Nut Allergies

Recognizing and Dealing With Nut Allergies

Recognizing and Dealing With Nut Allergies


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The accuracy of diagnostic tests

Every disease has a rate of prevalence and incidence within both the general population and specific populations. The term 'prevalence' is a statistic based upon a particular point in time. It refers to the number of cases of a particular disease divided by the total number of people within the population and is usually represented as a percentage. 'Lifetime prevalence' is the number of people within a population who may have a particular disease at some time in their life, expressed as a percentage of the total population. The term 'incidence' refers to the number of new cases of a disease occurring over a specified period of time. The two terms are useful for different kinds of disease. The prevalence of a disease is often useful for more chronic diseases - those diseases which people rarely recover from, but also rarely cause death. A useful example is an estimate of the lifetime prevalence of peanut allergy within a given population. Diseases with high recovery rates or with high...

Foods commonly associated with allergy Table

These foods are associated with the development of antibodies (sensitisation) that typify the immediate allergic response - IgE antibodies. After sensitisation very low doses can cause immediate allergic reactions.9 For instance, 76 of subjects with peanut allergy experience symptoms within five minutes and 93 within 30 minutes, and 90 reported symptoms after eating less than one peanut.10

Clinical categorisation of allergic reactions

In a series of 62 adults and children with peanut allergy, Ewan18 divided patients into those whose separate symptoms were Sicherer et al.20 showed that in 102 individuals with peanut allergy, the first reaction is characterised by isolated skin reaction in 49 , by respiratory reaction only in 2 , by both skin and respiratory in 17 , by both skin and gastrointestinal in 7 , and by all three systems in 21 . None of this group of peanut-allergic individuals suffered a significant fall in blood pressure or loss of consciousness on first exposure.20

Comparison of allergen contents of different foods or food sources

ELISA with a standard curve provides information on quantities of specific allergens. Sometimes it is necessary to compare one extract with another to determine if the allergens present are the same (homologous) or different (heterologous). This is useful for determining if a particular treatment reduces or increases the allergenicity of a particular food source, for example whether hydrolysis has removed cow's milk allergens from infant formula. It is particularly useful for determining if a food causing an allergic reaction was contaminated or contains cross-reacting proteins with another known allergen, e.g. a food containing hazelnuts that caused a reaction in an individual with peanut allergy. Figure 7.3 shows a schematic representation of an ELISA inhibition to determine the similarity of two allergenic food sources. This assay may also be adapted to provide quantitative data where the percentage inhibition obtained with dilutions of a homologous antigen to the one bound to the...

Additional communication initiatives

Key allergens which make food selection much quicker and easier. The lists are available from the companies directly and are often on the Internet. Once again peanut and nut allergies are often handled as a special case, as they are the most common food causes of anaphylaxis. 'Free-from' lists are updated every six months to reflect any changes that may have occurred. Users of lists are also advised to check ingredients' lists, particularly where a 'new recipe' or 'new improved' flash indicates a recipe change. In the case of anaphylactic reactions information must always be accurate and up to date. Peanut and nut-free lists are often controlled closely and carry a 'Use by' date after which that list is invalid and recipients are asked to contact the company for an update. During the 'shelf life' of the list it is recommended that the names and addresses of all recipients are held. Should any changes occur to that list whilst it is 'live', all recipients can be contacted to advise...

Support organisations for individuals with food intolerance

In October 1993, my 17-year-old daughter Sarah died of an overwhelming allergic reaction after going into a restaurant and eating a slice of lemon meringue pie containing crushed peanuts. Sarah had thought she was only mildly allergic to peanuts and had no idea that an allergic reaction could kill. National newspaper and television reports referred to 'a very rare allergy to peanuts'. But its rarity was challenged by letters which subsequently appeared in a few of the newspapers letters written by the parents of children with nut allergy. What was significant was that these parents had received little medical guidance about their children's allergy they were coping alone. It also became clear there was a similar lack of knowledge and information within the food industry, and manufacturers and retailers had little or no idea that a major issue was about to break.

