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The Seafood Section

Shellfish and Fish Allergies Explored

From the Allergic Living Archives.

A quick test: what’s the most widespread food allergy in North America today?

If you answered ‘peanut’, that’s incorrect. But you could hardly be blamed given that legume’s notoriety. The right answer is seafood – from fish to crustaceans and mollusks.

At a time when every “must-try” new restaurant is an over-priced sushi bar, an astounding 2.3 per cent of Americans are now allergic to one form or another of seafood. (There is no such specific Canadian data, but general rates of allergic prevalence are considered comparable.)

If that incidence comes as a surprise, however, you’re in good company. Even the researchers who surveyed 5,500 households for the Food Allergy & Anaphylaxis Network (now FARE) in Virginia and the Mount Sinai School of Medicine in New York to arrive at this finding were taken aback.

“We said, ‘can this be real?”‘ recalls Anne Munoz-Furlong, founder and former CEO of FAAN and co-author of the resulting seafood prevalence study published in 2004. “We learned that shellfish and fish is about double the incidence of peanut and tree nut combined.”

In fact, the researchers reviewed the data to see if something was, well, fishy. But it wasn’t. Those who were accepted as allergic in the detailed phone survey “were very clear in their answers and the symptoms were very clear,” says Munoz-Furlong. Supporting those findings was a 15-nation study that showed similarly high levels of seafood allergies.

Shrimp was the most common cause of reactions in the FAAN-Mount Sinai survey. In fact, shellfish as a group – crustaceans and mollusks – proved by far the larger cul­prit, with 2 per cent of survey participants reporting shellfish allergy while 0.4 per cent reported fish.

Another eye-opening finding was that this is largely an adult phenomenon. The survey found 2.8 per cent of adults were seafood allergic compared to 0.6 per cent of children. And that can be one of the most difficult aspects of this condition – since it strikes grownups, who’ve been eating for years as they pleased, they often don’t know what hit them.

What happened to Chris Oleson is not uncommon. The 41-year-old is a self‑described “beach guy” who lives in San Francisco and grew up surfing on the California coast.

One day in 2002, he was with his wife Julia at an upscale sushi restaurant. He’d eaten about five or six very tasty” items from the trays on offer, when a waiter approached. “Sir, your ears are turning red. You may want to get that checked out,”‘ Oleson recalls him saying.

Oleson was suddenly rather feverish and unwell, but he wasn’t that concerned. He and his wife just thought he was com­ing down with a bug and had better get home. Oleson has asthma, and on the drive home an attack started coming on. He was also feeling woozy when Julia said, “you know, you’ve got hives.”

By the time they got through the door at a nearby hos­pital, Oleson was staggering. He lost consciousness on a stretcher. “The last thing I remember was they took my blood pressure and said, ‘this guy’s lucky to be alive’ It was very, very low.”

Oleson saw an allergist for allergy skin and blood tests. He turns out to be part of a minority allergic to both shellfish and finned fish (though his shellfish sensitivity measures much higher).

What he realizes today is that this was actually his second seafood reaction. The first came eight months earlier, at a gathering at his in-laws home in Washington state. The so-called “bad flu” he suffered had overcome him right after a dinner of fresh cooked lobster. While he’d eaten crab all his life, that was his first experience eating lobster.

Those who suddenly find themselves allergic wonder: what causes a seafood allergy to switch on in adulthood?

“No one knows for sure,” says Dr. Scott Sicherer, an allergist and associate professor of medicine at Mount Sinai. Sicherer is a co-author of the U.S. prevalence survey and also has written a two-part review of seafood studies from around the world,  published in 2006 in UpToDate, an evidence-based clinical information resource for physicians.

While there are no firm answers as to “why,” he identifies a couple of theories. Scientists are intrigued that the main allergen in shellfish, the muscle protein tropomyosin, is very similar to the tropomyosin found in dust mites and cockroaches, highly allergenic pests.

