40 percent of fish-allergic children selectively tolerant to fish

Forty percent of fish-allergic children are selectively tolerant to fish, particularly species with lower β-parvalbumin levels, while 41 percent of those with fish and shellfish cosensitization can tolerate crustaceans, mollusks, or both, a real-world study in Hong Kong reports.

The Chinese University of Hong Kong (CUHK) research team therefore developed a fish allergenicity ladder based on gradient of immunoglobulin E (IgE) sensitization, which corresponded to β-parvalbumin levels of fish, to guide diagnosis of fish allergy and minimize the risk of adverse reactions during oral food challenges (OFCs). [J Allergy Clin Immunol Pract 2024;12:633-642.e9]

“In clinical practice, patients with an allergic reaction to one type of fish are often advised complete avoidance of fish due to cross-sensitization to fish from other families and high rates of false positivity with conventional allergy tests,” said Dr Agnes Leung of the Department of Paediatrics, CUHK. “Avoidance of crustaceans and mollusks is also a common practice among families with fish-allergic children due to fear of cross-reaction.”

In the current study, the researchers recruited 249 paediatric patients with IgE-mediated fish allergy from six allergy clinics in Hong Kong between July 2016 and December 2021. Enrolled at a median of 2.2 years after their initial fish-allergic reactions, the participants (median age, 4.2 years; male, 66 percent; atopic dermatitis, 95 percent; allergic rhinitis, 56 percent; additional food allergies [other than fish, crustaceans or mollusks], 58 percent; carried autoinjectors, 46 percent) underwent skin prick tests and evaluation of specific IgE levels to various species of fish and shellfish. Detailed clinical history, including recent seafood consumption, was documented. OFCs were performed for 75 participants who provided voluntary consent.

Carp (grass carp and mud carp) was most commonly involved (38 percent) in the participants’ first allergic reaction to fish, while grass carp was most commonly involved in positive OFCs (49 percent).

“Levels of fish-specific IgE were higher against species with higher β-parvalbumin levels than those with lower β-parvalbumin levels [p<0.001],” the investigators reported.

A fish allergenicity ladder was therefore developed based on gradient of IgE reactivity, which corresponds to β-parvalbumin levels of fish:

·      Highest allergenicity and β-parvalbumin content: tilapia, catfish and grass carp;

·      Intermediate allergenicity and β-parvalbumin content: grouper and herring;

·      Lowest allergenicity and β-parvalbumin content: cod, halibut, salmon and tuna.

“Notably, 40 percent of fish-allergic participants, including 46 percent of challenged and 27 percent of nonchallenged participants, indicated tolerance to certain fish species, ranging in number from 1 to 16,” the investigators pointed out. “The most common fish species to which they demonstrated tolerance were salmon [28.5 percent], tuna [9.2 percent], and halibut [8.0 percent].”

Cosensitization to shellfish was noted in 52 percent of fish-allergic participants. However, 41 percent of participants with shellfish and fish cosensitization reported tolerance to crustaceans (8 percent), mollusks (15 percent), or both (18 percent).

In contrast, 33 percent of fish-allergic participants who lacked shellfish cosensitization avoided both crustaceans and mollusks.

“Our study provides evidence that a considerable proportion of fish-allergic individuals exhibits selective tolerance to fish with lower allergenicity, and many may tolerate shellfish. These findings underscore the importance of developing precise diagnostic strategies and providing clinical advice based on evidence from tests to reduce unnecessary seafood avoidance,” said Professor Ting-Fan Leung of the Department of Paediatrics, CUHK.