The Anaphylaxis Campaign

The Anaphylaxis Campaign, of which I am director, was set up early in 1994 following five well-publicised deaths caused by allergic reactions to peanuts or tree nuts. Those who died included my teenage daughter Sarah, whose death was particularly shocking because her previous allergic reactions to nuts had been mild. As a journalist, I had some expertise in gathering information and there were indications early on that, far from being rare, nut allergy was really quite common. Supported by my MP, Cranley Onslow, I set in motion the beginnings of an awareness campaign. However, I was not alone. Following the intense national publicity, several parents of children with nut allergy came forward and we formed the core group of the Anaphylaxis Campaign. As knowledge of the group spread, we found we were overwhelmed with letters from families similarly affected 60-70 per day in the first few weeks. By early 2000, membership stood at around 5500. Members pay 5 a year.

Collaboration with governments

Article stated that Sue Nichol, the mother of a son with peanut allergy, was urgently trying to form a lobbying group of parents to get together to fight for improved food labelling. By February 1994, the Anaphylaxis Campaign already had several hundred members or potential members, each one with a story to tell. Assuming the cases were all genuine - and most of them were - it was clear that the Anaphylaxis Campaign had a large storehouse of information. This file was given added credibility by Dr Rita Brown, consultant allergist at the Royal Berkshire Hospital, Reading, who provided the Anaphylaxis Campaign with evidence gleaned from her own work with nut allergy patients. A written report I compiled for MAFF reported her view that anaphylactic reactions are much more common than has been recorded and it is likely that some deaths from anaphylactic shock go undetected. She said that out of 663 consecutive new patients referred to her for allergy assessment, a total of 34 had suffered...

Collaboration with the food industry retail and manufacturing

In response to the exasperation expressed by members, the Anaphylaxis Campaign has raised the issue on many occasions during discussions with retail companies. We believe there may be some room for manoeuvre. Supermarkets are probably right to discourage people with nut allergies from eating cakes or pastries bought in their in-store bakeries, but they might reduce risk where bread-making is concerned. Managers might look at their operations and consider whether it is possible to dedicate their bread-making area as a nut-free zone. Instead, most of them effectively put in-store bakery products out of bounds for people with severe allergies. I will be returning later to the general problems of cross-contamination and disclaimer labelling.

The use of disclaimers on food labels

A key question is How likely is it that someone with nut allergy will come across a particle of nut on, say, a spoonful of breakfast cereal that is supposed to be nut-free The answer is that it is probably very unlikely indeed, but it does occasionally happen. A young boy visiting a football match with his grandfather decided at half time to have his usual treat - a milk chocolate bar that he had eaten many times before. He suffered a mild allergic reaction. Looking at the label he saw the warning in small print 'May on rare occasions contain nut traces.' This kind of incident may be rare, but the risks have rung alarm bells in the food industry.

The catering industry

A far more tragic case involved a 13-year-old Aylesbury girl who was allergic to peanuts. A family friend offered to go to the local Chinese and collect a takeaway and the youngster ordered a portion of chips with curry sauce. When the friend returned, the girl took one bite of the chips coated in sauce and decided she didn't like it. It transpired that the chef had used peanut butter to make the sauce. The girl died of anaphylactic shock. The restaurant staff had never heard of peanut allergy and did not state on the menu that sauces were made with peanut butter. Returning to the cold reality, we have the case of a young woman with nut allergy who died after going out for a meal with colleagues in a top hotel in 1995. She was unaware that the butter contained nuts. We have the case of the 18-year-old economics student who died when she suffered an overwhelming allergic reaction to nuts in a dessert during her first night at Cambridge University in 1998. We have the 19-year-old man...