“One theory would be air exposure to these [insect] proteins could drive a shell­fish allergy,” says Sicherer, which might explain studies in which orthodox Jews, who had never eaten a crustacean, tested positive to shellfish.

But like most allergy theories, this one has holes: how to resolve, as Sicherer notes, that “the vast majority of people testing positive to dust mites are fine eating shellfish?”

Another hypothesis is that adults who become allergic eat seafood on occasion rather than regularly, and that may affect their tolerance.

“For example,” Sicherer says, “we have seen some people re-develop a peanut allergy when they did not consume [peanut] for about a year after tolerating it in a doctor-supervised feeding test. Maybe not having these foods in the diet routinely allows the immune system to misdirect its responses – sort of forgetting that the food is `innocent’.”

The key allergic proteins in fish and shellfish are unrelated – so people are usu­ally only allergic to one or the other seafood group. But if you’re highly allergic to shrimp and want to try eating a fish not in your diet, Sicherer recommends speak­ing to an allergist first and probably testing “to avoid surprises.”

He sees another confounding aspect of these allergies: there can be a great variability of triggers from person to person. You might, for instance, be allergic to caviar (fish eggs) of a fish, but not the fish’s meat.

In his review of studies, he noticed that those who com­monly reacted to freshly prepared fish usually did not react to canned salmon and tuna. “To make it more complicated, the part of the fish could matter,” he says.

But what you can safely consume with a seafood allergy often depends, not only science, but on food preparation methods.

Allergic? What You Can Do

“Looking at our fatality data, we can see the risk of having a fatal reaction in a restau­rant is higher than anywhere else where you might be eating food,” says Munoz-Furlong. And what do adults do all the time for business and socializing? They eat out.

The founder of FAAN says adults with seafood allergy should be able to carry on their lives as they were before diagnosis – except that they do have to learn the allergy basics: from reading food labels to always carrying epinephrine, and being highly selective of where they choose to dine.

She counsels against seafood houses. Then, once the allergic person has picked a restaurant that’s allergy-aware and light on seafood, she advises thoroughly informing the server of the condition, and avoiding sauces and fried foods – since you won’t know what’s in a sauce or what has been in that oilor on that grill.

Muňoz-Furlong is concerned that many seafood allergic adults are too cavalier, that they haven’t adjusted to the seriousness of allergic disease – and many don’t follow those basic allergy rules. “Most adults think they can manage their allergy in a restaurant,” she says.

“But does the cook get the message? Have the prep areas been sep­arated so there’s no cross-contact?” The risks “are because of the mistakes other people will make on your behalf, not the mistakes you’re going to make.” The preva­lence survey also showed an alarming number of these adults do not even own epinephrine auto-injectors.

Oleson is an example of someone with seafood allergy who gets it: he carries a kit with two auto-injectors, asthma coeds and Benadryl, and also has a kit in his car. He remembers his big scare clearly, and sure doesn’t want that to happen again.

The biggest challenge he has faced? “I had a rough time with some of the family,” he says with a note of sadness. One set of rel­atives is upset with him for no longer visiting despite the fact that they live “in the middle of nowhere and a hospital is 80 miles away.”

A skeptical brother-in-law even tried to serve him shrimp at a dinner. “It’s hard to understand other people who don’t understand,” he says.

Given his reaction history and asthma and the fact that he has had minor inhalant reactions at markets where crabs are being cooked, Oleson no longer eats out. Living in a capital of seafood cuisine, it’s not easy to locate a safe restaurant. But Oleson and his wife often have friends over instead, and he hasn’t stopped living because of seafood avoidance. “Learning to balance a new lifestyle is what allergy is for me.”

He’s also clearly kept a sense of humor, joining Allergic Living’s website forum as “surferdude” and introducing himself with a hearty “cowabunga dudes and dudettes!” Reminded of this, he chuckles. “You’ve got to have a sense of humor. You’ve got to take life with a grain of salt sometimes.”

For Cross-Reactions within seafood groups, read: Fast Facts About Seafood Allergies

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