Allergy Database Service: The FSA Nut Allergy Clinical Database and Serum Bank
Tuesday 5 August 2003
This research project aimed to improve clinical management of food allergy by analysing detailed clinical and laboratory data from patients attending a local allergy clinic with suspected nut allergy.
Allergic disease is one of the major causes of illness in the UK, and with one in three of the population experiencing allergic symptoms at some time in their life, the UK has one of the world’s highest incidence rates. The overall incidence of allergy has tripled in the last 20 years and there is some suggestion, although it is not totally clear, that rates of food allergy may 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 relatively poor predictive value and are of low specificity. In addition the factors affecting the food allergic status of an individual are still poorly understood. Once diagnosis of food allergy is made, the clinician currently has few therapeutic options, relying mainly on a regime of avoidance of the allergen.
The aims of this research project were two-fold:
- To gather into an allergy database retrospective clinical and laboratory information on all nut allergic patients attending Manchester nut allergy clinics. This information was analysed to identify areas where clinical management could be improved, establish the standards for future clinical audit and increase our understanding of factors affecting allergic status to inform policy and advice to consumers.
- Complimentary to the nut allergy database, residual blood taken for routine allergy tests has been 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.
- 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 arising from asthma and rhinitis or compliance in carrying emergency medication;
- It is often perceived by patients with a minor nut allergy that they at high risk of a possible fatal reaction at any time. However, the findings of this study would indicate that the symptoms experienced during subsequent reactions will be similar to those experienced during their first reaction. This supports the practice of offering Epipens to only those that have experienced respiratory or cardiovascular symptoms;
- Peanut allergy has the reputation of being the most dangerous food allergy but it is not clear if this is true. In the UK, 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 dangerous. This was not the case from the results of this study;
- The life threatening symptom of pharyngeal oedema was induced twice as often by tree nuts than by peanut. Brazil induced pharyngeal oedema in 61% of reactions, half of which caused difficulty swallowing or breathing. It also produced 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 anaphylactic shock. Brochospasm was induced equally by peanut and tree nuts. 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 and pistachio, almond and hazel nut, and almond and 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, mono-specificity 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 sensitisations, 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.
Analysis of data from more than 1500 patients referred to the Manchester allergy clinics since the inception of the nut allergy database has produced the following 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.
- On the basis of the findings, the researchers recommended 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. They also recommended increased avoidance.
Click here to view the Final report for project ZT0702
Summers et al. 2007 Factors predicting anaphylaxis to peanuts and tree nuts in patients referred to a specialist center. Journal of Allergy and Clinical Immunology, Sep 120(3):638-646