Anaphylaxis in Outpatients: A 5‐year Retrospective Study on Incidence and Clinical Characteristics at a University Hospital in Wuhan, China

Anaphylaxis is a severe systemic hypersensitivity reaction with acute onset that can potentially be fatal. Currently, the worldwide incidence stands at approximately 46 cases per 100,000 people annually, with rates fluctuating between 0.49 and 328.7 per 100,000 person years1, with considerable variation across age groups and regions. Despite increasing global awareness, research into the prevalence of anaphylaxis within the Chinese population remains sparse. In this retrospective epidemiological study in Wuhan, China, we identified anaphylaxis cases among outpatients using the World Allergy Organization's (WAO) 2020 updated guidelines.2 Acute onset was defined within 6 h post-exposure.3 Potential cases were initially screened via relevant diagnoses (Appendix 1) from the Data Platform Application Portal (DPAP) of Tongji Hospital, Wuhan, China from January 1, 2019, to December 31, 2023. We transformed guidelines into practical descriptions for medical records (Appendix 2). Screening was performed using PyCharm, followed by manual review and data extraction from medical records (Figure 1). The study was approved by the Tongji Hospital IEC (NO. TJ-IRB202401061) with an informed consent waiver. We identified 1026 anaphylaxis patients from a cohort of 6,280,013 outpatients with a female predominance (54.8%) and a median age of 29 years. The crude annual incidence rate was 16.34 per 100,000, which increased to 154.72 after adjusting for age and gender. We observed an increasing trend in incidence over the study period, peaking among adolescents (Figure 1). Identifiable triggers were present in 74.9% (798/1066) of cases, with drugs leading at 40.7% (434/1066). Antibiotics and allergen extracts dominated, accounting for 40.6% (176/434) and 15.9% (69/434). Food followed, contributing to 27.0% (288/1066), showed age-specific features: dairy products were predominant in infants and toddlers (33.3%, 19/57), while seafoods were more common in other age groups (Table 1). Alarmingly, only 10.8% (115/1066) of patients received epinephrine, despite its critical role in anaphylaxis management, with a declining trend in its use over 5 years. Glucocorticoids, antihistamines, calcium gluconate, and bronchodilators were frequently administered. In addition, other medications such as acid-suppressing drugs, water-soluble vitamins, and glucose saline solutions were also widely used in the treatment of anaphylaxis. Notably, 84 patients (8.2%) experienced recurrent episodes, with no fatalities reported. The anaphylaxis incidence rate from our study exceeds some English-speaking regions.4 This may reflect the population and variations in anaphylaxis definitions and diagnostic methods. An annual increment in anaphylaxis incidence was noted, plateauing from 2020 to 2022, suggesting impacts from COVID-19 and resource limitations. Drugs and food were predominant triggers, with age-specific food allergen patterns observed. These data reflect regional, lifestyle, and genetic influences on allergen distribution.5 It is noteworthy that allergen extracts were the second highest drug-related trigger for anaphylaxis, with 55.1% (38/69) caused by crude allergen extracts (Appendix 3). This could be due to the fact that more than 3000 outpatients receive subcutaneous immunotherapy treatments at our center annually, and anaphylaxis induced by subcutaneous immunotherapy is not uncommon. Alarmingly, epinephrine use for anaphylaxis treatment has declined to a mere 10.8%, lower than other Chinese studies (14.2%–25%).6 This reflects a notable lack of awareness and understanding of anaphylaxis among our medical practitioners. In clinical settings, there is often hesitation to administer epinephrine promptly to patients experiencing anaphylaxis without shock. This reluctance stems from concerns about potential adverse reactions, including the induction of malignant arrhythmias. As a result, the use of epinephrine is largely confined to critical scenarios. This study's limitations include potential recall bias and variability in medical record documentation. Besides, serum tryptase detection kits have not yet received marketing approval in China, which precludes the possibility of using serum tryptase to further verify the diagnosis of anaphylaxis in patients initially identified by our physicians. Also, unmeasured confounding factors cannot be eliminated, such as the population consists of patients seeking medical treatment. It is noteworthy that while the DPAP system is restricted to internal hospital use and is not transferable, the extensive data set of 75 million medical records from over 16 million patients mitigates some biases. RZ and PD conceived and designed the project. LL and HC set up the data screening procedure and generated the figures. LL, NH, WL, YY, and DM manually screened and collected the patients' information. LL wrote the first draft of the manuscript, RZ and PD revised the raw manuscript. All authors critically revised the manuscript and approved the submitted manuscript. We would like to thank the Tongji Hospital affiliated with Huazhong University of Science and Technology for providing the data platform used in this study. This study did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Thus, there are no funding information to report. There are no financial or other issues that might lead to conflict of interest. None, without accompanying symptoms, denying symptoms, not seen, not reported by the patient, not experienced by the patient, if present, if there is any, occasionally present, intermittent. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.