Research into allergy and intolerance

Other questions occupy the forefront of our thinking. Why is nut allergy particularly dangerous Are there other foods that may be climbing up the allergy table Today peanuts - what next Might there be a way to identify 'high-risk' allergy patients early in life If this were possible, it would release an intolerable burden from those who think they are at risk of a severe reaction, but may not be. Should everyone with peanut allergy be offered adrenaline Or are those who advocate adrenaline for all nut allergy patients generating needless complications

Implications of study design

An example of a case-control study, is one looking at the aetiology of peanut allergy. It was concluded that children sensitised to peanut had a higher level of peanut exposure in utero due to higher maternal consumption (Frank et al. 1999). This result, which has not been confirmed in cohort studies, probably occurred because of recall bias as the mothers of infants with peanut allergy, are likely to have spent more time considering their consumption of peanuts during pregnancy prior to filling in the study questionnaire. Despite these potential problems, case-control studies represent a rapid way of providing important evidence about a hypothesis that can be later tested using a more definitive approach.

Interpreting data on the natural history of food allergy

Cohort studies have been very successful in delineating the natural history of allergies to foods such as cows' milk and egg because they are almost completely outgrown within a few years. For longer lived allergies, such as fish, shellfish, peanut and tree nuts, the natural history is less clear because of the difficulties in interpreting the available data. This is illustrated by results from an interview survey investigating the prevalence of peanut allergy (Emmett et al. 1999). The data (Figure 10.3) suggest that more males are affected in childhood whereas in adulthood peanut allergy is more prevalent in females. There are a number of possible explanations for these results. Firstly, peanut allergy may be outgrown at an earlier age in males. Secondly, peanut allergy may be acquired later in females. Thirdly, there may be a combination of both of the above. Fourthly, the data may be explained by a cohort effect the adult generation surveyed may have a lower inherent risk of...

Common food allergies

Table 10.10 compares clinical reactions to foods, and Table 10.11 compares skinprick specific IgE reactions to foods, between allergy clinic populations from different countries. As such they deal with a selected population and some studies involve small numbers. They show that cows' milk and egg are among the 2-3 commonest foods causing allergy in most countries. Peanut, fish, soy, wheat and shellfish are among the next most common groups of foods causing allergy, although significant variations occur between countries. Thus, for example, shellfish allergy appears to be more common in countries such as the Philippines, Thailand and Singapore where it is a part of the staple diet from early infancy, than in many other countries where it is consumed later and less commonly. In contrast, clinical peanut allergy which is a big problem in Western countries appears to be less common in most Asian countries, and also in Spain (Crespo et al. 1995). Thus in Japan it is very rare (Hill et al....

Crossreactions between foods

Cross-reactivity is due to a reaction to identical or similar protein allergens that occur in more than one food, or in a food and an inhalant pollen. This is different from associated reactivity where two or more food allergens may be seen to be associated epidemiologically. A good example of the latter is the high rate of association between egg and peanut allergy although the allergens are not related. Establishing a cross-reaction requires the demonstration of at least a positive correlation between the magnitude of specific IgE to both foods, and RAST inhibition studies are needed for confirmation. Cross-reactivity is seen at an immunological level when a subject is sensitised to both foods on the basis of positive skinprick or specific IgE testing to both foods. However, often only a smaller proportion will demonstrate clinical cross-reactivity, that is a reaction to both foods on clinical exposure.

Maternal intervention

Retrospective and uncontrolled, but suggested that in an atopic population the consumption of peanuts by mothers during pregnancy and lactation was associated with an earlier onset of peanut allergy in the children. There was no difference in the cumulative incidence of peanut allergy, and timing of immunological sensitisation to peanut was not assessed. An alternative explanation of the data is that the children of mothers consuming peanuts during pregnancy and lactation had the opportunity to consume peanuts earlier in life than those whose mothers did not eat peanuts. Furthermore, the findings of this study are not supported by a study based on the Isle of Wight birth cohort (Tariq et al. 1996). This study showed no effect of reduced no maternal nut ingestion in pregnancy on the development of immunological or clinical reaction to nuts in a non-randomised population followed up until four years of age.

