Browsing by Author "Williams HC"

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    Are Environmental Factors for Atopic Eczema in ISAAC Phase Three due to Reverse Causation?
    (Elsevier, Inc. on behalf of the Society for Investigative Dermatology, 2019-05) Rutter CE; Silverwood RJ; Williams HC; Ellwood P; Asher I; Garcia-Marcos L; Strachan DP; Pearce N; Langan SM; ISAAC Phase Three Study Group
    Some previously described environmental associations for atopic eczema may be due to reverse causation. We explored the role of reverse causation by comparing individual- and school-level results for multiple atopic eczema risk factors. The International Study of Asthma and Allergies in Childhood (i.e, ISAAC) Phase Three surveyed children in schools (the sampling unit) regarding atopic eczema symptoms and potential risk factors. We assessed the effect of these risk factors on atopic eczema symptoms using mixed-effect logistic regression models, first with individual-level exposure data and second with school-level exposure prevalence. Overall, 546,348 children from 53 countries were included. At ages 6-7 years, the strongest individual-level associations were with current paracetamol use (odds ratio [OR] = 1.45, 95% confidence interval [CI] = 1.37-1.54), which persisted at school-level (OR = 1.55, 95% CI = 1.10-2.21), early-life antibiotics (OR = 1.41, 95% CI = 1.34-1.48), and early-life paracetamol use (OR = 1.28, 95% CI = 1.21-1.36), with the former persisting at the school level, whereas the latter was no longer observed (OR = 1.35, 95% CI = 1.00-1.82 and OR = 0.94, 95% CI = 0.69-1.28, respectively). At ages 13-14 years, the strongest associations at the individual level were with current paracetamol use (OR = 1.57, 95% CI = 1.51-1.63) and open-fire cooking (OR = 1.46, 95% CI = 1.33-1.62); both were stronger at the school level (OR = 2.57, 95% CI = 1.84-3.59 and OR = 2.38, 95% CI = 1.52-3.73, respectively). Association with exposure to heavy traffic (OR = 1.31, 95% CI = 1.27-1.36) also persisted at the school level (OR = 1.40, 95% CI = 1.07-1.82). Most individual- and school-level effects were consistent, tending to exclude reverse causation.
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    Siblings, asthma, rhinoconjunctivitis and eczema: a worldwide perspective from the International Study of Asthma and Allergies in Childhood.
    (WILEY-BLACKWELL, 2015-01) Strachan DP; Aït-Khaled N; Foliaki S; Mallol J; Odhiambo J; Pearce N; Williams HC; ISAAC Phase Three Study Group
    BACKGROUND: Associations of larger families with lower prevalences of hay fever, eczema and objective markers of allergic sensitization have been found fairly consistently in affluent countries, but little is known about these relationships in less affluent countries. METHODS: Questionnaire data for 210,200 children aged 6-7 years from 31 countries, and 337,226 children aged 13-14 years from 52 countries, were collected by Phase Three of the International Study of Asthma and Allergies in Childhood (ISAAC). Associations of disease symptoms and labels of asthma, rhinoconjunctivitis and eczema were analysed by numbers of total, older and younger siblings, using mixed (multi-level) logistic regression models to adjust for individual covariates and at the centre level for region, language and national affluence. RESULTS: In both age groups, inverse trends (P < 0.0001) were observed for reported 'hay fever ever' and 'eczema ever' with increasing numbers of total siblings, and more specifically older siblings. These inverse associations were significantly (P < 0.005) stronger in more affluent countries. In contrast, symptoms of severe asthma and severe eczema were positively associated (P < 0.0001) with total sibship size in both age groups. These associations with disease severity were largely independent of position within the sibship and national GNI per capita. CONCLUSIONS: These global findings on sibship size and childhood asthma, rhinoconjunctivitis and eczema suggest at least two distinct trends. Inverse associations with older siblings (observations which prompted the 'hygiene hypothesis' for allergic disease) are mainly a phenomenon of more affluent countries, whereas greater severity of symptoms in larger families is globally more widespread.