July 13, 2004 -- Shrimp, lobster, clams: Americans love seafood. But many adults will develop a severe allergy to shellfish as well as tuna and salmon.
Some 7 million Americans are thought to be affected, or 2.3% of the population, according to a nationwide survey.
"This study showed that seafood allergy often develops in adulthood, that most persons have multiple reactions, and that reactions often include severe symptoms," writes lead researcher Scott H. Sicherer, MD, with the Mount Sinai School of Medicine in New York.
His study appears in this month's issue of the Journal of Allergy & Clinical Immunology.
Researchers define "seafood" as finned fish (tuna, cod, salmon) and shellfish (shrimp, crab, lobster, scallops, clams, squid). An allergic reaction to certain proteins in seafood can cause life-threatening anaphylaxis -- a sudden, severe, potentially fatal reaction that results in low blood pressure and throat swelling, making breathing difficult. Seafood allergies can also cause a severe skin reaction or can trigger an asthma attack.
Despite the potential lethal nature of the reaction, few studies have looked at exactly how common seafood allergy is, Sicherer says.
His nationwide telephone survey involved almost 15,000 adults who answered detailed questions about finfish and shellfish -- identifying individuals in their homes who had a seafood allergy, including positive allergy skin test reaction or blood tests or an allergic reaction from eating fish. The volunteers also produced information on the ages when these reactions first occurred.
Sicherer found that both fish and shellfish allergies were more commonly found among adults ages 40 to 60. Also:
- 6% of households had at least one person with a seafood allergy.
- 3% of adults had any seafood allergies, compared with 0.6% of children.
- 4% of women had seafood allergies, compared with 2% of men.
- 40% of fish allergies and 60% of shellfish allergies began in adulthood.
- For about 10% of those surveyed, the worst reactions were caused by touching or smelling fish.
- Hives, swelling, difficulty breathing, and tightened throat were the most common symptoms.
- Salmon, tuna, catfish, and cod were the fish that most commonly caused reactions.
- Shrimp was the most common type of shellfish that caused reactions.
Only 9% of allergic people in Sicherer's study had a prescription for epinephrine, which halts the reaction. Yet 16% reported having been given the medication to halt an allergic reaction to fish in the past. "This discrepancy highlights the need for improved awareness and education about seafood allergies," he writes.
Since many people surveyed were reporting allergic reactions but were not actually tested for a food allergy, his results may be somewhat conservative, he says.