The GABRIEL Advanced Surveys: study design, participation and evaluation of bias

Abstract

Exposure to farming environments has been shown to protect substantially against asthma and atopic disease across Europe and in other parts of the world. The GABRIEL Advanced Surveys (GABRIELA) were conducted to determine factors in farming environments which are fundamental to protecting against asthma and atopic disease. The GABRIEL Advanced Surveys have a multi-phase stratified design. In a first-screening phase, a comprehensive population-based survey was conducted to assess the prevalence of exposure to farming environments and of asthma and atopic diseases (n = 103,219). The second phase was designed to ascertain detailed exposure to farming environments and to collect biomaterial and environmental samples in a stratified random sample of phase 1 participants (n = 15,255). A third phase was carried out in a further stratified sample only in Bavaria, southern Germany, aiming at in-depth respiratory disease and exposure assessment including extensive environmental sampling (n = 895). Participation rates in phase 1 were around 60% but only about half of the participating study population consented to further study modules in phase 2. We found that consenting behaviour was related to familial allergies, high parental education, wheeze, doctor diagnosed asthma and rhinoconjunctivitis, and to a lesser extent to exposure to farming environments. The association of exposure to farm environments with asthma or rhinoconjunctivitis was not biased by participation or consenting behaviour. The GABRIEL Advanced Surveys are one of the largest studies to shed light on the protective 'farm effect' on asthma and atopic disease. Bias with regard to the main study question was able to be ruled out by representativeness and high participation rates in phases 2 and 3. The GABRIEL Advanced Surveys have created extensive collections of questionnaire data, biomaterial and environmental samples promising new insights into this area of research.

Farming environments and childhood atopy, wheeze, lung function, and exhaled nitric oxide

“…1,3,4,15,19 As with atopy, the inverse association with the degree of atopic sensitization might be related to the effect of farm exposures on immune response. Despite the recent finding that microbial diversity seems to play a lesser role for atopy than for asthma, 2 farms provide an environment that can be seen as a model of natural immunotherapy.…”

“…The study design is further described in more detail elsewhere. 15 During phase 1 in 2006, 34,491 children 6 to 12 years old were recruited in rural areas of Austria, southern Germany, and Switzerland. A short questionnaire assessed asthma or allergic diseases and farm exposures.…”

The protective effect of farm milk consumption on childhood asthma and atopy: The GABRIELA study

“…Three exclusive disease strata were defined within each exposure stratum: (1) asthma, (2) atopy but no asthma, and (3) no asthma and no atopy. Of the 1903 eligible Bavarian children, 895 were selected by applying disproportionate stratified random sampling to create equally sized samples within each of the 9 strata (the study design is described in more detail elsewhere 11 ). Milk samples of 800 subjects were analyzed.…”

“…The GABRIEL (a multidisciplinary study to identify the genetic and environmental causes of asthma in the European Community) Advanced studies program, 11 comprising a large population of European children, was established to investigate the environmental Abbreviations used ALP: Alkaline phosphatase aOR: Adjusted odds ratio causes of asthma and atopy and includes data on analytically determined milk constituents. The aim of the present analysis was to find biological components of cow's milk that might explain the protective effect of farm milk on childhood asthma and atopy.…”

Protection from childhood asthma and allergy in Alpine farm environments—the GABRIEL Advanced Studies

“…5 Because of differences in study design, the Polish data will be reported separately. In the population-based phase I study a short recruiting questionnaire was distributed to parents of all schoolchildren through their elementary schools.…”