Development of symptoms within two hours of ingestion of the suspected food may be reasonably classified as an acute reaction. These reactions are commonly due to milk, egg, fish and nuts (Table 5.6). The person may or may not know the food responsible. In children, allergic reaction may occur to the first known exposure to a food such as cow's milk, egg or peanut. It may also develop in an
Table 5.6 Foods commonly implicated in the anaphylactic reactions
Tree nuts: brazil nut, hazelnut, almond, walnut, pistachio, cashew nut, pecan Cow's milk Soya milk Fish/shellfish
Egg adult to a food previously well tolerated although this is uncommon. Acute allergic reactions are usually IgE mediated.
Allergic reactions occur as a result of interaction of allergen with IgE antibodies bound to receptors on the surface of mast cells. This interaction results in the release of mediators such as histamine, heparin, bradykinin, prostaglandin and leukotrienes. The allergen may come from a variety of sources such as foods (e.g. peanut), drugs (e.g. penicillin), insects (e.g. bee venom), etc. The reaction may involve one or more systems and may be mild, moderate or severe.
Assessment of severity (mild, moderate and severe)
The severity of reaction depends on sensitivity of the patients to food allergen and the amount ingested. Patients with life-threatening symptoms such as respiratory difficulty due to laryngeal oedema or severe bronchospasm and/or hypotension should be regarded as having a severe reaction or anaphylaxis.13 Troublesome, but not immediately life-threatening, reactions such as generalised urticaria/angioedema and bronchospasm of moderate severity may be termed severe allergic reactions. Sometimes the reaction is mild and confined to an organ or system, for instance oral or gastrointestinal symptoms or localised urticaria.
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