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What is food allergy? |
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Food allergy is a specific unwanted response to a particular food. For example, most people could drink a glass of milk or eat an egg without problems, However, In a small number of people their body’s immune system responds to that food unfavourably. There are many kinds of reactions to foods. Dr C Motala |
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How common are adverse reactions to food among children, adolescents and adults? |
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Very few prevalence studies have been done. The available studies give an average prevalence of adverse reactions to food of around 12% of the population in all age groups. Adverse reactions to food are of the same magnitude in all age groups, and not a specific problem for infants, which is the common belief today. The prevalence of true food allergy is unknown. |
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How common is food allergy? |
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How common are adverse reactions to food additives (colours, preservatives, antioxidants and flavours)? |
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The contribution of food additives to adverse reactions to food appears to be very small, but the true prevalence is unkown. The evidence shows that food additives provoke or exacerbate existing conditions, but do not induce them. Food additives are defined as пїЅchemical substancesпїЅ. However, there are allergenic substances of biological origin (such as guar gum), which might also be considered as additives. These are able to induce allergic reactions. |
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What foods may cause a food allergy? |
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Nearly any food can cause food allergy. Amongst the most common are cow milk,egg,wheat,peanut and fish. Dr C Motala |
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What kind of allergic reactions do we see? |
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Other reactions can start many hours or even a day or two after eating the food. These include pains in the tummy, vomiting, diarrhoea and eczema, In babies, food allergy can cause colic, but not all colicky babies have food allergy. Rarely, a severe collapse that can threaten the life of a person can be due to food allergy. It is for this reason that any severe reaction to food be taken seriously. Symptoms such as fatique, hyperactiuity, irritability and depression are rarely due to food allergy. Dr C Motala |
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Which symptoms are most common in adverse reactions to food? |
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It is surprising that among the variety of clinical symptoms the majority of food allergic reactions involve the skin. Other common symptoms involves the gastrointestinal tract and the respiratory tract (asthma). |
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Which symptoms are the most severe? |
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Anaphylaxis, which is a life threatening condition. Food anaphylaxis is a syndrome which describes a classic allergic reaction to food or food additives involving immunoglobulin E (IgE) and the release of chemical mediators from the mast cells. It is characterized by the following symptoms: generalized urticaria, angioedema, swelling of lips and throat, shortness in breathing, fall in blood pressure and unconsciousness. Anaphylaxis may be fatal. It has been suggested that more people die of food induced anaphylaxis than of insect stings. Food allergic patients with asthma run a higher risk of developing anaphylaxis than other food allergic patients. |
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How can an anaphylaxis be treated? |
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The first measure is an immediate injection of adrenalin (epinephrine). Patients with a known risk for anaphylaxis, especially those allergic to fish, peanut or nuts should have a prescribed, пїЅready-to-useпїЅ adrenaline device, with them at all times. |
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How common are adverse reactions to food in asthma? |
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The true prevalence is unknown. Figures between 2% to 27% have been proposed in the literature. |
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Does food allergy play a role in atopic dermatitis/atopic eczema? |
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Over 30% of children with atopic dermatitis may have food allergy. In adults the figure is somewhat lower. Recent studies show a very high incidence of food allergy (50-96%) in moderate and severe atopic dermatitis in children. |
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How is food allergy distinguished from food intolerance? |
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Food allergy is an immunological response to food, while food intolerance is a non-immunological response. Food allergy may be identified by an IgE determination, but there are also other immunological mechanisms not easily differentiated. Lactose intolerance is a non-immunological disease which is due to an enzyme deficiency. Coeliac disease involves the immune system, but the mechanism is not fully understood. |
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Which food allergens are most common? |
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In children: Egg, cowпїЅs milk, soy bean, peanut, wheat, and nuts. In adults: Shellfish, fish, nuts and peanut. Patterns of the most common allergens vary geographically and culturally. |
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Do all children outgrown their food allergy? |
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Studies have demonstrated the disappearence of food allergy symptoms in up to 1/3 of children and adults in one to three years, though positive skin tests and positive serum IgE levels may persist. Evidence suggests that the probability of outgrowing a food allergy is dependent upon the food allergen and the patient’пїЅ compliance with the elimination diet. Allergies to peanut, nuts, fish and other seafood appear to be more persistent. |
