The boy had no history of allergies. He received blood products including plasma and chemotherapy as part of his treatment for medullobastoma, a type of brain tumour.
In Monday's issue of the Canadian Medical Association Journal, Dr. Julia Upton of the Hospital for Sick Children in Toronto and her team describe how the boy experienced anaphylactic symptoms including swelling of the lips, facial redness, throat discomfort and fatigue within 10 minutes of eating salmon, a food he'd eaten often before without having an allergic reaction.
The symptoms resolved after a few hours of treatment with an antihistamine. The boy was told to avoid salmon and given a prescription for an epinehphrine autoinjector as a precaution.
Doctors suspected analyphylaxis from transfer of an allergy antibody in blood plasma that can react against allergens in rare cases, rather than the typical scenario where a person makes the allergy antibodies themselves.
"It's rare to have an allergic reaction to a previously tolerated food," said Upton, a staff physician in Sick Kids' clinical immunology and allergy department. "It's extremely rare to have a new allergy come from a blood product. Thankfully, the prognosis is excellent and it typically resolves within a few months."
Researchers said unusual causes of food allergy should be suspected in children who react to previously tolerated foods.
When this type of passive transfer of allergies after blood transfusion is suspected, the hospital's transfusion service can investigate donors to determine if they can continue to be suitable blood donors.
The researchers advised doctors to followup with the family after a few months to decide when to reintroduce the temporary allergen into the child's diet.
In the boy's case, four days after the fish reaction, he experienced an allergic reaction to peanuts minutes after eating a chocolate peanut butter cup. Again, he'd often eaten peanut products before.
At that point, the hospital did skin prick tests, which were positive for fish, peanut and tree nut.
When the boy's family was contacted about six months after his reactions, the boy was again eating salmon and peanuts. At Upton's last contact with him a few months ago, he was better.
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