Study population
The study population was derived from the prospective population-based Type 1 Diabetes Prediction and Prevention (DIPP) birth-cohort study described in detail previously 22. Briefly, children born in the Tampere, Turku, and Oulu University Hospitals in Finland are screened at birth for HLA genotypes conferring to increased risk of type 1 diabetes. Written informed consent was obtained from caretakers both for HLA screening and follow-up. The study protocol was approved by the ethics committees of the participating hospitals. The present study included children born between years 1995 and 2004 in Tampere and Oulu where children carrying the HLA-DQB1 genotypes *02/*0302 and *0302/x (x ≠*02), *0301 or *0602 were invited to follow-up. Blood samples were drawn at 3, 6, 12, 18, and 24 months of age and once a year thereafter. Atopic case and non-atopic control subjects were identified among children with an available serum sample for both EV antibody assay (serum sample between 1 and 5 years of age) and s-IgE antibody assay (serum sample at 5 years of age). Altogether 138 case children with a positive s-IgE test and 138 matched control children with negative s-IgE test were identified. Of the 138 case children 65% were sensitized to the food allergen mixture and 71% to the inhalant allergen mixture. Of those positive for foods 57% tested positive for cow’s milk, 32% for egg, 22% for wheat, and 6% for fish. Of those positive for inhalants 57% were positive for birch, 37% for timothy, 3 % for cat, and 10% for house dust mite. The pairs were matched by gender and age at the EV antibody measurement (+/- 3 months). The proportion of boys was 65%.
Allergic diseases were identified at 5 years of age by ISAAC questionnaire questions: “Has your child ever had asthma/hay fever or some other allergic rhinitis/atopic eczema diagnosed by a doctor?”. ISAAC-data was missing in 39 children. Their allergic disease diagnoses were retrieved from the DIPP database: atopic dermatitis (ICD-code L20.x), asthma (J45.x) and allergic rhinitis/hay fever (J30.x) reported and confirmed by a physician by 5 years of age. Sixty-four (46%) out of the 138 IgE-sensitized case children reported an allergic disease (47 atopic dermatitis, 27 allergic rhinitis and 15 asthma) and formed a case subgroup for analysis of enteroviruses’ association with clinical disease. These 64 case children were compared to their IgE-negative matched control children. Some of the 64 IgE-negative control children also reported an allergic disease (n = 17), but were eligible as controls, as IgE sensitization was the feature defining case vs. control status. Thirty-one (22.5%) out of the total of 138 IgE-negative control children reported an atopic disease (25 atopic dermatitis, 2 allergic rhinitis and 8 asthma reports).
Background data of the participants retrieved from the DIPP database included information of the age at the entry of daycare, duration of breastfeeding, level of maternal and paternal education, HLA-DQB1-genotype, the presence of type 1 diabetes associated islet autoantibodies, pets at home, older siblings and maternal smoking during pregnancy. Parental atopy background information was available in the ISAAC-data for all but 39 children. Maternal smoking was excluded from the analyses as it was reported by only five mothers.