Table 1

 Methodology of included studies (summary)

Reference (country)Case selectionControl selectionExposure measurementConfounding factors consideredSample sizeAge
Greco et al22 (Italy)Children with CD in Campania region, ItalyHealthy children from the same region.Interview by one of the authorsAge and area of residence, age at gluten introduction, father’s occupation201 cases, 1949 controlsCases, mean 2.14 years, SD, 2.6; controls, 2.34, SD, 2.93
Peters et al4 (Germany)From a CD incidence study and appeals at a national meeting.Identified through a population registryQuestionnaireAge, sex, number of inhabitants in area, FH of CD, age at gluten introduction143 cases, 137 controlsMean age 6.4 years (median 6.2)
Falth-Magnusson et al23 (Sweden)Children with CD in participating centresHealthy children living in the same region selected.QuestionnaireAge, area of residence72 cases, 264 controlsMedian age 3.1 years (range 1.4–5.1)
Ivarsson et al3 (Sweden)Children on CD databaseSelected through national population registerQuestionnaireAge, sex, area of residence, other infant feeding practices491 cases, 781 controlsAge range of participants was 0–14.9 years
Auricchio et al5 (Italy)Cases in participating centres who had healthy siblingsSiblings of cases without symptoms of CDInterviewNot specifically stated but by using sibling controls, some genetic, environmental and socioeconomic factors might have been controlled for216 cases, 289 controlsMedian age at diagnosis 15 months (range 6 months to 14 years).
Ascher et al6 (Sweden)Siblings of known CD patients found to have HLA genotype DQA1*0501-DQB1*02 and CD on screeningSiblings with the HLA genotype but who did not have CD on small intestinal biopsyInterviewControlled for HLA genotype and socioeconomic factors but not for age8 cases, 73 controlsMedian age 7.9 years for cases and 7.4 years for controls