Characteristics of Anaphylactic Reactions: A Prospective Observational Study in Japan

Background: Anaphylaxis is a systemic, life-threating, allergic reaction in which the clinical features may vary in different populations or due to the allergic triggers. Moreover, the timing and characteristics of biphasic anaphylactic reactions remain unclear. Objectives: The purpose of this study was to investigate the clinical characteristics of anaphylaxis cases assessed and treated in Japanese hospitals. Methods: This was a prospective observational study of anaphylactic reactions treated in the Emergency Department (ED) of two medical centers from June 2016 to May 2019. All patients diagnosed with anaphylaxis were enrolled in this study. Data collected included patient demographics, symptoms and signs, treatment, clinical course, and suspected triggers. Descriptive statistics and univariate methods were used in the analyses. Results: We enrolled 302 patients. The median age was 32 years (interquartile range 13–37) and the sample included 182 (60.3%) women. Of the 302 patients, 179 (59.3%) had a history of allergic reactions. The dermatologic, respiratory, gastrointestinal, and cardiac systems were involved in 297 (98.3%), 248 (82.1%), 150 (49.7%), and 55 (18.2%), respectively. Nineteen patients (6.3%) experienced biphasic anaphylactic reactions. Epinephrine use was associated with a lower incidence of biphasic anaphylactic reaction (odds ratio 0.3, 95% confidence interval 0.1–0.9). Time to recurrence of symptoms ranged from 2 to 48 h (median: 10 h). Conclusions: In this prospective ED study, foods were the most common triggers of anaphylaxis, and epinephrine administration was associated with a decreased occurrence of biphasic anaphylactic reactions. Over half of patients experiencing biphasic anaphylactic reactions developed symptoms more than 10 h after presentation.