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Shellfish Allergy: Overview, Diagnosis, and Treatment

About Shellfish Allergy

Shellfish is among the most common causes of food allergy.1 Worldwide prevalence of shellfish allergy was found to be 0.6 percent, with higher incidence reported in the Asia-Pacific region.1

The phyla of arthropods (crustaceans) and mollusks are generally referred to as “shellfish.”2 Patients with allergy to shellfish may fail to identify the offending seafood species, often due to confusion regarding the different names used to describe diverse seafood.2 Mollusks are a large and diverse group, including mussels, oysters, abalone, snails, and squid (calamari).2 Crustaceans include prawn (shrimp), crab, and lobster.2 Shellfish allergy is different than an allergy to finned fish, such as salmon or trout.

Shellfish allergy does occur in children but is more prevalent in adolescents and adults: 60 percent of patients with shellfish allergy first react during adulthood.3 Because shellfish allergy is often noted in adults, it is considered a life-long allergy that is not usually outgrown.3-5

Allergic reactions are generally immediate (within 2 hours), however, late phase reactions (up to eight hours after ingestion) have also been reported, particularly in shellfish-allergic patients.6 Reactions to snow crab, cuttlefish, limpet, and abalone are common causes of late-phase reactions.2 Patients may have a single symptom, but often there is a multi-organ reaction. Seafood allergy, including shellfish, has the potential for severe reactions, and in some cases, can lead to life-threatening anaphylaxis.2,3

60% of patients


Sixty percent of patients with shellfish allergy first react during adulthood.3
 

Common clinical manifestations of IgE-mediated seafood allergy appear similar to the symptoms experienced due to other foods and include:2,5

  • Urticaria
  • Angioedema
  • Flushing
  • Pruritus
  • Sneezing
  • Rhinorrhea
  • Congestion
  • Conjunctivitis
  • Shortness of breath
  • Wheeze
  • Cough
  • Nausea
  • Vomiting
  • Diarrhea
  • Gastrointestinal pain
  • Hypotension
  • Syncope
  • Sense of impending doom

Seafood allergy, including shellfish, has the potential for severe reactions, and in some cases, can lead to life-threatening anaphylaxis.2,3

Shellfish allergy: Refining differential diagnosis through testing

The current clinical approach to shellfish allergy diagnosis includes a physical examination, skin-prick testing, specific IgE testing, and, in selected cases, an oral food challenge.1 Like all food allergies, diagnosing a shellfish allergy starts with a physical examination and, of critical importance, a food-allergy-focused patient history.7,8

The findings of this shellfish-allergy-focused patient history can then be used to guide testing decisions and results interpretation. This systematic approach can help determine whether the reported history of food allergy, combined with laboratory data, is sufficient to diagnose shellfish allergy, or if an oral food challenge should be considered.1,9 

Who should be tested?

Identifying individuals with shellfish allergy is important, as these patients are at risk for severe reactions.2,3 As allergy to shellfish is usually lifelong, effective and accurate diagnostic workup for seafood allergy is essential for clinicians and patients.1,3-5

Click to View Algorithm

The evaluation for a patient with a possible food allergy begins with a thorough history and physical exam. If the clinical history suggests an IgE-mediated food allergy, skin-prick or specific IgE blood tests are needed to help confirm the diagnosis. Data from Niggemann and Beyer and Lopata et al.

Shellfish allergy and quality of life

Food allergy, including shellfish allergy, can have a dramatic effect on quality of life.10 Many studies have detailed the negative effect of food allergy on health-related quality of life (HRQoL), as well as the financial and emotional toll a food allergy takes.9 Identified issues include feeling different because of the diet, worrying about foods, the presence of physical and emotional distress, increased responsibility, effect on social activities (social restrictions, school, travel, and dining out), anxiety, stress, bullying, and having to consistently exercise greater caution.9

Common foods that may contain shellfish

Seafood allergens can be hidden in many products, such as:6

  • Surimi
  • Sauces (e.g., Worcestershire sauce, fish sauce)
  • Salad dressings (Caesar salad)
  • Asian and Greek dishes
  • Fish cake
  • Fish gelatin



