Study Outcomes and Data Measures
The exposure variable was the ABO blood type, which was based on blood typing result available in the medical records, and the comparison/control group was the absence of specific blood type antigen (e.g., Type A vs. Non-A Blood Type; Type B vs. Non-B Blood Type; Type AB vs. Non-AB Blood Type; Type O vs. Non-O Blood Type). The primary outcome was COVID-19 infection and severity which were based on the RT-PCR result and the national and international interim guidelines on COVID-19, respectively. The secondary outcomes were ICU admission, intubation, and mortality.
The data were recorded in an abstraction form which included demographic data, medical and clinical data, and the COVID-19 infection data. Demographic data included birthdate, sex, marital status, educational attainment, and occupation. The medical and clinical data involved the chief complaint; admission and final diagnoses, admission date, unit of admission, comorbidities, medications, anthropometric measurements, blood chemistry and inflammatory markers, medical managements, blood type, ICU admission and discharge, intubation and/or extubation, duration of hospital and ICU stays, and mortality. Finally, COVID-19 infection data included the date of RT-PCR specimen collection and result, the test result, clinical category, clinical symptomatology, and results of chest radiographic imaging, if any.