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Allergy Database Service:The FSA Nut Allergy Clinical Database and Serum Bank

Project Code: ZT0702

31/10/2006

Immunology Department, Manchester Royal Infirmary
Summers, C

Background

Recently described by the Royal College of Physicians as the "Allergy Epidemic”, allergic disease is one of the major causes of illness in the UK. With one in three of the population experiencing allergic symptoms at some time in their life, the UK tops the worlds’ incidence rates. The incidence of allergy has tripled in the last 20 years and there is some evidence that rates of food allergy have risen alongside the documented increase in respiratory allergy. Hospital admissions for anaphylaxis have increased seven fold over the last decade.

Despite this the diagnostic tools available to the clinician have poor predictive value and are of low specificity. The factors affecting the food allergic status of an individual are still poorly understood. Once diagnosis of food allergy is made the clinician has little therapeutic options relying mainly on a regime of avoidance of the allergen. Such an approach unfortunately reduces the quality of life of the patient and their family.

Objectives of the study

1. To gather retrospective clinical and laboratory information on all nut allergic patients attending our allergy clinics. This information will be analysed to identify areas where clinical management can be improved, establish the standards for future clinical audit and increase our understanding of factors affecting allergic status.

2. Complimentary to the Allergy database, residual blood taken for routine allergy tests has been (and continues to be) banked. This has been used to address areas of research highlighted by the allergy database, by us as part of this project or in collaboration with others as part of other projects.

The results are presented and summarised in the form of four papers (see pages 11 to 76), which will be submitted for journal publication.

Main Findings

A patient’s avoidance in different circumstances was often inconsistent; some exercised extreme avoidance with no evidence of nut allergy. Extreme avoidance adversely affected the perceived quality of life. Many repeat, severe and fatal reactions to hidden allergens occurred because patients were not aware of the ingredients of catered food. Festive food and foreign travel were common sources of reactions. Other sources of reactions to nuts included, social pressure or alcohol which caused less careful avoidance than intended by the strategy; labels could not be read or were misinterpreted; requests for allergen-free food were not complied with and for some, no reason was found for avoidance failure.

We recommend a systematic review of patients’ avoidance behaviours: accurate identification on labels of allergens and written information about high risk foods and circumstances will improve patient safety. We recommend increased avoidance. Young adults with severe asthma and/or rhinitis who ingest peanut containing food are at greatest risk in having a severe life threatening reaction to peanut. Differences observed with age may be related to maturity of the immune system, airway remodelling in response to insults due from asthma and rhinitis or compliance in carrying emergency medication.

It is often perceived by patients with a minor nut allergy that they are a walking time bomb with a possible fatal reaction just round the bend. This report would rather indicate that the symptoms experienced during their first reaction will be similar to subsequent reactions. This supports the practice of offering Epipens to only those that have experienced respiratory or cardiovascular symptoms.

Peanut allergy has the reputation of being a killer but is it truly the most dangerous? Peanut allergy is much more prevalent than any of the tree nut allergies so the number of fatal reactions should be greater if peanut and tree nuts are equally deadly. This was not the case from our results.

The life threatening symptom of pharyngeal oedema is induced twice as often by tree nuts than by peanut. Brazil induces pharyngeal oedema in 61% of reactions half of which cause difficulty swallowing or breathing. It also produces more severe angiodema which in extreme cases can obstruct air ways. Walnut and cashew also show twice the incidence of hypotension that can kill through shock. Brochospasm is induced equally by peanut and tree nut. Individuals with tree nut allergy are more likely to experience a life threatening reaction than those with peanut allergy alone.

There are distinct patterns of sensitisation with single tree nut sensitisation being rare. A strong relation exists between Cashew / Pistachio, Almond/ Hazel and Almond/Peanut. Sensitisation to a broad spectrum of nuts is common even in very young children. It is likely that this is due to a combination of sequential exposure and cross reactive epitopes/allergens. The very young tend to be mono specific (i.e. sensitised to one nut species only). This changes gradually to predominantly poly specific in the late teens as they are exposed to different nut types. As the population age approaches late adulthood monospecificity again predominates. This may be due to loss of sensitivity or a different mechanism of sensitisation in adults that resists poly-sensitivity. Over time a quarter of the population lost sensitisation to at least one nut which supports previous reports that nut allergy can resolve. Considering the predominance of multiple nut sensitisation few gain new sensitivities. A combination of inherent cross reactivity and sequential exposure to different nut types is responsible for the poly sensitisation observed particularly in late teenagers.

The serum bank has proven a valuable resource resulting in a number of trans -European collaborations being set up. It has also attracted funding to carry out a number of fundamental research projects on the food allergic process.

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