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How large is the risk of child developing allergy, if there is a positive history of atopy in the family? |
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If one parent has atopic disease, the risk of developing allergies in the offspring is about 37%. If both parents are affected, the risk increases to about 62%. |
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How should food allergy be treated? |
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A total elimination of the identified food from the diet is the recommended treatment in severe cases of food allergy. A correct diagnosis is very important, especially when a patient risks undernourishment. When nutritionally important foods are eliminated, a re-evaluation of the patientпїЅs sensitivity should be done by repeating challenges and IgE determinations at appropriate intervals. This is especially important for small children. In cases of multiple food allergies, a specialist should be involved because of the risk of undernourishment. |
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Can food allergy be treated with immunotherapy? |
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Immunotherapy for food allergy is currently not in use in routine clinical practice. |
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Is there cross-reactivity between foods? Do food and pollen cross-react? |
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Yes. Typical examples of cross-reactivity between foods are wheat rye, cod haddock, peach apricot. Food and pollen cross-reactivities are apple birch, celery mugwort, hazelnut birch pollen and cereals timothy pollen. While these and other cross-reactivities exist, few patients are aware of them. Suspected cases of cross-reactivity must always be tested and clinically confirmed. |
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How can food allergy be diagnosed? |
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A true allergic reaction will occur each time the problem food or foods are eaten. Thus the parents careful description of what happens with different foods can be helpful. Skin tests and blood tests to measure the body’s degree of sensitivity can be helpful for foods such as cow milk, egg, peanut, nuts and fish. A very large skin test reaction can be diagnostic, These tests can identify nearly half the children with allergy to cow milk, egg, peanut and fish, However not every child with atlergic reactions will have positive skin or blood tests. The most important test is a challange with the problem food. In this test, foods suspected of causing an allergic reaction are carefully given to the child under the watchful eye of specially trained staff. Some children also require special tests of bowel function to assist in diagnosis. |
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What is a double-blind placebo controlled food challenge (DBPCFC)? |
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A double-blind food challenge (DBFC) is a test where neither the patient nor the physician know which food is administered. The placebo controlled version (DBPCFC) is considered to be the пїЅgold standardпїЅ for diagnosis of adverse reactions to food. Despite this there are certain drawbacks with DBPCFC. There are no standardizations of dosage and time intervals between challenges. DBFC is difficult to perform in the routine clinical setting because it is time-consuming and expensive (approx $1000 per patient). Do skin tests and IgE determinations give different results? Skin tests and blood tests are both used in the diagnosis of IgE-mediated reactions to allergens. A positive skin test is dependent not only on IgE antibody but also on mast cell integrity and vascular and neural responsiveness. Under ideal conditions, prick/puncture skin testing provides con-cordant results with optimized in vitro IgE antibody tests. However, skin tests are not quantitative, and the results cannot be compared between clinics. In contrast to in vitro tests, skin tests are dependent on the skin status, and are influenced by medication and the way the test is performed. There is a small, however finite, risk of systemic reactions induced by skin tests. Compared to food challenge (DBCFC), the original technology Phadebas RAST was shown to be more sensitive than skin test in adults. In vitro testing with Pharmacia CAP System RAST testing. |
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Why perform specific IgE tests, when food reactions are often immediate, and easily detectable by the patient? |
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About half of all IgE mediated reactions to food occur more than one hour after ingestion. Symptoms like skin reactions and/or asthma are most common for these non-immediate reactions. In these cases the patient is rarely certain about the reason for the reaction. Immediate reactions are typically mouth irritation, swelling or vomiting. In these cases the patient is usually aware of the foods responsible. This must in any event be confirmed. If the reaction has been severe such as an anaphylaxis, it is important to complete an IgE determination to correctly identify the allergen. In such cases a food challenge or skin test could be dangerous. The search for the causative allergen may be laborious because the patient is usually unaware of what was eaten and when. пїЅHidden allergensпїЅ, causative allergens of which the patient is unaware, can pose problems. The difficulties associated with reading and interpreting food labels is also a problem in this context. |
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Why perform in vitro IgE determinations, when skin tests are said to give the same results? |
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Because IgE tests performed with in vitro tests:
Unlike skin test results, in vitro IgE results from Pharmacia CAP System are quantitatively comparable between laboratories and over time. |
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Is the maternal diet of importance during pregnancy and lactation to prevent the development of atopic diseases? |
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At the moment, this is a much debated issue, and there are several different opinions i |