This month we ask: ''Are food allergies becoming more common, or is diagnosis improving?''
Specialist Scientist (Cellular and Molecular Sections)
Charing Cross Hospital
I think the answer to both questions is “yes”. Food allergies have increased significantly over the last 30 years, with over 150 targets deemed to be possible allergens. The reason for the increase in IgE and non-IgE mediated allergy is unknown, but it is thought improved hygiene standards, changes in diet and changes in the food industry are responsible. In addition, the guidance offered to pregnant and new mothers, recommending avoiding or delaying the introduction of various foods, such as peanuts, has been ill-advised and potentially detrimental in some cases.
For IgE mediated allergy, diagnosis relies on history and is supported by skin prick and blood tests. There has been a great improvement in the range and reliability
of allergy tests. These can help confirm the clinical history and guide the prognosis, especially in children who may grow out of milk/egg allergies. Advances in molecular allergy testing allow assessment of the risk associated with ingestion of (in particular) peanut and tree nuts and in the future may help guide immunotherapy/de-sensitisation therapy. Automation means that many of these tests may now be done in multi-disciplinary laboratories and allergy testing is no longer a niche test.
Allergy tests do have some limitations, as the presence of IgE (sensitisation) to food is far more common than the symptoms caused by food allergy. Indiscriminate testing of food allergen is not recommended and tests work best when interpreted with clinical history.
Lab Manager, Department of Immunology
Barts Health NHS Trust
The overall prevalence of allergy worldwide has certainly increased over the last 30 years, with a trebling in the diagnosis of allergic rhinitis and eczema in children over that time. GP consultations for hayfever during the period have risen more than 250%. Anaphylaxis admissions have increased by 700%, food allergy by 500% and urticaria and angioedema by 100% and 40%, respectively.
The rates reflect a change in overall hospital admission attendance and an upward trend in demand on the health service linked to a growing population and a changing reliance on healthcare.
The UK has an environment that promotes a range of aero-allergen sensitization, for example to house dust mite, tree, grass and mould pollens. The respiratory tract is usually the primary route of sensitisation with cross reactivity then developing to shared determinants in foods.
The rise of a fast food culture make people more likely to be exposed to a wider range of food allergens. Awareness has been heightened with publicity on high-profile food allergy in particular in the popular press.
Testing methodologies have allowed us to make a more accurate and rapid diagnosis of specific IgE sensitisation and explain cross-reactive allergy better. Irrespective of the tests we perform, allergy remains a clinical diagnosis and this appears to be a true epidemic and not simply the result of improved diagnostic pathways and techniques.
Divisional Manager Infection and Immunity
North West London Pathology
There is a good understanding that there is an increase in food allergies and in the number of severe allergic reactions presenting in A&E. However, firm prevalence data is limited. The increase is thought to be multi-faceted with no single explanation. Increased frequencies have been associated with western lifestyles with urban areas showing more prevalence than rural. There are epidemiological variances seen in migration studies, with offspring of immigrants coming from a country with low incidence acquiring the same incidence as the host country.
The theory of dual allergen exposure shows that there is a direct relationship between childhood eczema and peanut allergy. Our diets are changing with global access to foods not previously available, or foods being used more frequently in more easily accessible formats. The hygiene hypothesis is linked to increasing allergies, with a lack of stimuli due to decreases in childhood infections. IgE responses were originally designed to fight parasites, which are an uncommon encounter in western society. Increases in vitamin D deficiencies are linked, as vitamin D is required for a healthy immune system. Diagnosis is still reliant on skin prick testing, however the introduction of component-resolved diagnostics is improving diagnostic accuracy. Further use of novel diagnostics will continue to improve diagnosis.