Among all persons with food allergies, those who are allergic to peanuts are at greatest risk for anaphylactic symptoms.1 About 30,000 cases of food allergy–related anaphylaxis are seen in the nation’s emergency departments (EDs) each year, and the food most commonly responsible is peanuts.2 What can primary care providers do to reduce the number of peanut allergy–associated anaphylactic reactions and fatalities, both in the ED and in the larger community?
According to a guideline from the National Institute of Allergy and Infectious Diseases (NIAID),3 prevalence of peanut allergy is about 0.6% of the US population, although in an 11-year survey involving more than 13,000 respondents, Sicherer et al4 reported allergy to peanuts, tree nuts, or both in 1.4%, possibly translating to some three million Americans; British researchers have reported peanut allergy in 1.8% of an 1,100-member children’s cohort.5 The risk of exposure to peanuts and the associated risk for severe and possibly fatal anaphylaxis present a lifelong struggle for both patient and family.
ETIOLOGY OF PEANUT ALLERGIES
Food allergy prevalence has reportedly doubled in recent decades, with a significant increase also seen in allergy severity.6 Allergies involving eggs, nuts, fish, milk, and other foods represent the leading cause of hospital-treated anaphylaxis throughout the world.1 Unlike other allergenic foods that affect only one age-group, peanuts are among the foods that trigger the “vast majority” of allergic reactions in young children, teenagers, and adults alike.3
Increases in reported episodes of peanut allergy reactions may be occurring for several reasons:
• Many people have adopted vegetarian diets, and nuts are considered a good protein source6
• Environmental exposures are increasingly common
• More people are genetically vulnerable, as the role of family history becomes clearer
• Food preparation methods (eg, shared processing equipment, contaminated raw materials, formulation errors) and inaccurate labeling lead to accidental exposures7,8
• Exposure to nuts in utero or during breastfeeding is more common.9 Nowak-Wegrzyn and Sampson6 point to the promotion of peanut butter as an economical, nutritious food source for children and for women during pregnancy and lactation; mothers’ consumption of peanuts more than once a week during pregnancy and lactation have been linked to overexposure for their children.9
Other trends that may contribute to peanut allergy prevalence are the early introduction of solid foods in the infant diet and the use of skin products that contain peanut oil.6
Environment and Genetics
The body of knowledge regarding the specific causes of peanut allergy is increasing constantly. Several known peanut proteins (Ara h1, Ara h2, Ara h3, Ara h6, Ara h7, and Ara h9; Ara h8 is a homologous allergen that may account for peanut/birch cross-reactivity) are thought to be responsible for the initial sensitization to peanuts in vulnerable persons, triggering the associated immunoglobulin E (IgE)–mediated response.10-12 Approximately 75% of known peanut-allergic patients will react to these proteins on their first ingestion after being sensitized.9
Since IgE antibodies do not cross the placenta, it is believed that sensitization to peanut proteins must occur in utero or through breast milk. This form of sensitization predisposes these patients to the initial life-threatening anaphylactic reaction.9
There is strong evidence that genetic factors may play a role in peanut allergies.2 In a study of 58 pairs of twins by Sicherer et al,13 heritability of peanut allergy was estimated at 82%, with 64% of monozygotic pairs, versus 7% of dizygotic pairs, showing concordance for peanut allergy. However, the genetic loci that may be responsible for specific food allergies have not yet been identified.2
It is believed that manifestations of food allergy are very similar to those of asthma and atopic dermatitis. According to Green and colleagues,14 82% of peanut-allergic children who visited a referral clinic also had atopic dermatitis. These conditions appear to be triggered by similar mechanisms, mediated by both environmental and genetic factors.2,14-16 Hong et al2 are optimistic about the advances being made in food allergy genetics. Increased understanding, they feel, may lead to new treatment options for potentially fatal food allergies.2
PATIENT PRESENTATION AND HISTORY
As with any IgE-mediated immune response, the patient must have been exposed to the allergen in question. Most patients present with a history of having ingested raw or boiled peanuts and/or foods produced in a facility that also processes nuts.1,18 Clinical symptoms of peanut allergy may develop within seconds of ingestion. For some patients, consumption of as little as 5 to 50 mg of peanut protein can trigger symptoms.19 (A single peanut from a jar of commercially processed peanuts contains approximately 300 mg of potentially allergenic protein.1)
Typically, the most dramatically affected patients have a medical history of asthma or other IgE-mediated immune reactions.1 In one study, young adults with IgE-mediated peanut allergy were found at especially high risk for severe anaphylaxis.6 Seventy-five percent of patients who have a reaction to peanuts do so following their first ingestion (after the initial exposure).