The reuse of the same oil and pans to prepare shellfish dishes can be also an important source of hidden shellfish allergens. Patients with shellfish allergy should be careful when eating fried dishes at any restaurant that serves seafood.6

Cross-reactivity

The diagnosis of shellfish allergies is complicated by cross-reactivity between shellfish allergens and other arthropods.1 Due to the high cross-reactivity within shellfish groups, all patients with shellfish allergy are advised to avoid all shellfish.6 Of note, shellfish allergy in children is commonly associated with dust allergy and vice versa due to cross-reactivity.6 Special considerations should be made for shellfish-allergic patients due to the cross-reacting allergens present in shellfish and arthropods (e.g., dust mites, cockroaches), meaning that sensitization or immunotherapy with dust mites may provoke allergic reaction in these individuals.6

Testing Confidence

Testing Increases Diagnostic Confidence

Adding diagnostic testing to aid in a differential diagnosis has been shown to increase confidence in diagnosis to 90 percent.i,ii Conventionally, a diagnosis of allergic or autoimmune disease relies on the case history and a physical examination. However, adding diagnostic testing to aid in a differential diagnosis has been shown to increase confidence in diagnosis.i,ii Diagnostic testing can also help to improve the patient’s quality of life and productivity, reduce costs associated with absenteeism, and optimize use of medication, in addition to decreasing unscheduled healthcare visits.iii,iv 

i. Duran-Tauleria E, Vignati G, Guedan MJ, et al. The utility of specific immunoglobulin E measurements in primary care. Allergy. 2004;59 (Suppl78):35-41.
ii. NiggemannB, Nilsson M, Friedrichs F. Paediatric allergy diagnosis in primary care is improved by in vitro allergen specific IgE testing. Pediatr Allergy Immunol. 2008;19:325-331
iii. Welsh N, et al. The Benefits of Specific Immunoglobulin E Testing in the Primary Care Setting. J Am Pharm Assoc. 2006;46:627.
iv. Szeinbach SL, Williams B, Muntendam P, et al. Identification of allergic disease among users of antihistamines. J Manag Care Pharm. 2004; 10 (3): 234-238

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Management and care of patients with shellfish allergy

Currently, optimal management of seafood allergy does not exist. Management relies on the elimination of shellfish from the shellfish-allergic patients’ diet and symptomatic treatment of accidental allergic reactions.6 As manifestations of shellfish allergy may be life-threatening and are frequently life-long, patients with potentially life-threatening food allergy are generally prescribed an epinephrine autoinjector and educated in its use.5

Practice parameters have been developed to help guide the management and treatment of patients with food allergies, including shellfish.

References
  1. Tong WS, Yuen AW, Wai CY, Leung NY, Chu KH, Leung PS. Diagnosis of fish and shellfish allergies. J Asthma Allergy. 2018;11:247–260.
  2. Lopata AL, Kleine-Tebbe J, Kamath SD.Allergens and molecular diagnostics of shellfish allergy: Part 22 of the Series Molecular Allergology. Allergo J Int. 2016; 25(7): 210–218.
  3. Sicherer SH, Muñoz-Furlong A, Sampson HA. Prevalence of seafood allergy in the United States determined by a random telephone survey. J Allergy Clin Immunol. 2004 Jul;114(1):159-65.
  4. Wood RA: The natural history of food allergy. Pediatrics. 2003, 111 (6 Pt 3): 1631-1637.
  5. Abrams EM, Sicherer SH. Diagnosis and management of food allergy. CMAJ. 2016;188(15):1087–1093.
  6. Prester L. Seafood Allergy, Toxicity, and Intolerance: A Review. J Am Coll Nutr. 2016;35(3):271-83.
  7. Kurowski K, Boxer RW. Food allergies: detection and management. Am Fam Physician. 2008;77:1678-1688. 
  8. Burks AW, Tank M, Sicherer S, et al. ICON: Food allergy. J Allergy Clin Immunol. 2012;129:906-920. 
  9. Sicherer SH, Sampson HA. Food allergy: A review and update on epidemiology, pathogenesis, diagnosis, prevention, and management. J Allergy Clin Immunol. 2018 Jan;141(1):41-58
  10. Antolín‐Amérigo et al. Quality of life in patients with food allergy. Clin Mol Allergy. 2016;14:4