Collection of anonymised patient data
Anonymised patient data from the Hospital Authority was collected by the Information Technology and Health Informatics Division, Hospital Authority Head Office. Informed consent was waived (because all data were anonymous and collected retrospectively) and data extraction was approved by the institutional review board of the University of Hong Kong and Hospital Authority Hong Kong West Cluster. Hong Kong is a unique entity where the Hospital Authority is the sole publicly funded healthcare system for the entire territory. It possesses facilities in seven regions (Hong Kong East, Hong Kong West, Kowloon Central, Kowloon East, Kowloon West, New Territories East, and New Territories West), comprising 43 hospitals, 49 specialist outpatient clinics, and 73 general outpatient clinics; it provides approximately 90% of all in-patient services.19 All clinical services utilise a unified ‘Electronic Patient Records’ system, providing medical records for over 7.3 million individuals. This system allows complete and uniform drug allergy data to be gathered and analysed. A snapshot of cross-sectional data from all available patient records was retrieved as of 23rd July, 2021. Physician-reported drug allergy, age at the time of reported drug allergy and names of reported culprits were collected. Incidence of newly reported drug allergy, as well as all cases of anaphylaxis and Stevens-Johnson syndrome from 1st January, 2016 to 31st December, 2020 were reviewed. Drugs were categorised according to the British National Formulary Drug Classes, except for non-steroidal anti-inflammatory drugs (NSAIDs), which were separated into its own category.20 Drugs which were entered as ‘free text’ into the electronic system were checked and converted back to structured drug items when possible. Those ‘free text’ reported drug allergy which could not converted or were incomplete were excluded from analysis. Drugs which did not fit into any drug classes were categorised as ‘Others’ and listed in Supplementary Text 1.