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food allergy

Introduction

immunoglobulin E (IgE)–mediated food allergy, the most common type of food allergy, often develops early in life, lasts a lifetime and can be life threatening and cause anaphylaxis
peanut and tree nuts are two of the most common foods that cause allergic reactions, and are the most persistent and dangerous, with the highest lifetime risk for anaphylaxis.
6–10% of children and around 2–6% of adults have food allergy, most of which is IgE‑mediated
2-3.5% of children have peanut allergy and this represents a doubling of the rate in Western countries over a decade. Rates are also rising in Africa and Asia.
it appears certain ingested parts of proteins (eg. corn, wheat, soy epitopes) can bind to intestinal Treg immune cells to create an anti-inflammatory modulatory effect which usually induces tolerance.¹⁾

Most common IgE–mediated food allergens

the following account for 90% of IgE-mediated food allergens
peanuts - 2-3.5% children, 0.6% in adults
tree nuts (e.g. walnut, hazelnut, cashew) - 1–1.5% in children and 1% in adults
cow's milk - 1–3% of young children; much lower in adults as many outgrow it
- NB. this is different to cow's milk intolerance due to lactose intolerance which is a gut lactase enzyme issue
hens eggs - 1–2% of young children; many outgrow in later childhood
wheat - under 1% each in most studies, more common in early childhood and often outgrown
soy - under 1% each in most studies, more common in early childhood and often outgrown
fish - 0.9% in children and 0.5% in adults
shellfish (crustacean and mollusc) - 0.8% in children and 1.6% in adults
sesame - relatively low overall prevalence but a leading cause in some regions (e.g. Israel) and often persistent

Risk factors

risk appears to be mainly related to a mix of genetics, the GIT microbiome, skin factors and delayed exposures
major factors:²⁾
- early life antibiotic use
- self-identification as Black
- early onset of allergic conditions (atopic march or diathesis, atopic dermatitis (AD), rhinitis, asthma or wheezing)
- elevated skin transepidermal water loss
- parental migration before birth
  - a 2016 Australian study showed Australian-born children of Asian descent were more likely to have nut allergy than non-Asian children, children born in Asia who migrated to Australia were at decreased risk and that migration from Asia after the early infant period appears to be a protective factor against the development of nut allergy ³⁾
- delayed introduction of solid foods after 12 months of age
  - risk of the development of peanut allergy was 10 times as high among Jewish children in the United Kingdom as it was in Israeli children of similar ancestry. This observation correlated with a striking difference in the time at which peanuts are introduced in the diet in these countries: in the United Kingdom infants typically do not consume peanut-based foods in the first year of life, whereas in Israel, peanut-based foods are usually introduced in the diet when infants are approximately 7 months of age, and their median monthly consumption of peanut protein is 7.1 g⁴⁾
  - LEAP study⁵⁾ suggests early peanut consumption was associated with an 86% reduction in peanut allergy at 60 months of age among participants who had had negative results on a peanut-based skin-prick test at study entry and with a 70% reduction among those who had had positive test results at study entry
- family history of food allergy or related allergies
minor factors:
- filaggrin gene sequence variations
- male sex
- cesarean delivery
- firstborn status
factors with low certainty of being an important risk factor:
- facial AD lesions
- AD affecting beyond the flexural folds
- exposure to pollutants
- social history (eg, higher parental education, having a general [primary care] physician, family history of farming)
- birth-related factors (eg, preeclampsia, increased duration of ruptured membranes)
- maternal intake of acid suppressant medication during pregnancy
- maternal use of antibiotics during the postnatal period
- maternal intake of allergenic foods and nutrients during pregnancy and the postnatal period
- maternal depression during pregnancy or the postnatal period
- delayed introduction of other solid foods (eg, meat, cabbage, bread, carrots, soy)
- presence of a dog or cat at home
- pacifier sanitization by antiseptic
- household peanut protein (environmental exposure to allergen)
- metabolic biomarkers (eg, low vitamin D in children, high vaccenic acid)
- genetic biomarkers (C11orf30 [EMSY] variant LRRC32, SPINK5 variant rs9325071, MALT1 variant rs57265082)
- elevated ratio of infant gut Enterobacteriaceae to Bacterioidaceae relative abundance
factors NOT increasing risk:
- low birth weight
- postterm birth
- maternal age
- breastfeeding promotion
- maternal stress during pregnancy

Risk reduction measures

prevention of development of allergy:
- early introduction of solid foods before age 12 months
  - infants with severe eczema, egg allergy, or strong family history should introduce peanut (and sometimes egg) as early as 4-6 months, ideally after pediatrician consultation.⁶⁾
  - offer one new allergen per meal in age-appropriate forms (e.g., thinned peanut butter, well-cooked egg), in the morning for observation
  - never give whole nuts to an infant or young child - they are a choking hazard until age 5
- avoidance of unnecessary antibiotics in early life
- an hypothesis suggests allergy development via food contact with damaged skin (eg. eczema) so perhaps avoid this
risk reduction once it has developed:
- strict avoidance of precipitant - may need allergy testing to ascertain
- patient to have an EpiPen on hand at all times
- patient and family education
- in Victoria, there is mandatory reporting of food allergies to the government in an attempt to reduce fatalities at schools, etc
- consider desensitisation immunotherapy to develop tolerance
  - eg. peanut oral immunotherapy
    - peanut allergy occurs in ~2% of children in Western countries
    - initial oral dosing with supervision, then using 30mg or 300mg maintenance doses generally develops tolerance to accidental exposures and the 30mg dose appears to be as effective with less side effects than the standard 300mg dose of peanut ⁷⁾