely increase of childhood peanut/tree nut allergies and underscores that millions are affected by these allergies.”

Readers interested in this topic might also want to see the article by Ben-Shoshan et al., also in the June issue (J Allergy Clin Immunol 2010;125: 1327-1335), which looks at prevalence of peanut, tree nut, fish, shellfish, and sesame allergies in Canada.

We want to hear from you. Please feel free to post your questions or comments below. All questions and comments will be forwarded to the authors for a response.

Exactly how can specific IgE levels help in the diagnosis of food allergy?

An important question for researchers and clinicians who work with food allergies is whether food-specific IgE and skin prick test results can be used reliably as ersatz measures of allergen sensitization (see also our News Beyond Our Pages blog from May 14). The reason is that the clinical standard for food allergy diagnoses is double-blind, placebo-controlled food challenge, which is expensive, costly, and requires dedicated personnel and facilities because of the risk of anaphylaxis.

In a Letter to the Editor in JACI (J Allergy Clin Immunol 2010;125:1391-2), van Nieuwaal et al. report results from a study conducted in 103 children with suspected peanut allergy. Peanut-specific IgE levels were correlated to results of diagnostic food challenge to evaluate the predictive power of specific IgE and food challenges were performed regardless of a possible history of anaphylaxis. The population was very atopic as well, with greater than 80% having atopic dermatitis. The authors report that peanut-specific IgE was correlated to positive food challenge results in approximately 55% of the children. Specificity of IgE values of 10.4 [92%], 24.8 [98%] and 25.5 kU/L [100%] were significant for predicting outcome of food challenge. The authors note that the specific IgE levels were not sensitive, though, and that values lower than these do not indicate that there would be no reaction to oral food challenge.

The authors conclude that using these IgE levels as cutoffs would obviate diagnostic oral food challenges in at least some of the children. Oral food challenge would still be needed to determine the sensitivity and severity of the peanut allergy.

We want to hear from you. Please feel free to post your own questions or comments. All questions and comments will be forwarded to the authors for a response.