Epidemiology of food hypersensitivity in schoolchildren Validation with double-blind placebo-controlled food challenges and biomarkers

Abstract: Background: This thesis focuses on the incidence and remission of reported food hypersensitivity in schoolchildren followed from 8 to 12 -years of age and the prevalence of hypersensitivity to milk, egg, cod and wheat among 12-year olds investigated by reported data, clinical investigation and double-blind placebo-controlled food challenges and biomarkers.Methods: The studies are mainly based on a population based cohort recruited in 2006 from three municipalities in Northern Sweden. All children in first and second grade, aged 7-8 years, were invited to a parental questionnaire study and 2585 (96% of invited) participated. The children in two of the municipalities were also invited to a skin prick test with airborne allergens. At age 11-12 years, there was a follow-up of the cohort using the same methods, with the addition of a child interview and assessment of body mass index (BMI).At the follow-up, children who reported milk hypersensitivity were invited to structured interviews and children reporting complete elimination of milk, egg, cod or wheat due to perceived hypersensitivity were invited to a clinical examination and blood sampling. According to test results, the children were categorized into different food hypersensitivity phenotypes according to preset criteria. Children categorized as current food allergy were then invited to further evaluation with a double-blind placebo-controlled food-challenge using newly developed recipes. Before their use, the recipes were successfully validated regarding detectable sensorial differences between the active and placebo substances in a separate cohort of healthy schoolchildren (n=275).Before and after the challenge series blood samples were collected for analyses of cytokine mRNA expression in peripheral blood mononuclear cells including hallmark cytokines for the humoral allergy-promoting T helper (Th) 2 response, cellular cytotoxicity-promoting Th1 response, inflammatory-, and T regulatory responses. Fecal inflammatory biomarkers were also analyzed before and after the challenge series.Results: Reported food hypersensitivity increased from 21% at age 7-8 years to 26% at 11-12 years. There was a high incidence (15%) as well as a high remission (33%) of reported food hypersensitivity. Risk factors associated with incidence and remission were different for milk hypersensitivity and hypersensitivity to foods other than milk. The agreement between reported symptoms to milk, egg, cod, wheat, soy and peanut and sensitization to the culprit food was poor. At 11 to 12-years of age the prevalence of reported allergy to milk, egg, cod or wheat was 4.8% while the allergy prevalence according to clinical evaluation was 1.4%. This figure was further halved when evaluated with double-blind placebo-controlled food challenges.The majority of children with reported allergy to milk, egg, cod and wheat were categorized as other food hypersensitivity phenotypes, the most common being probable lactose intolerance (40%) and outgrown food allergy (19%). Even though reported milk hypersensitivity among the 11-12 year olds was 14.5%, only 3% were categorized as current milk allergy. Current and outgrown milk allergy was associated with other atopic disorders and a lower BMI (OR 0.8, 95% CI 0.80-0.98). Before the challenge series, the mRNA expression of the cytokines IL-13 and IL-10 were higher among children with a positive compared to a negative challenge outcome.Conclusion: Reported food hypersensitivity was common among school children in Northern Sweden and increased from 7-8 years to 11-12 years of age, and both the incidence and remission of reported hypersensitivity was high. There was an 8-fold difference in the prevalence of allergy to milk, egg, cod or wheat when reported data was assessed by clinical examinations and double-blind placebo-controlled food challenges. Allergy to milk, egg, cod and wheat was an uncommon cause of complete avoidance of these foods due to perceived hypersensitivity. Some of the analyzed biomarkers might serve as prognostic markers for symptomatic, IgE-mediated food allergy but need further validation.