The mean patient age for a diagnosis of peanut allergy is about 14 months; only 20% of the patients diagnosed with a peanut allergy (most likely those with a baseline peanut-specific serum IgE level < 5 kU/L18) will outgrow it by the time they reach school age.18,20 Those who do should be encouraged to consume peanuts on a regular basis; according to Byrne et al,21 8% of patients with allergy resolution experience recurrence, a possible result of infrequent peanut consumption.
Patients with peanut allergies can present with a range of symptoms, possibly involving cutaneous, cardiovascular, gastrointestinal, and/or respiratory systems (see Table 115,22). The more notable symptoms, possibly developing within 15 minutes of exposure, are progressive upper and lower respiratory difficulties, vomiting, diarrhea, hypotension, edema of the face and hands, arrhythmia, throat tightness (in serious cases, approaching anaphylaxis), and possibly loss of consciousness. Such severe reactions often occur in the child who has ingested raw peanuts or tree nuts.22
Milder physical exam findings include erythema, pruritus, conjunctivitis, abdominal pain, nasal congestion, itchy throat, and sneezing. These reactions may have been triggered by foods produced in a facility that also processes nuts, household utensils used to prepare foods that contain nuts, or cross-contamination from another child.9,15,24
The diagnosis of a patient with a peanut allergy is made through thorough history taking, careful physical examination, allergy testing with either a skin prick test (SPT) or serum-specific IgE, and oral food challenges. The gold standard for diagnosing food allergy is the double-blind, placebo-controlled oral food challenge,2,25-27 as this test alone can determine the amount of peanut protein needed to trigger a reaction in the given patient.9 However, this is a difficult test to administer and must be performed under strict medical supervision.21
It has been determined that a wheal size of 8.0 mm or greater on the SPT has a 95% to 100% positive predictive value for peanut allergy.1,26,27 Although conflicting results have been reported in some patients between SPT and the oral food challenge, a negative SPT result is considered useful for excluding IgE-mediated allergic responses.22
Researchers examining the peanut-specific serum IgE have demonstrated a 95% to 99% positive predictive value when serum levels exceed 15 kU/L.26,27 This cutoff value in peanut allergy patients is considered suggestive of allergic reactivity, although negative results on an oral food challenge have been reported in more than 25% of children with serum levels exceeding the cutoff.25-27 Testing may have been to whole peanut extract rather than the molecular components (eg, Ara h8).11,12
This past summer, the FDA approved a component test that detects allergen components that include Ara h1, h2, h3, h8, and h9.11,12 Another specific version of the serum IgE test has been in development, one that measures the patient’s IgE reactions to the Ara h2 and Ara h8 components in peanut protein. Johnson and colleagues10,28 have found an increasing level of serum IgE anti–Ara h2 in children who were unable to pass the oral peanut challenge, whereas serum IgE anti–Ara h8 was higher in those who did pass the challenge.28
The manifestation of anaphylaxis in patients allergic to peanuts or tree nuts can be life-threatening.29 Symptoms include intense pruritus with flushing of the skin, urticaria, and angioedema, upper-respiratory obstruction resulting from laryngeal edema, and hypotension.30 The clinical criteria for diagnosing anaphylaxis can be found in Table 2.30,31
It is important to recognize the signs and symptoms of anaphylaxis in patients with a peanut allergy; many patients who present to the ED represent first-time reactions. Among patients with life-threatening symptoms on initial reaction, 71% will have similarly severe reactions in subsequent episodes (compared with 44% of patients whose first reaction was not life-threatening).3
TREATMENT, INCLUDING PATIENT EDUCATION
Currently there is no cure for peanut allergy, and no appropriate therapies yet exist to reduce allergy severity. Modest gains have been reported in raising tolerance threshold levels through peanut oral immunotherapy—a long, painstaking process.19,21,32 For now, treatment for peanut allergy is directed at controlling symptoms, once a reaction has occurred. Therefore, the clinician’s goal is to educate peanut-allergic patients and their families on avoiding accidental peanut ingestion, recognizing signs and symptoms of an allergic reaction, and preparing an emergency plan.4
Because four in five patients can expect peanut allergy to last for a lifetime,18,20 strict avoidance of peanuts and peanut products is essential—though difficult because of accidental exposure to food allergens (for example, when dining in restaurants or purchasing bakery products22,32), cross-contamination (as can occur when a food preparation area is not properly cleaned), and allergen cross-reactivity (such as consumption of other legumes).1 Patients must be taught to read food labels carefully for possible hidden sources of peanuts (see Table 37,8); in some cases, product labels bear helpful advisory wording, such as “may contain peanuts.”34,35 US legislation mandates that listed ingredients on food packaging include the eight foods that account for 90% of allergic reactions:
• Tree nuts
• Crustacean shellfish.34
Treatment for Anaphylaxis
In pediatric patients, administration of epinephrine is the definitive treatment for anaphylaxis; both the child and parents should carry an epinephrine self-injection device at all times in the event of accidental peanut ingestion. These devices are available in two strengths, based on the child’s weight, and expiration dates should be noted with care. Correct use of the epinephrine self-injection device should be reviewed at each office visit.6
Early-stage allergic reactions can be managed by oral antihistamines, such as diphenhydramine (1 mg/kg body weight up to 75 mg) and an intramuscular injection of epinephrine.1 Prompt transport to the ED should follow (see “Management of Anaphylaxis in the ED”1,9).