Peanuts and tree nuts

Over the last few decades, peanuts have become a ubiquitous part of the Western diet as they are a versatile form of easily digested protein (Lucas 1979). In a study looking at the use of dietary manipulation to prevent the development of food allergy, all infants in the control group were exposed to whole peanuts by their second birthday (Zeiger et al. 1989) occult exposure probably occurs even earlier. Adverse reactions to peanuts and tree nuts are generally IgE mediated, occurring rapidly with subjects presenting with dermatological, respiratory and gastrointestinal manifestations (Hourihane et al. 1997). Peanuts and tree nuts are responsible for a third of all admissions with anaphylaxis (Bock 1992). Peanuts are part of the legume family, they are more closely related to peas, beans, soy and lentils than the tree nuts. It has been suggested that there is extensive cross-reactivity between peanut and tree nuts in terms of sensitisation but not clinical reactivity (Sampson and...


Subcutaneous or intramuscular adrenaline is used as the first-line treatment for anaphylactic reaction to food and other allergens.11 The intramuscular route is preferable if there is evidence of circulatory collapse, as the absorption is better than from the subcutaneous site. Patients who are at risk of anaphylactic reactions, for example those with nut allergies, should be provided with a self-injectable adrenaline device. This delivers a set dose of adrenaline by intramuscular route. The adult dose is 300 ig and the paediatric dose is 150 g repeatable after 15 minutes. Patients and their carers should be given instructions in the use of the device in case of emergency. When absorption from the intramuscular route is not adequate, for example in severe hypotension and shock, slow intravenous injection may be used by trained personnel. Inhaled adrenaline is not useful for the treatment of anaphylaxis. However, it may be effective for angioedema or laryngeal oedema in the absence of...


Lower quality waste is not added back to products but disposed of in an appropriate manner. Controls must be in place to ensure there is no cross-contamination of allergens when using rework. The simplest rule when handling rework is to put 'like into like' to prevent any risks. Additionally, rework must be clearly labelled for further internal use within the factory and controls must be in place to ensure it is used correctly. Rework is particularly an issue with regard to nut allergy as trace amounts of an allergen can easily be transferred.

Associated morbidity

Markers of atopy as a whole are associated with an increased risk of developing adverse food reactions. Thus asthma, eczema and rhinitis are increased in children with food allergy compared to the general population (Zeiger and Heller 1995, Hide et al. 1996). The strongest association is between eczema and food allergy, and the risk appears to be greatest in infancy and in those with moderate to severe eczema (Burks et al. 1998, Sampson 1996). The literature appears to be best for peanut allergy. One study found that in peanut-allergic children atopy in some other form was present in up to 96 of subjects (Ewan 1996). In the Isle of Wight birth cohort study half of the children with peanut allergy had asthma and two-thirds had eczema, considerably higher than the rates in the cohort as a whole (Tariq et al. 1996).

Genetic factors

A family history of food allergy in a first-degree relative increases the risk of food allergy approximately fourfold in other family members (Dean 1997). In families with at least two food allergic individuals, the same food is frequently implicated. The best-studied food is peanut whereby if one sibling has peanut allergy then the risk of another sibling having peanut allergy is 7 . This represents a tenfold increased risk compared with the general population in whom the risk is 0.6 (Tariq et al. 1996). However, there is a lack of good literature looking at the risk for other foods and in general there are no studies, such as twin studies, that separate the role of genetic and environmental factors in the development of food allergy. A number of different HLA genotypes have been shown to be associated with different types of food allergy. The data are best for peanut allergy and coeliac disease (Howell et al. 1998, Howdle and Blair 1992).


Data on the relative importance of adverse food reactions in different populations can be derived from case series that rank the relative importance of different food allergies seen in specialist allergy clinics. Important observations emerge from such comparative data. Firstly, egg and milk allergies are the most common food allergies world-wide. Secondly, certain food allergies that are common in Western countries, such as peanut allergy, may be uncommon in Asian countries such as Japan. Thirdly, certain food allergies that are never seen or are extremely rare in Western countries are important causes of allergy in other countries. This forces us to rethink our concept of 'common' and 'uncommon' allergenic foods. Different food allergens are clinically important in different countries mustard allergy in France sunflower seed allergy in Israel lentil allergy in Spain royal jelly allergy in Hong Kong and bird's nest allergy in Singapore. Fourthly, it emerges that foods described as...