Food allergies affect up to 8% of children and 5% of adults, and prevalence appears to be increasing!
- Can appear at any age, but normally present in childhood
- More common in western and industrialized countries
The main culprits are peanuts, tree nuts, shellfish, cow’s milk, wheat, soy, and hen’s eggs.
- Cow’s milk allergy most common in infants and young children
- Peanut, tree nut, and shellfish allergies often persist into adult (<20% resolution during childhood)
Many food allergies resolve during childhood:
- Cow’s milk: >50% by 5-10yo
- Hen’s egg: ~50% by 2-9yo
- Wheat: 50% by 7yo
- Soy: 45% by 6yo
Increased risk of developing asthma if diagnosed with food allergy at a young age (O.R. 5-10 in prospective studies!)
Signs & Symptoms
Typically rapid onset (minutes) but can take up to a few hours (e.g., delayed meat allergy)
- Highest incidence in kids <4yo
- Most common triggers include food, drugs, and insect stings
- Typical onset within seconds/minutes. Biphasic reactions occur in 20-30% of cases, typically within 12 hours (but up to 72 hours!) For this reason, patients should carry 2 epinephrine autoinjectors at all times.
- Symptoms are variable!
- Skin/mucosa involvement: 90%
- Respiratory involvement: 70%
- GI involvement: 45%
- Cardiovascular involvement: 45%
Oral Allergy Syndrome (aka Pollen-Food Allergy Syndrome)
- Thought to be the most common food allergy in adults (up to 5–17%% of the general population in Europe), although can develop in childhood or adulthood
- Patients thought to develop allergic rhinitis first then food allergy second
- Symptoms occur minutes after eating certain raw fruit, vegetables, or nutes
- Symptoms are typically mild
- Pruritus, tingling, mild erythema, and subtle angioedema of the lips, oral mucosa, palate, and throat
- Symptoms normally resolve minutes after last exposure/ingestion and may not occur at all if culprit food is cooked
- Patients should be educated on cross-reactivity patterns:
Specialty referral should be considered for any suspected IgE-mediated food allergy!
Diagnosis is made with:
- History with consistent signs and symptoms
- Positive diagnostic testing (skin prick test or food-specific IgE immunoassay)
Key point: Positive testing without consistent history is insufficient (e.g., dust mite allergy can have positive serum IgE to shellfish)
Skin prick testing (SPT):
A positive SPT is a wheal that exceeds a negative control by ≥3 mm. SPT is performed in an office staffed to treat reactions with medication (e.g., epinephrine IM). It should not be used to screen patients with broad panels, and can’t be with some dermatological conditions (e.g., severe eczema).
Benefits of immunoassay testing include:
- Widely available
- Unaffected by presence of antihistamines or other medications
- Useful in patients with severe anaphylaxis (SPT has more risk)
- Useful in patients with dermatological skin conditions that preclude skin testing
- May be ordered by generalist
- Recommended in multiple settings:
- history of anaphylaxis
- history of difficulty breathing, throat tightness, or possible hypotension
- clinical judgment (trace, certain allergens, history of asthma, etc.)
- 7.5-25 kg: 0.15 mg
- 25 kg: 0.3 mg
- Clinical pearls:
- Check expiration dates!
- Store at room temperature
- Prescribe multiple autoinjectors, as needed (e.g., one for each parent’s home)
- If in doubt, administer epi!
- You can give a second dose if no improvement in 5-15 minutes
Desensitization therapy for food allergies is investigational at this time.
- Sublingual, subcutaneous, rectal, oral, non-specific therapies (Anti-IgE, Anti-IL4), etc.
Oral: daily ingestion of gradually increasing doses of food allergen until daily maintenance dose is achieve
- Goal: increase the allergic threshold
- Usually a single food
- Needs sustained therapy (lasts ~6 months after 3-5 years)
- Increased risk of anaphylaxis, other reactions, and need for epinephrine (Chu, et al., 2019)
Introducing Highly Allergenic Foods to At-Risk Infants
- Early introduction of peanut-containing foods in high-risk infants is safe AND 81% relative reduction in peanut allergy
2016: LEAP-On Study
- 4.8% developed allergies vs 18.6% in the avoidance group
Does your patient have suspected allergy or severe eczema?
- Egg allergy in 9% in treatment group vs 38% in placebo group
- Yellow fever and rabies vaccines are contraindicated
- Early introduction of 6 allergenic foods at 3 vs 6 months
- Allergies were less frequent in the early-introduction group (2.4% vs 7.3%)
- Did not affect breastfeeding rates
- Developmental readiness
- Try other foods first
- First exposure at home
Guidelines are evolving:
- Delaying introduction of highly allergenic foods does NOT prevent atopic disease
- Early exposure (4-6mo) to safe forms of peanut decreases risk of peanut allergy
- Data on other allergenic foods (including eggs) are less clear
- Refer to allergist for testing if severe atopic dermatitis or suspected food allergy
- Food allergies are classified as IgE-mediated and non-IgE-mediated food reactions
- Diagnosis is based on history plus diagnostic testing (SPT or immunoassay)
- Key to management is allergen avoidance and epinephrine prescription, if indicated
- Desensitization strategies can be considered with specialty referral
- Counsel parents on introduction of highly allergenic foods, as per current guidelines, based on risk stratification
Blog post based on Med-Peds Forum talk by Tamara Lhungay, PGY2, and Fritz Siegert, PGY3