A 2010 expert panel on diagnosis and management of food allergy sponsored by the NIAID, NIH,3 does not advise women to restrict their diet during pregnancy and lactation. Similarly, the United Kingdom’s Department of Health and the Food Standards Agency (DHFSA)36,37 does not support the belief that eating peanuts and peanut-containing foods during pregnancy correlates with a child’s potential for developing a peanut allergy.
The DHFSA does recommend breastfeeding infants for the first six months, if possible, and that mothers refrain from introducing peanut-containing foods during that time. They also recommend that foods associated with a high risk for allergy be introduced into a child’s diet one at a time, to make it easier to identify any allergenic substance.36,37
Lastly, the DHFSA advises parents with a family history of peanut allergy to introduce peanuts only after consulting with their health care provider. The same consideration is advised if a child has already been diagnosed with another allergy.34 According to the American Academy of Pediatrics,6,38 children at high risk for food allergy (eg, atopic disease in both parents or one parent and one sibling) should be breastfed or be given hypoallergenic formula until age 1 year, with no solid foods before age 6 months; peanut-containing foods should not be given before age 3 or 4 years.
Peanut allergy can present a lifelong battle for affected patients. Eating one peanut or being exposed even to minute amounts of peanut protein could mean life or death without appropriate management. Reading food labels carefully, preparing peanut-free foods, recognizing the signs and symptoms of anaphylaxis, and obtaining the necessary treatment when allergic reactions occur are essential for peanut-allergic patients and their families.
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3. Boyce JA, Assa’ad A, Burks AW, et al. Guidelines for the diagnosis and management of food allergy in the United States: report of the NIAID-sponsored expert panel. J Allergy Clin Immunol. 2010;126(6 suppl):S1-S58.
4. Sicherer S, Muñoz-Furlong A, Godbold JH, Sampson HA. US prevalence of self-reported peanut, tree nut, and sesame allergy: 11-year follow-up. J Allergy Clin Immunol. 2010;125(6):1322-1326.
5. Hourihane JO, Aiken R, Briggs R, et al. The impact of government advice to pregnant mothers regarding peanut avoidance on the prevalence of peanut allergy in United Kingdom children at school entry. J Allergy Clin Immunol. 2007;312(5):1197-1202.
6. Nowak-Wegrzyn A, Sampson HA. Adverse reactions to foods. Med Clin North Am. 2006;90(1):97-127.
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10. Boughton B. New test for peanut allergy a step forward. www.medscape.com/viewarticle/740133. Accessed November 16, 2011.
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22. Sampson HA. Update on food allergy. J Allergy Clin Immunol. 2004;113(5):805-819.
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25. Du Toit G, Santos A, Roberts G, et al. The diagnosis of IgE-mediated food allergy in childhood. Pediatr Allergy Immunol. 2009;20(4):309-319.
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29. Sheffer AL. Allergen avoidance to reduce asthma-related morbidity. N Engl J Med. 2004;351(11):1134-1136.
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31. Sampson HA, Munoz-Furlong A, Campbell RL, et al. Second symposium on the definition and management of anaphylaxis: summary report—Second National Institute of Allergy and Infectious Disease/Food Allergy and Anaphylaxis Network symposium. J Allergy Clin Immunol. 2006;117(2):391-397.
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38. American Academy of Pediatrics. Committee on Nutrition. Hypoallergenic infant formulas. Pediatrics. 2000;106(2):346-349.