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Objective: To determine the prevalence of sensitisation to peanuts and tree nuts in all children born during one year in one geographical area., Design: Birth cohort study with structured review at ages 1, 2, and 4 years., Setting: All children born on the Isle of Wight between January 1989 and February 1990., Subjects: Of 1456 children originally included, 1218 were reviewed at age 4 years. Of these, 1981 had skin prick tests., Main Outcome Measures: Positive skin test results, clinical atopic disease, and risk factors for the development of atopy., Results: 15 of 1218 (1.2%) children were sensitised to peanuts or tree nuts (13 to peanuts). Six had had allergic reactions to peanuts (0.5% of the population), one to hazelnuts, and one to cashew nuts; three had had anaphylactic reactions. Seven children had positive skin test results or detectable IgE to peanuts without clinical symptoms. Two children who reacted to peanut in infancy had lost their sensitivity by 4 years. Family history of atopy, allergy to egg (odds ratio 9.9, 95% confidence interval 2.1 to 47.9, and eczema (7.3, 2.1 to 26.1) were important predictors for peanut allergy., Conclusions: IgE mediated allergy to peanuts is common in early childhood. In many the allergy persists but a minority may develop tolerance.

Few authorities doubt that here has been a significant rise in IgE mediated diseases in almost all populations in which they have been studied. There is less agreement why this should have occurred and a number of genetic and environmental influences almost certainly play a part. Although the present discussions are concentrating on dietary factors these cannot be expected to play more than a partial role in the pathogenesis and expression allergy. The approach to the prevention of allergy, generally implying IgE mediated disease, has been described as primary, secondary or tertiary. Primary prevention means prevention of sensitisation, secondary prevention means prevention of manifestation of disease in an already sensitised individual, and tertiary means attempting to reduce or abolish expression of allergy in an individual already showing symptoms. Such as classification is convenient although the borders become blurred. It had until recently been assumed that sensitisation rarely if ever took place before birth. Recent studies from Melbourne (Tang et al., 1994), Southampton (Warner JA et al., 1994) and Japan (Kondo et al., 1992) suggest this may no be so. Their studies have given evidence of intrauterine programming. Warner showed a raised peripheral blood mononuclear proliferative response in infants born to atopic families in those who developed atopic eczema with positive skin prick test to foods. The Melbourne group has recently shown a reduced IFN-chi in cord blood mononuclear cells from infants of atopic families. Thus previous attempts at primary prevention may indeed be secondary prevention as immune responses are already developed at birth. Additionally it may be necessary to move attempts at intervention back into early pregnancy or even pre-conception. This would compound the problems of an already difficult area of preventive medicine.

Background: One hundred twenty children, identified before birth as being at high risk for atopy, were prenatally assigned to prophylactic or control groups., Methods: The infants in the prophylactic group either received breast milk from mothers on an exclusion diet or an extensively hydrolyzed formula. Their bedrooms and living rooms were treated repeatedly with an acaricide, and they used polyvinyl-covered mattresses with vented head areas. The infants in the control group were fed conventionally, and no environmental control was recommended., Results: A significant advantage, first demonstrated at 1 year of age, persists for children in the prophylactic group. They have less of any allergy or eczema, but the reduced prevalence of asthma is no longer significant. Only three children in the prophylactic group had positive skin prick test results compared with 16 in the control group, suggesting a significant reduction in sensitization., Conclusion: A dual approach to allergen avoidance, focusing on foods and aeroallergens, appears to be beneficial in selected high-risk infants. Avoidance of potent allergens in early life increases the threshold for sensitization in these high-risk infants. Whether sensitization has been avoided or merely deferred has yet to be proved.