LAUSR

To the Editor, Hen's egg (HE) is consumed worldwide and is one of the most frequent causes of food allergy.1,2 In Japan, HE is the most commonly consumed avian egg, followed by quail's egg (QE). Quails (Coturnix japonica) belong to the same Galliformes Phasianidae family as the chicken (Gallus gallus domesticus); therefore, crossreactivity may occur between HE and QE. Consequently, HEallergic patients are generally advised to avoid QE consumption. However, there are only one report on serological crossreactivity between HE and QE,3 and two reports on clinical crossreactivity.4,5 Therefore, whether all HEallergic patients need to avoid QE consumption remains unclear. This study aimed to evaluate the clinical crossreactivity between HE and QE by performing oral food challenge (OFC) tests. We conducted a prospective study to determine whether HEallergic patients show clinical crossreactivity to QE. We performed QEOFC in patients with HE allergy between January 2018 and October 2019. HE allergy was diagnosed through OFCs, which were performed stepwise, starting from a lowdose HEOFC (containing 1/25 of a heated HE). Patients with negative results proceeded to a mediumdose HEOFC (containing 1/8 of a heated HE). Patients with a positive lowdose or mediumdose HEOFC were included in this study. Patients with missing clinical data were excluded. QEOFC was performed using one heated QE. Serum levels of total immunoglobulin E (IgE) and specific IgE to HE white (HEwsIgE), HE ovomucoid (OVMsIgE), and QE white (QEwsIgE) (ImmunoCAPTM; Thermo Fisher Scientific/Phadia) were measured within 4 months of conducting QEOFC. A skin prick test (SPT) was performed during the QEOFC. The SPT procedure is described in Appendix S1. This study was approved by the ethics committee of Sagamihara National Hospital (approval number: 2017021) and was registered at the University Hospital Medical Information Network Clinical Trials Registry (no: UMIN000034820). Written informed consent was obtained from the guardians of all patients. Among 870 patients who underwent HEOFC, 183 failed the lowdose or mediumdose HEOFC, 22 of whom underwent a QEOFC. The threshold dose of HE was significantly higher in patients who received QEOFC than in those who did not (Table S1). Two patients were excluded because of missing clinical data, and the remaining 20 were enrolled (Figure 1). The median patient age was 2.9 (range, 1.0– 16.4) years, and 10 (50%) patients had a history of anaphylaxis to HE. The median HEwsIgE, OVMsIgE, and QEwsIgE levels were 9.95 (2.67– 365), 8.66 (<0.10– 191), and 4.15 (0.73– >100) kUA/L, respectively (Table 1). There was a correlation between HEwsIgE and QEwsIgE levels (Figure S1). SPT was performed in 13 patients, and 12 (92%) were found to be sensitized to QE. The median SPT wheal diameters for HEw and QEw were 15 (3– 32) and 12 (0– 25) mm, respectively. Among the 20 patients, four reacted to the lowdose HEOFC (threshold dose, ≤1/25 of a heated HE), and 16 passed the lowdose but reacted to the mediumdose HEOFC (threshold dose, >1/25– 1/8 of a heated HE). Of the 20 patients, nine (45%) failed the QEOFC. The median interval between QEOFC and HEOFC was 2.8 months. The rate of positive QEOFC results was significantly higher in patients with a threshold dose of ≤1/25 of a heated HE than in those with a threshold dose of >1/25– 1/8 of a heated HE (100% [4/4] vs. 31% [5/16], p =.026; Figure 2). Patients’ symptoms, severity, and treatment during the QEOFC are described in Table S2. Three patients presented with symptoms in multiple organs; however, their symptoms improved after treatment with antihistamines, steroids, and/or inhalation of β2 stimulants. The HEwsIgE, OVMsIgE, and QEwsIgE levels were significantly higher in patients with a positive QEOFC result than in those with a negative QEOFC result. There was no significant difference in the SPT wheal diameter to HEw and QEw between patients who reacted to QEOFC and those who did not (Table 1). In this study, some HEallergic patients showed clinical crossreactivity to QE, especially those with a low threshold of HE. In a previous report, approximately 70% of HEallergic children had positive SPT results to raw QEw.6 In another report, 33% (4/12) of HEallergic children had positive SPT results to boiled QEw. Four of the remaining 8 patients with negative SPT results underwent OFC using boiled QEw, and one reacted.5 In our study, 92% of HEallergic patients had positive SPT results to raw QEw; all participants underwent QEOFC, and 45% reacted. The mean weight of HE and QE is 58 and 11.3 g, respectively.7 Because the ratio of egg white to egg yolk mass in HE is almost equivalent to that in QE,7,8 and the percentage of protein in HEw is also equivalent to that in QEw,7 the amount of protein in the egg