Paediatrics (RCH) - Theses
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ItemThe epidemiology of egg allergy and other IgE-mediated food allergies in infants( 2010)IgE-mediated food allergy often develops early in life and has a major impact on the quality of life of the child and its family. Recent increases in the prevalence of food allergy, which have occurred too rapidly to be explained by genetic factors alone, suggest that environmental factors may play an important role. Potential candidates include maternal and infant diet and infant microbial exposures. However, few studies to date have examined risk factors for food allergies. I investigated the prevalence and risk factors for egg allergy, the most common IgE-mediated food allergy in infants, within the HealthNuts study. HealthNuts is an ongoing population-based cross-sectional study of 12-month-old infants in Melbourne, Australia. As part of the study, parents reported on infant feeding and other environmental exposures. All infants subsequently received a skin prick test for four foods including egg white and those with a wheal size ≥ 1mm underwent an oral food challenge with raw egg white. This thesis includes data from the first 2,600 infants included in the study, which is due to complete recruitment in April 2011. Among infants participating in the HealthNuts study, there was a high prevalence of egg allergy (9.3%, 95% CI 8.2-10.5). There was no evidence that maternal dietary factors were associated with infant egg allergy. Of the infant dietary factors examined, only timing of egg introduction was associated with egg allergy risk. Introduction of cooked egg into the infant diet at 4-6 months of age was associated with a 3-fold decreased risk of egg allergy compared with introduction after 12 months of age. Other infant dietary factors previously suggested to be associated with general allergy risk, namely duration of breastfeeding and age at introduction of first solid foods, were not associated with egg allergy. Factors previously associated with increased microbial exposure, including siblings, childcare and pet ownership, were associated with a reduced risk of egg allergy. There was evidence of a dose-response effect for siblings and egg allergy, with an increasing number of siblings associated with a further reduction in egg allergy: one sibling, OR0.72 (95% CI 0.53-0.97), two siblings OR 0.57 (95% CI 0.35-0.92) and three or more siblings OR 0.47 (95% CI 0.20-1.09). Attending childcare before 7 months of age was associated with a reduced risk of egg allergy compared with never having attended childcare (OR 2.05, 95% CI 0.97-4.35), while there was no evidence of a protective effect of childcare attendance between 7-12 months of age. Having either a cat or dog at home at one year of age was associated with a reduced risk of egg allergy among infants with a history of eczema (OR 0.49, 95% CI 0.31-0.78) but not among those without a history of eczema (OR 1.01, 95% CI 0.62-1.62). My results show that egg allergy is common in infants and suggest several possible risk factors related to infant diet and potentially microbial exposures which may help to explain recent rise in food allergy prevalence. The protective effect of introduction of egg at 4-6 months of age has implications for infant feeding guidelines internationally and, if confirmed, suggests that changes in infant feeding practices could have the potential to reduce the prevalence of egg allergy.