In February 2013, we kicked off the South African Food sensitisation and Food Allergy (SAFFA) study based in the Paediatric Allergy Department at Red Cross Children’s Hospital (UCT). After Professor Claudia Gray’s work showed unexpectedly high rates of food allergy in children with eczema we were wondering how common food allergy really was in the general population. Our impression in the Allergy Clinic was that it was rising and more common than previously thought. If true, we would be following a similar path as other countries where food allergy rates have been rising rapidly over the last decades. However, there was no existing South African data to support or refute this observation.
We also wanted to know more about the probable causes for the rise in food allergy that has been described worldwide. These include many changes in the modern environment and diet that are associated with industrialisation and urbanisation.
Therefore in addition to screening 1200 children in urban Cape Town, we also screened 400 children in the deeply rural Eastern Cape so that we could compare them to urbanised children who live in Cape Town in very different environments. These were all healthy children attending randomly selected registered Early Childhood Development centres across the Cape Town metropole or recruited in community drives and screened at community health centres in the Mqanduli district of the Eastern Cape.
All participating children were screened for food allergy by doing skin prick tests for the 7 commonest food allergens in children (egg white, peanut, cow’s milk, fish, soya, wheat and tree nuts). Parents completed a comprehensive questionnaire detailing weaning practices, family histories and environmental and dietary exposures. In the children who had a reactive skin prick test result and who were not clearly tolerating a particular food in their regular diet, we confirmed or refuted the diagnosis of food allergy by doing an oral food challenge to the suspected food.
We found that 2.5% of 1 to 3-year-old children in Cape Town had a challenge confirmed food allergy, most commonly to egg (1.9%), some to peanut (0.8%) and very few to milk and fish (0.1%).
There were no significant differences in food allergy rates between children of different ethnicities with 2.9% of urban Black African children having a food allergy.
In the rural Eastern Cape however only 0.5% of children had a confirmed food allergy. These were all Black African.
These results show that the urban food allergy prevalence in Cape Town is comparable to rates in other middle-income countries and rapidly urbanising communities. It also shows a significantly lower rate of food allergy in rural South African children and furthermore provide convincing evidence that urban vs rural differences are more crucial factors than ethnicity in the development of food allergies.
This is the first population based study of food allergies in South Africa. Our work is not done though, and we are continuing further analysis of the large amount of data that we have collected. We will now be able to look in more detail at the weaning histories, migration histories and other environmental factors such as cigarette smoke exposure, pet ownership, contact with farm animals etc. In a small sub-cohort, we are also looking at stool and skin microbiome, parasite infestations and house dust components to gain more insights into how urban and rural environments differ and how they may influence the development of allergies.