Medscape Article

From Current Opinion in Allergy and Clinical Immunology

Peanut, Tree Nut and Seed Allergies
Posted 05/21/2004

Suzanne S. Teuber; Kirsten Beyer

Introduction
In the past year, there have been significant advances in our overall knowledge base concerning peanut, tree nut and seed food allergies. These plant foods share the unfortunate distinction of association with a persistent food-allergic state in the majority of individuals affected. Further information on peanut and tree nut allergens, cross-reactivity and data on sesame, sunflower or other seed allergies are still sorely needed. In spite of increasing knowledge and public awareness of food allergies - including the shift away from early (on purpose) introduction of peanut in the diet and the favorable trend towards increased breastfeeding - serious food allergy continues to develop, indicating the potential for research and discovery in the area of primary sensitization and tolerance towards environmental and food proteins. Herein, we will review a few of the recent reports on peanut, tree nut and seed allergies.

Epidemiology
Studies continue to suggest an increase in the prevalence of clinical peanut allergy among children - this is alarming because the follow-up periods between similar surveys have been as short as 5 years.[1,2**] Sicherer and colleagues[3] conducted a second random digit dial telephone survey 5 years after the original study and determined the self-reported prevalence of peanut or tree nut allergy in combined adults and children to be 1.4%. In the most recent 2002 survey, the overall prevalence in the general population was similar for peanut and tree nut allergy at 1.04% but, significantly, the rate of reported clinical reactivity to peanuts among children was doubled in this second survey, from 0.4% to 0.8% (P=0.05). Among the tree nut allergies reported, walnut was again the most common, followed by cashew and almond.[2**]

In Montreal, Kagan et al.[4**] administered questionnaires to families of 7768 children, ranging from kindergarten to third grade, at randomly selected elementary school sites, with 4339 families choosing to participate. The study went further than the random digit dial telephone surveys in that the histories were corroborated with skin prick testing, and in those with uncertain histories with a positive skin prick test, quantification of specific IgE followed by oral peanut food challenges (if the specific IgE level was less than 15 kU/l) were performed. Using these diagnostic criteria, a surprisingly high prevalence of peanut allergy was suggested in this population (1.34%).

A factor that is postulated to have contributed to peanut allergy in the UK is the cutaneous exposure to ultra-low doses of peanut antigens in peanut oil found in diaper rash creams and emollients which have been applied to the skin of infants with eczema or diaper rash. Lack et al.[5] took advantage of the unique opportunity afforded by a geographic cohort study, the Avon Longitudinal Study of Parents and Children, to prospectively gather detailed information related to the development of peanut allergy. The data on skin emollients were obtained in a retrospective telephone interview. Peanut allergy was reported in 49 of 13 973 children (0.4%) born in 1991-92 and 36 were available to undergo skin testing at age 4-6 years old. Twenty-nine had positive skin tests and 23 had positive double-blind, placebo-controlled food challenges to peanut. Multivariate logistic regression revealed the aforementioned association with topical peanut oil in emollients and also with a family history of peanut allergy, the presence of oozing, crusted rash and, to a lesser extent, the consumption of soy formulas. We do not know if peanut oil has been included in diaper rash creams and emollients in Canada, but it is not contained in the main brands used in the USA; other associations should obviously be explored, but the findings are intriguing.

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Section 1 of 4 Next Page: Allergens

Suzanne S. Teubera and Kirsten Beyerb

aDivision of Rheumatology, Allergy and Clinical Immunology, University of California, Davis, California, USA and bDepartment of Pneumology and Immunology, University Children's Hospital Charit