F Ood Allergy in S Outh a Frica : Joining the Food Allergy Epidemic ?
نویسنده
چکیده
The last 10-15 years have seen a steep rise in food allergies in westernised countries. South Africans, especially those of black descent, have traditionally enjoyed a low rate of food allergy and have long been thought to be protected against the food allergy epidemic. Previous food allergy prevalence studies in South Africa have focused on sensitisation and questionnaires which are not a true reflection of clinically relevant food allergy. A recent food allergy prevalence study in eczematous patients in Cape Town has shown a surprisingly high rate of challengeproven food allergies in children of both Xhosa and mixed descent. These findings suggest that South Africa may not be spared from the food allergy epidemic. A large study investigating the prevalence of food allergy in an unselected group of young children is currently being planned, focusing on differences between urban and rural areas and between ethnic groups. Various factors which may contribute to the expression or suppression of food allergy, including exposure to foods, genetics, infections, diet and intestinal microbiota need further study. A better understanding of factors contributing towards food allergy expression will help us to define preventative strategies to curb the rise in food allergy. Correspondence: Dr Claudia Gray, e-mail [email protected] Claudia Gray, MB ChB, MRCPCH, MScClin Pharm, DipAllergy, DipPaedNutrition Allergy and Asthma Clinic, Red Cross Children’s Hospital, Cape Town, and private practice, Vincent Palotti Hospital, Cape Town, South Africa Shiang-Ju Kung, MB BCh, DCH, FAAP University of Botswana, Gaborone, Botswana; Division of Allergy & Immunology, Children’s Hospital of Philadelphia, USA BACKGROUND There is increasing evidence of a rise in the prevalence of food allergy, dubbed the ‘second wave’ of the allergy epidemic. Enigmatically the food allergy epidemic has lagged behind the initial rise in respiratory allergies by several decades. This rise in food allergies has been described mostly in westernised countries by phenomenal statistics such as a two-fold rise in peanut allergy in the UK over the last 10-15 years. A recent review also showed the incidence of challenge-proven food allergy in 10% of young children in Australia. The importance of food allergies in westernised countries has received much recognition by large epidemiological studies such as the EuroPrevall study looking at food allergy and its impact in European countries. Interestingly, peanut allergy in the UK seems to have stabilised, implying that food allergy prevalence may already have peaked in certain parts of the world. In South Africa, evidence suggests a significant increase in respiratory allergies, which mirrors the pattern described in westernised countries, albeit lagging behind. However, there is a dearth of studies looking at food allergies in South Africa, as with the entire African continent. In the handful that have been performed, data reflect sensitisation or questionnaire-based allergies, both of which notoriously overestimate true allergy. Moreover, previous studies have lacked uniformity in the definition and diagnosis of food allergy, making it difficult to extrapolate the true allergy prevalence. In particular, there are few data on children younger than 3 years, the population with the lifetime peak prevalence of food allergy. Anecdotally, true food allergy is deemed to be rare in South Africa, especially in the black African population. However, South Africa is an ethnically diverse nation, with differences between ethnic groups in allergy expression. Moreover, the indigenous black population is rapidly urbanising and taking on a new ‘westernised’ diet and lifestyle. This may have an effect on prevalence of food allergy. Recent studies indicate that food allergies may be gaining more prominence across ethnic groups in South Africa, as will be discussed in this article. This could become a major health burden at an individual and public level. DIFFICULTIES IN DIAGNOSING FOOD ALLERGY Before describing food allergy studies in South Africa, the diagnostic challenges in food allergy prevalence studies deserve mention. Worldwide, the marked heterogeneity in food allergy prevalence reflects different diagnostic methodology and definitions of allergy. A major pitfall is that sensitisation does not equate to allergy. This may be of particular significance in the black African population. Some of the inherent difficulties in diagnostic tests are mentioned briefly below: Skin-prick testing (SPT): not only is this operatordependent, but racial differences in skin thickness and reactivity to histamine may influence outcomes. The source of the allergen extracts may also influence results since these may not represent local allergens. Food-specific IgE (sIgE): South Africa has a high prevalence of helminth infections, which may strongly amplify the IgE response and can lead to false elevation of specific IgE levels. Cross-reactivity between components of food allergens and environmental allergens are increasingly recognised. An example is grass pollen cross-reacting with cereals, soya and peanut by a specific IgE to similar carbohydrate determinants. Interpreting a specific IgE level for food without considering cross-reactivity can lead to false positives for true food allergy. This is an important consideration since aeroallergen sensitivity has increased significantly in South Africa in the last few decades. Component resolved diagnostics has refined the art of cross-reactivity recognition, but high cost and poor availability make it prohibitive in many parts of South Africa. 95% positive predictive value cut-off levels for skin-prick tests and specific IgE are still commonly
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تاریخ انتشار 2012