It has been estimated that approximately 1-2% of adults but 6-8% of children suffer from a food allergy. However, only 2-5% of children under the age of 6 have had there food allergy confirmed.
It is important to correctly define what type of food reaction occurred after ingestion of an offending food. Simply, an adverse food reaction can either be secondary to a food allergy or a food intolerance. A food allergy is the result of an exaggerated response of the immune system to the food (hypersensitivity). A food intolerance does not involve the immune system. A classic example of a food intolerance is lactose intolerance which is a problem of lactose absorption due to an enzyme deficiency (lactase). The symptoms of bloating, cramps, flatulence, and diarrhea are also present in a true milk protein allergy which sometimes leads to the misdiagnosis of a milk allergy. Other food intolerances can be due to toxic reactions and psychologic aversions.
After eating the food the allergic individual will start suffering symptoms within a couple of minutes to a few hours. Mild symptoms can be a runny nose and sneezing. More severe symptoms include swelling of the lips, tongue, and throat (angioedema). Other food allergic individuals may suffer only gastrointestinal symptoms, hives, eczema, cough, or wheezing. The most severe allergic reaction is called ANAPHYLAXIS and is a medical emergency.
The major food allergens for children include milk, eggs, peanuts, soybeans, wheat, fish, and tree nuts. In adults the major food allergens are peanuts, tree nuts, fish, and shellfish. The foods that are more likely to lead to anaphylaxis are peanuts, tree nuts, and shellfish. Individuals allergic to one food may also be sensitive to related foods (cross-reactivity). For example a peanut allergic person may also react to soy, peas, and certain beans. In children after 1-2 years of strict avoidance of the offending food, 1/3 will lose their sensitivity. Generally this holds true for eggs, cow's milk, and soy allergy. Sensitivity to peanut, tree nuts, and shellfish are considered to be life-long.
The diagnosis of a food allergy is done by first taking a detailed medical and diet history. Further testing of suspected foods is then completed by either skin testing or blood testing (RAST). A negative skin test rules out an allergy with an accuracy of greater than 95%. A positive skin test has only a 50% accuracy of correctly diagnosing an allergy. RAST is less sensitive than skin testing but still very useful in ruling out food allergies. A positive skin test or blood test usually should be confirmed by an oral food challenge.
This brings us back to our student. She was given ? a teaspoonful of peanut butter to eat. About 3 minutes after ingestion she stated that her ears and throat were slightly itchy. No other physical signs were noted. A couple minutes later the itching had gone but now she complained of a sore stomach. About two hours after she ate the peanut butter she started to vomit. Her face became red and she started to cough and have difficulty breathing.
She was immediately given an injection of epinephrine and an asthma breathing treatment. Within minutes the entire allergic reaction had reversed. She felt fine and actually wanted to go back to school!
A couple of excellent points about food allergy can be learned here:
- Mild symptoms must be taken seriously. As more of the food is digested and the protein absorbed in the intestines the reaction will get worse. If, for example, Benadryl was immediately administered when she felt itchy, the severe anaphylactic reaction could have been averted. In this case the reaction was allowed to continue because this was a confirmatory challenge obviously done in a controlled setting. Oral challenges generally should be done in a doctor's office if there is any chance that a severe allergic reaction might occur.
- Epinephrine is life saving if administered quickly. Most deaths from food allergy occur either because the epinephrine injector was left at home or was not given in a timely manner after symptoms started. The most common epinephrine injector available is the Epipen which comes in two strengths. The Epipen Jr (0.15mg) is for children who weigh 10-20kg and the Epipen (0.3mg) is for children greater than 20kg. It is important that the correct strength is left in the health room. Epipen usually need to be replaced on a yearly basis due to the expiration date.
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