Food Allergy & Anaphylaxis in Asia
Over the past few decades there have been a global increase in asthma, allergic rhinitis and atopic dermatitis, followed by a rapid rise in food allergy, the so called “second wave of the allergy epidemic”. The prevalence and pattern of specific food allergies and food-induced anaphylaxis are quite distinct in Asia compared to that of the Western world. Even within Asia, population studies indicate that the prevalence of food allergy also differs between each country. The overall prevalence of food allergy in pre-schoolers was only 1% in Thailand , but as high as 5.3% in Korean infants  and 3.8% and 7.7% in one- to two-year-old children in China respectively. [3-4]
Food allergens differ by age group
Causative allergens for food allergy differ by age group across Asian countries. In general, cow’s milk and egg allergies were most prevalent in young children below 2 years of age in most Asian countries. [5-7] The prevalence of self-reported cow’s milk and egg allergies in 1-year-old children in Singapore was 0.4% and 1.8% respectively. In population-based studies from Thailand, cow’s milk, egg and shrimp allergies were commonly reported in the pediatric age group. [1, 8] In a large-scale epidemiological survey in Japan, the most frequent food allergens in Japanese children were hen's egg, cow's milk and wheat, accounting for 72.5% of all food allergy cases. [9-10] The three major causative foods in the <1-year-old age group were hen’s egg, cow’s milk and wheat, while crustaceans, wheat, fruits and peanut allergies were seen in the older age groups. 
In the older age groups, wheat/buckwheat allergies or shellfish predominated, depending on the country. [7, 12] Shellfish allergy is more common in older children and adults in South-East Asian countries such as Singapore, Philippines and Vietnam. The prevalence of self-reported shellfish allergy in Singapore was 1.19% in 4-6-year olds but 5.23% in 14-16-year-old school children.  In Singapore, it is also the commonest food allergen in adults.  Mirroring the situation in Singapore, a population-based survey in the Philippines reported that shellfish allergy (5.12%) was the most common self-reported food allergy in 14-16 year old school children.  In a population-based survey in Vietnam, shellfish allergy (2.6%) was the most common food allergy reported in adults, followed by beef allergy (0.8%), milk (0.2 – 0.7%) and egg (0.4%).  Shellfish is the most common cause of anaphylaxis in adolescents and adults in Singapore and Hong Kong. [15-18] It is also one of the most common causes of food-induced anaphylaxis in both children and adults in Thailand. [19-21]
Wheat allergy is particularly prominent in Japan, Korea and Thailand. In Japanese school children,  wheat allergy is more common than shellfish and nuts, and is the main cause of food-anaphylaxis in both Japan and Korea.  In Japanese adults, the prevalence of wheat allergy confirmed by skin prick test and serum ω-5 gliadin-specific IgE test is 0.21%.  An outbreak of new-onset IgE-mediated wheat protein allergy and wheat-dependent exercise-induced anaphylaxis (WDEIA) was also recently reported in previously healthy Japanese adults after exposure to hydrolyzed wheat protein in facial soap on intact facial skin, [24-26] highlighting the role of epicutaneous sensitization in the pathogenesis of food allergy in this population.
More recently, the prevalence of wheat allergy in Thailand has been on the rise, and wheat induced anaphylaxis in Bangkok, Thailand was reported in a few children.  Although the precise reasons for this disparity in the prevalence of wheat allergy in the Asian region are not known, one possible postulation may be related to methods of cooking and household exposure to wheat. Wheat flour in its form may be used more often in Japanese and Korean cooking, for example, dry flour is used in dishes such as tempura. 
The prevalence of food allergy & anaphylaxis appear to be increasing in Asia. The prevalence of challenge-proven food allergy in 1 to 2-year-old children in Chongqing, China, assessed using exactly the same study design 10 years apart, increased from 3% to 7% in just 10 years.  Wang et al. described a change from mainly drug-induced anaphylaxis in Hong Kong paediatric Emergency Department presentations in 2001 to predominantly food-induced anaphylaxis in 2015.  The top food anaphylaxis trigger in Singapore in the 1990s was bird’s nest,29 but this has since been superseded by peanut and seafood over the past decade. [15, 17, 30]
Other Unique Allergens in Asia
Galacto-oligosaccharide (GOS) allergy
Galacto-oligosaccharides are carbohydrates added to commercially available food products and beverages as prebiotics for the promotion of gut health. Allergic reactions were first reported in Japanese oyster shuckers who developed anaphylaxis after consumption of GOS-supplemented lactic acid beverages.  This was later shown to be result from cross reactivity of GOS with the Hoya antigen derived the sea squirts present on oyster shells.  Similar reactions were also reported in cow’s milk-tolerant children in Vietnam and Singapore after consumption of GOS-containing milk formula. [33-34] Chiang et al. demonstrated that these patients were sensitized to short chain (sc) GOS and fractions of scGOS containing 3 sugar units or greater but not to cow’s milk or long-chain fructo-oligosaccharides.  These reactions occur more commonly in atopic individuals and the prevalence of GOS allergy is estimated to be around 3.6% in the atopic Singaporean population.  The primary sensitizer for GOS allergy in South East Asia currently remains unknown, but is postulated to be a trigger that is specific to Asia.
Bird’s nest allergy & other food delicacies
Bird’s nest is a Chinese delicacy derived from the edible nest of swiftlets (Collocalia spp.) and is widely consumed in many parts of Asia, in particular Hong Kong, China and Singapore, and is acclaimed for its nutritious and medicinal properties. It was the commonest cause of food-induced anaphylaxis in Singaporean children in the 1990s.  The putative major allergen is a 66-protein protein.  In a more recent cross-sectional study on anaphylaxis admissions in a Singapore tertiary pediatric hospital, bird’s nest was the fifth most common cause of food-induced anaphylaxis after seafood, peanuts, treenuts and egg.  Other food delicacies such as silkworm pupa, bullfrogs, locusts, cicada have also been implicated as triggers of anaphylaxis in China. [38-39]
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About Elizabeth Tham (Editor)
Dr Elizabeth Tham is currently Consultant and Head of the Division of Paediatric Allergy, Immunology & Rheumatology at the Department of Paediatrics, Khoo Teck Puat - National University Children's Medical Institute, National University Hospital, as well as Assistant Professor at the Department of Paediatrics, Yong Loo Lin School of Medicine, National University of Singapore. Her research interests are in atopic dermatitis, food allergy, early life immunomodulation and Developmental Origins of Health and Disease (DoHAD). In particular, her research focuses on elucidating endophenotypes of atopic dermatitis and food allergy and the role of the skin, gut and environmental microbiomes in modulating AD and food allergy risk and disease control in children and their translational relevance for improvement of clinical care.