(Reuters Health) - A small study of children and adults in Canada suggests that fish and shellfish allergies don’t usually resolve over time.

Together with nut allergies, fish and shellfish sensitivities are the biggest causes of severe allergic reactions, the study team writes in The Journal of Allergy and Clinical Immunology: In Practice. But little is known about how long these seafood allergies last.

“Fish and shellfish allergy . . . accounts for the majority of life-threatening (anaphylaxis) reactions in adults but has attracted much less research attention than other food allergies, such as peanut,” senior study author Dr. Moshe Ben-Shoshan told Reuters Health by email.

Patients need to understand the likely course of their food allergy and so far there are no data on the natural resolution of this important allergy, said Ben-Shoshan, a pediatric allergist at McGill University Health Center in Montreal.

“Hence our group with the support of AllerGen NCE aimed to address for the first time this important knowledge gap,” Ben-Shoshan said.

Data from Canada and the U.S. suggest that about 0.5 percent of adults and up to 1 percent of children are allergic to fish. And anywhere from 1.4 percent to 2.5 percent of adults and 0.5 percent to 2 percent of children are allergic to shellfish, the authors note.

To see how common it is for these allergies to go away, Ben-Shoshan and his colleagues recruited 63 patients, including 37 with allergies to fish, 25 with allergies to shellfish, and one with allergies to both.

Study participants or their guardians were asked to fill out surveys that included questions about their initial and most severe reactions to fish or shellfish, plus allergy symptoms such as rashes, itching, runny nose, coughing abdominal pain, nausea, and difficulty breathing. Researchers also reviewed medical records.

The most common allergy-inducing fish was salmon, affecting about 18 percent of those with fish allergies. Shrimp was the most common allergy-inducing shellfish, affecting about half of the participants with shellfish allergies.

After following kids and adults with seafood allergies for up to six years, researchers found that each year, less than 1 percent saw their allergy resolve.

A food allergy was considered to be resolved if the patient was able to tolerate seafood at least once a week or if their doctor had diagnosed the allergy as resolved.

“Seafood allergy rarely resolves - less than 1 percent resolution rate for either fish or shellfish allergy per year of follow up,” Ben-Shoshan said.

The study is limited due to its small size, the authors note.

“It is crucial to conduct studies to assess factors that can predict resolution as well as explore protocols that can induce tolerance in those that have shellfish allergy,” Ben-Shoshan said.

SOURCE: bit.ly/2yb86gn The Journal of Allergy and Clinical Immunology: In Practice, online September 22, 2018.