There were 5162 patients seen in the A/I clinics of the TMC in the 13 years between January 1, 1997 and January 30, 2010. Of these, 640 (12.4%) had physician-recorded food allergy. Of the A/I clinic patients with food allergy, 159 (24.8%) had seafood allergy, giving a prevalence of 3.08% in the total allergy clinic population. Nine seafood-allergic adults of 159 (5.66%) reported both shellfish and fish allergy. Fifty-nine percent were only allergic to shellfish (n = 94/159) with 13.8% (n = 22/159) allergic only to fish. Thirty-four (21.4%) had unspecified seafood allergy (). Of the entire A/I clinic population, 1.8% (94/5162) had only shellfish allergy, 0.43% (22/5162) had only fish allergy, 0.17% (9/5162) had combined shellfish/fish allergy, and 0.66% (34/5162) had unknown seafood allergy.
Distribution of seafood allergy in 159 seafood-allergic patients.
The average seafood-allergic patient age was 50.2 (range, 18–81 years) years old and there was no significant difference between the three clinics (VA, 52.7 years [range, 22–81 years]; BT, 47.5 years [range, 22–77 years]; Baylor Clinic, 48.5 years [range, 18–76 years]). The VA patient population made up 45% of the whole patient cohort and had a uniquely high female ratio of 29.6%. Seafood allergy was described slightly more by women (52%; n = 82) than by men (48%; n = 77). Of female seafood-allergic patients, 57.3% (n = 47) reported shellfish allergy, 13.4% (n = 11) had fish allergy, 6.1% (n = 5) reported both fish and shellfish allergy, and 23.2% (n = 19) were unspecified. Of male seafood-allergic patients, 61.0% (n = 47) reported shellfish allergy, 14.3% (n = 11) had fish allergy, 5.2% (n = 4) reported allergy to both fish and shellfish, and 19.5% (n = 15) were unspecified. Allergic rhinitis (51%), asthma (16.6%), and eczema (7.6%) were the most common allergic diseases in the cohort (
A). White and black American ethnicities were dominant (42 and 35%, respectively) with only 10 and 5% of the total number of patients representing Hispanic and Asian ethnic groups, respectively. The remaining patients had no ethnicity recorded (
Figure 2. (A) Number of seafood-allergic, shellfish-allergic, and fish-allergic individuals with coexistent atopic diseases including allergic rhinitis (AR), asthma, eczema, and allergic conjunctivitis (AC). (B) Ethnicity distribution of 159 seafood-allergic individuals. (more ...)
Prevalence of Specific Seafood Allergies
Shellfish allergy (shellfish only and combined shellfish/fish-allergic individuals) was found in 2% of the total clinic population (n = 103/5162). Fish allergy (fish only and combined shellfish/fish-allergic individuals) was noted in 0.6% (n = 31/5162). Shellfish-allergic patients were significantly less likely than fish-allergic patients to report another nonseafood food allergy (p = 0.011).
In patients reporting one or more specific shellfish allergy (n = 69), shrimp (72.5%), crab (34.8%), and lobster (17.4%) were the most frequent allergens. Other reported shellfish included crawfish (14.5%), oyster (8.7%), clam (5.8%), scallop (2.9%), mussel (1.4%), squid (1.4%), and octopus (1.4%; ). Of shellfish-allergic patients, 82.6% were allergic to crustaceans, 7.2% to mollusks, and 10.1% to crustaceans and mollusks. Of 64 crustacean-allergic subjects (including crustacean only and combined crustacean/mollusk-allergic individuals), 24 (37.5%) were allergic to more than one crustacean. Of 12 mollusk-allergic subjects (including mollusk only and combined crustacean/mollusk-allergic individuals), 2 (16.7%) were allergic to more than one mollusk. Twenty-seven shellfish-allergic patients reported reactions to multiple shellfish (39.1%; n = 27/69).
Number of patients reporting specific symptoms to specific shellfish
Of patients who reported one or more fish allergies (n = 21), tuna (28.6%), catfish (23.8%), and salmon (23.8%) were the most frequent allergens. Other reported fish included whitefish (14.3%), cod (9.52%), sardine (9.52%), soulfish (4.76%), trout (4.76%), snapper (4.76%), redfish (4.76%), and caviar (4.76%; ). Seven fish-allergic patients reported allergic reactions to multiple fish (33.3%; n = 7/21).
Number of patients reporting specific symptoms to specific fish
Clinical Symptoms of Seafood Allergy
Skin, respiratory, and GI symptoms were most frequently recorded in allergic reactions (). The most frequent clinical manifestations of the 103 shellfish-allergic patients were skin symptoms (77.7%; n = 80). Respiratory symptoms were the second most common (50.5%; n = 52) and GI symptoms were third. Among 46 crab-, lobster-, and crawfish-allergic patients, 13 (28.3%) developed GI symptoms. Vascular symptoms were less common and were seen in 10–33% of patients with shellfish allergy and both scallop-allergic patients. Eye/nasal symptoms were the least common, occurring in 4% of shrimp- and crab-allergic patients ().
Number of seafood-allergic, shellfish-allergic, and fish-allergic subjects reporting skin, respiratory, gastrointestinal (GI), vascular, eye/nasal, and other symptoms.
Fish-allergic patients reported skin manifestations most frequently (n = 23/24; 95.8%) with respiratory manifestations second most common (14/24 tuna-, salmon-, and whitefish-allergic patients). Sardine-, soulfish-, trout-, and redfish-allergic patients had no other organ involvement other than skin. The single patient with codfish allergy had skin, respiratory, and eye/nasal involvement. The snapper-allergic subject had skin, GI, and eye/nasal symptoms ().
Twenty-four of 50 shrimp-allergic patients (48%) had reactions involving more than one system. Reactions involving more than one organ system were also found in 54% (n = 13/24) crab-allergic, 50% (n = 6/12) lobster-allergic, 40% (n = 4/10) crawfish-allergic, 33.3% (n = 2/6) oyster-allergic, and 75% (n = 3/4) clam-allergic patients. Both scallop-allergic patients had more than one system involved. Each mussel- and octopus-allergic patient had more than one involved organ system. Fish-allergic individuals with tuna, salmon, whitefish, cod, snapper, and caviar allergies had symptoms involving more than one organ system.
The likelihood of having a severe reaction (47%) or anaphylaxis (32%) was not statistically different between shellfish- and fish-allergic subjects. Subjects with severe reactions were 12.9 times more likely to have the reaction in ≤60 minutes compared with those subjects who had nonsevere reactions (p = 0.002).
Chi-square analysis showed a significant difference in respiratory reactions between shellfish- (50%) and fish-allergic individuals (5%; p < 0.05). Logistic regression suggested that shellfish-allergic subjects were six times more likely to experience respiratory symptoms during a reaction than fish-allergic subjects, but this result only approached significance (p =0 .056). Seafood-allergic subjects with respiratory symptoms were 6.5 times more likely to experience that reaction in ≤60 minutes than subjects who did not experience a respiratory reaction (p = 0.021).
Specific IgE Testing
Sixty-eight percent of serum-specific IgE tests to seafood (n = 31) were positive. Of recorded positive tests, only 12 values were recorded (). In this limited number of patients with specific IgE testing, shellfish-allergic patients were more likely to have a positive specific IgE than fish-allergic patients or patients who were allergic to both fish and shellfish, but this finding only approached significance (p = 0.06). Interestingly, 100% of seafood-allergic patients who did not have skin symptoms had a positive specific IgE. Conversely, 58% of patients with skin symptoms had a positive specific IgE. Only 31% of seafood-allergic patients with vascular symptoms had a positive specific IgE.