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Food allergy

Food allergies ( FA ) are immunologically mediated adverse reaction to foods.Food allergy is a major paediatric health problem in Western countries.

Prevalence ranges from 6-8 % in children up-to 3 yrs and is increasing Studies have shown that in Western countries challenge-diagnosed food allergy can be as high as 10 % with the greatest prevalence among young children It is also thought that the prevalence may be similar in developing countries Presence of food allergy – strongly correlated with other atopic disorders.

FA is an adverse reaction to a specific food antigen which is a immunologically mediated mechanism and happens in an individual who is susceptible to that specific allergen A complex interplay of which includes factors as 
○ epithelial barrier
○ mucosal and systemic immune response
○ route of exposure
○ microbiome Reactions classified as
○ IgE mediated or
○ Non-IgE mediated Mixed reactions – both IgE mediated and non IgE mediated can also be seen IgE mediated reactions → immediate type 1 hypersensitivity reactions Non IgE mediated → occur several hrs after allergen exposure Presence of food allergy – strongly correlated with other atopic disorders

Food allergy ( FA ) is different from adverse reactions which is a reaction caused by toxins or pathogens contained in the food 
they are also different from food intolerance’s which are non-immune reactions mediated by toxic , pharmacological, metabolic and undefined mechanisms These were often confused earlier It is important to point out that the underlying pathogenetic mechanism in FA is an adverse reaction arising from a specific immune response that occurs reproducible on exposure to certain food Same food can often be responsible for both intolerance and allergy posing diagnostic difficulties

More boys than girls are reported to have had reactions but more women reported reactions than men Seasonality – being born in spring or summer ↑ chances Family history is significant Infantile eczema is a major risk factor for IgE mediated food allergy Genetic , epigenetic and environmental factors Improved hygiene , antibiotic use , dog exposure Shift towards an urbanized lifestyle , migration

History and examination –Any personal h/o atopic diseases ( asthma , eczema , allergic rhinitis ) Any individual and family h/o atopic disease ( such as asthma , eczema or allergic rhinitis ) or food allergy in parents or siblings Details of any foods that are avoided and the reasons why Assessment of presenting symptoms ( see table ) and other symptoms that may be associated with food allergy including
○ age when symptoms first started
○ speed of onset of symptoms following food contact
○ duration of symptoms
○ severity of reactions
○ frequency of recurrence
○ setting of reaction ie at school or home etc
○ reproducibility of symptoms on repeated exposure
○ what food and how much exposure to it causes reaction Who raised the concern and suspects food allergy Suspected allergen Feeding history
○ age when weaned
○ breast-fed or formula fed
○ if being breast fed consider mother’s diet Previous treatment , response Examine
○ growth and physical signs of malnutrition
○ signs indicating allergy-related conditions as
 ♦ atopic eczema
 ♦ asthma
 ♦ allergic rhinitis 


IgE mediated

Skin Pruritus Erythema Acute urticaria ( localized or generalized) Acute angioedema ( most commonly in lips and face and around the eys )
Gastro-intestinal –Angioedema of the lips , tongue or palate Oral pruritis Nausea Colicky abdominal pain Vomiting Diarrhoea

Respiratory tract –Upper respiratory tract symptoms – nasal itching , sneezing , rhinorrhoea or congestion ( with or without conjunctivitis )
 Lower resp tract symptoms -cough , chest tightness , wheezing or shortness of breath

Signs or symptoms of anaphylaxis or other systemic allergic reactionsSkin testing- includes
○ Prick testing – most common screening test for food allergy ( negative predictive accuracy exceeds positive predictive accuracy )
 ♦ Out patients setting
 ♦ Epicutaneous introduction of allergen extracts with a standardised lancet
 ♦ Weal > 3 mm in dia is +ve
 ♦ May fail to show sensitization if antihistamines have been used
 ♦ Can take days or weeks for results
○ Intradermal testing -can induce systemic reaction so generally avoided
○ Patch testing- promising but additional studies needed
 so not recommended yet
 Blood tests for 
○ Specific IgE antibodies – has pitfalls
♦ positive results denote sensitization and may not confirm clinical allergy
♦ Not available for some food hypersensitivities 
♦ Diagnostic performance characteristics of specific IgE testing poor in case of fruits and vegetables
♦ Results available within 15 mins
○ Basophil histamine-release assays – limited availability ( research setting )

Not recommended ( NICE )
 Atopy patch testing Oral food challenge

Non-IgE mediated
Skin-Pruritus Erythema Atopic eczema
Gastrointestinal –GORD Loose or infrequent stools Blood and/or mucus in stools Abdominal pain Infantile colic Food refusal or aversion Constipation Perianal redness Pallor and tiredness Faltering growth plus one or more of GI symptoms above ( with or without sig atopic eczema ) -Elimination of suspected allergen -> for 2-6 weeks ( reintroduce following trial )
 Dietitian – referral-What foods and drinks to avoid How to read interpret food labels Alternative sources of nutrition Safety and limitations of an eliminated diet Information about future food reintroduction procedure Safety and limitations of oral food challenge reintroduction procedure

Referral-Faltering growth in combination with one or more GI symptoms
( see table ) No response to single-allergen elimination diet Had one or more acute systemic reactions Had one or more delayed systemic reactions Confirmed IgE-mediated food allergy and concurrent asthma Significant atopic eczema where multiple or cross-reactive food allergies are suspected Persistent parental suspicion of food allergy despite a lack of supporting history Strong clinical suspicion of IgE mediated food allergy but allergy test results are negative Clinical suspicion of multiple food allergies

References-

  1. Sicherer SH, Sampson HA. Food allergy: A review and update on epidemiology, pathogenesis, diagnosis, prevention, and management.J Allergy Clin Immunol. 2018;141(1):41‐58. doi:10.1016/j.jaci.2017.11.003 ( Abstract )
  2. Loh, Wenyin, and Mimi L K Tang. “The Epidemiology of Food Allergy in the Global Context.” International journal of environmental research and public health vol. 15,9 2043. 18 Sep. 2018, doi:10.3390/ijerph15092043
  3. Food allergy in under 19s: assessment and diagnosis Clinical guideline Published: 23 February 2011 www.nice.org.uk/guidance/cg116
  4. NICE Food allergy Quality standard QS118 March 2016
  5. Food allergy : a practice parameter update American Academy of Allergy , Asthma and Immunology
  6. The RCPCH care pathway for food allergy in children : an evidence and consensus based national approach Archives of Disease in Childhood Volume 96 , Issue Suppl 2
  7. Allergy care pathways for children : food allergy Royal College of Paediatrics and Child Health February 2012
  8. Food Allergy and Food Intolerance Patient UK
  9. Diagnosis of immediate food allergy BMJ 2014;349:g3695
  10. Food allergy BMJ 2011 ; 342:d933
  11. Diagnosis and assessment of food allergy in children and young adults in primary care and community settings: NICE clinical guideline Br J Gen Practice 2011 ;61(588):473-475
  12. Food allergy in children and young people: Evidence Update May 2012
  13. Food allergies Medscape Scott H Sicherer et al May 2016
  14. NICE Pathways – Food allergy in under 19s overview
  15. New Perspectives in Food Allergy Massimo De Martinis 1,2,* , Maria Maddalena Sirufo 1,2 , Mariano Suppa 3 and Lia Ginaldi 1, Int. J. Mol. Sci. 2020, 21, 1474; doi:10.3390/ijms21041474

 

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