Environmental factors associated with allergy in urban and rural children from the South African Food Allergy (SAFFA) cohort

Abstract

Background: The prevalence of allergic diseases differs in urban and rural populations.

Objective: We sought to assess associations between environmental and dietary factors with allergic diseases in urban and rural South African children.

Methods: Toddlers aged 12 to 36 months were assessed for food allergen and aeroallergen sensitization, atopic dermatitis, allergic rhinitis, asthma, and challenge-proved 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 unpasteurized 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 were assessed. A subsection completed questions on consumption of fruits and 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 unpasteurized 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 cesarean 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 meats 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 cesarian section, and protective factors include consumption of fermented milk products. Modifiable risk factors urgently require interventions to prevent increasing allergy rates in countries undergoing rapid urbanization.

Keywords: Aeroallergen; Africa; advanced glycation end-products; aeroallergen sensitization; allergic rhinitis; antibiotics; antihelminthics; asthma; atopic dermatitis; cesarean section; cooking fuel; delivery mode; eczema; environmental exposures; farm animals; fast foods; food allergy; food sensitization; heating fuel; pets; prebiotics; prevalence; probiotics; rural; smoking; sunlight; unpasteurized milk; urban; urbanization.