Demographics of fish allergic participants
Sixty-seven and forty-six subjects fulfilling the inclusion criteria
were recruited from the pediatric allergy clinics in HK and the
Sagamihara National Hospital in Japan respectively (Table 1,
Supplementary Tables E1, E2). The median (range) age of fish allergic
subjects at evaluation was 6 (1-16) years and 10 (5-18) years for these
two populations, respectively. The most common clinical features shared
among the two populations were itchy mouth/throat (61.1%, 69/113) and
urticaria (51.3%, 58/113) while subjects from HK also commonly
displayed angioedema (59.7%, 40/67) upon fish ingestion (Supplementary
Tables E1, E2). The two populations did not differ in terms of the
symptom severity as reflected from oFASS (p = 0.5251). SPT to fish mix
extract was only available for subjects recruited in HK with median
(range) SPT wheal size of 5 (0-11) mm, and 48 subjects (84.2%) had
positive SPT (cutoff at 3mm). The sIgE results for cod, tuna, salmon and
grass carp are summarized in Table 1 and detailed in supplementary
Tables E1 and E2. No difference was detected in sIgE levels to these
fish species between the two populations, except for grass carp that HK
subjects had significantly higher sIgE level comparing to Japanese
subjects (Mann-Whitney test, p = 0.0020). Of note, 65/67 (97.0%) and
34/37 (91.8%) subjects from HK and Japan had positive sIgE to salmon
(cutoff at 0.35kUA/L), of whom 72.3% and 70.6% had high sIgE level and
above class III-VI, respectively. As for grass carp, 63/67 (95.5%) and
25/30 (83.3%) subjects from HK and Japan had positive sIgE, of whom
87.3% and 56.0% had high sIgE level and above class III-VI,
respectively. An overall positive correlation between sIgE levels to
salmon and grass carp was observed for both populations, by which a
stronger correlation was found among the Japanese subjects (r = 0.69, p
= 0.0002) than HK subjects (r = 0.33, p = 0.0061) based on Fisher r-to-z
transformation (z = 2.01, p = 0.04). Sera of Japanese subjects yielded
high sIgE response to salmon with an average grass carp/salmon sIgE
ratio of 0.70 (0.02-1.93) while sera of HK subjects yielded higher sIgE
response to grass carp with average ratio of 3.39 (0.02-20.8)
(Supplementary Figure 1). Pairwise comparison between grass carp- and
salmon-specific IgE levels also showed statistically higher grass
carp-specific IgE level among HK subjects but statistically higher
salmon-specific IgE level among Japanese subjects (Wilcoxon
matched-pairs signed rank test, p = 0.0008 and 0.0315 respectively).