Environmental factors associated with allergy in urban and rural children from the South AFrican Food Allergy (SAFFA) cohort.
BACKGROUND The prevalence of allergic diseases differs in urban and rural populations. OBJECTIVE To assess associations between environmental and dietary factors with allergic diseases in urban and rural South African children. METHODS Toddlers aged 12 36 months were assessed for food and aero allergen sensitisation, atopic dermatitis, allergic rhinitis, asthma and challenge proven food allergy. Information was collected on family history of allergic diseases, household size, socioeconomic status, delivery mode, antibiotic and probiotic use, exposure to fermented and unpasteurised milk, antihelminth treatment, sunlight exposure, pet and farm animal exposure, cigarette smoke and household cooking and heating fuels. Antenatal exposures to pets, livestock and cigarette smoke was assessed. A subsection completed questions on consumption of fruit/vegetables, fast foods, soft drinks/fruit juices and fried/microwaved meat. RESULTS Risk and protective factors differed between urban and rural settings. Exposure to farm animals in infants and their mothers during pregnancy was protective against allergic outcomes in the rural population. Consumption of unpasteurised milk is uncommon in this group of rural children and is unlikely to be an important factor in rural protection. In urban children birth by caesarean section is associated with food allergy and consumption of fermented milk products is associated with reduced asthma and atopic dermatitis. In both cohorts antenatal maternal smoking and environmental smoking exposure were predominantly associated with asthma and consumption of fast foods and fried meat were associated with allergy. CONCLUSION In this rural environment exposure to livestock is the strongest protective factor. In urban communities, where animal contact is rare, risk factors include caesarian section and protective factors include consumption of fermented milk products. Modifiable risk factors urgently require interventions to prevent increasing allergies in countries undergoing rapid urbanization.
The Journal of allergy and clinical immunology