Shellfish allergy is one of the most common food allergies worldwide and the third most common in US children. A recent study (published in Journal of Allergy and Clinical Immunology November 2019) was done to assess the prevalence of it in the United States. Overall the estimated of shellfish allergy was 2.9% and where the physician confirmed it was 1.2%.
Overall shellfish allergy was found to affect nearly 3% of US adults, half of whom developed it during adulthood. Adult mollusk (clams, oysters, mussels, scallops) allergy was 1.6%, significantly lower than the estimated crustacean (lobster, shrimp, scallops, crab) allergy.
Nearly half of shellfish allergic adults report visiting the emergency for food allergy treatment within their lifetime, not all adults with shellfish allergy experience severe reactions. More than 40% of shellfish allergic adults report only mild to moderate reactions. Interestingly crustacean allergic patients report more skin/mucosal symptoms and wheezing compared to mollusk allergic patients, who report more gastrointestinal symptoms.
In this study, 46% of crustacean-allergic adults were also mollusk-allergic, previous studies showed 14%, so it is a lot higher. The other way showed that 70% of mollusk allergic patients were crustacean allergic, suggesting greater cross reactivity between crustacean and mollusk allergens than previously acknowledged. Nearly 20% of those with shellfish allergy had comorbid fin fish allergy (tuna, salmon, cod, flounder, etc).
Shellfish allergy (crustaceans and mollusks) are one of the top 9 allergens in addition to milk, wheat, soy, eggs, peanuts, tree nuts, sesame and fish. Many of the child food allergens (wheat, milk, soy and eggs) can be outgrown, but the others persist and can be lifelong.
Recent studies have shown that early introduction of peanuts can prevent one from developing an allergy to it. New Peanut Guidelines There have been no formal studies on how to prevent seafood allergies as most of the time they are acquired in adulthood. More studies will need to be done to understand in how to prevent them.
The treatment of choice for anaphylactic food reactions is epinephrine. If one is allergic to seafood, one should always carry around injectable epinephrine in case of accidental exposure.