Definition
l Adverse food reaction : any abnormal reaction after
the ingestion of a food
l Food intolerance : adverse physiologic response
l Food hypersensitivity (allergy) : adverse immunologic
reaction
l Food aversion : mimic adverse food reactions but not
reproducible when the patient
ingests the food in a blinded fashion
Prevalence
l children younger than 3 years : 6%
l adults in the United States : 2%
l 2.5% of newborn infants : hypersensitivity reactions
to cow milk in the first year of life
l 1.5% of young children : allergic to eggs
l 0.5% of young children : allergic to peanuts
Pathogenesis
l developmental immaturity of various components of the
gut barrier and immune system
l oral tolerance : unresponsiveness of T cells to ingested
food proteins
dendritic cells : express IL-10, IL-4, which favor
generation of tolerance
T regulatory cells : potent sources of TGF-beta
gut flora
l traditional or class 1 food allergy : sensitization
to food allergens after the ingestion
of a food
l class 2 food allergy : after inhalation of an airborne
allergen that cross-reacts with a specific
food
l in children : cow milk, egg, peanut, soy, wheat, fish
l in adults : peanuts, tree nuts, fish, shellfish Diagnosis
l medical history
the food responsible for the reaction
the quantity of the suspected food ingested
the length of time between ingestion and development
of symptoms
whether similar symptoms occurred when the food
was eaten previously
whether other factors (eg, exercise) are necessary
when the last reaction to the food occurred
l dietary diaries
l elimination diets
l skin prick tests
l radioallergosorbent tests
l double-blind, placebo-controlled food challenge (DBPCFC):
gold standard
l open or single-blind challenges
Treatment
l strict elimination of the offending allergen : the
only proved therapy
l education of patients and their families
to avoid accidentally ingesting food allergens
to recognizedearly symptoms of an allergic reaction
to initiate early management of an anaphylactic
reaction
l antihistamines : partially relieve symptoms of OAS,
IgE-mediated skin symptoms but do not block systemic reactions
l oral corticosteroids
l American Academy of Pediatrics recommends
"high-risk" infants be exclusively breast-fed
lactating mothers avoid peanuts and nuts (to avoid
sensitization through breast milk)
the introduction of solid food be delayed until
6 months of age
major allergens, such as peanuts, nuts, and seafood,
be introduced after 3 years of age
l wheal and flare reaction following external
contact with a substance
l it usually appears within 30 min, and clears completely
within hours, without residual signs of irritation
l Classification
Nonimmunological contact urticaria
Immunological contact urticaria
Mixed/undetermined contact urticaria
Nonimmunological contact urticaria (NICU)
l produce a reaction without any previous sensitization
in most or almost all exposed persons
Pathogenesis
l not clearly understood
l appears to involve the release of vasogenic mediators
without involvement of immunological processes
Dimethyl sulphoxide (DMSO)
- damage blood vessels, making them leaky
- cause mast cell degranulation
sorbic acid, benzoic acid : release of prostaglandin
D2 without concomitant histamine release
Diagnosis
l closed patch test - patches
are removed after 15 min and reactions read at 20, 40,
60 min l open test - carried
out on the arm or upper back, with most reactions evident
by 45 min - erythema and
edema have been mainly visually
Immunological contact urticaria (ICU)
l Type 1 hypersensitivity reaction, mediated by allergen-specific
IgE in a previously sensitized individual
l contact urticaria syndrome : potential for multisystem
involvement
Pathogenesis
l allergen penetration through the epidermis, then binding
to IgE on mast cells
l causing degranulation and release of histamine and other
vasoactive substances
l other inflammatory mediators such as prostaglandins,
leukotrienes and kinins may also influence
the clinical response
Diagnosis
l skin prick tests with fresh foods or commercially available
reagents
l measurement of allergen specific IgE
l open application test
Treatment
l allergen avoidance
l antihistamine therapy for mild reactions
l self-administered adrenaline device for those with
life-threatening reactions
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