Sample and Setting
This study was conducted in six tertiary medical institutions within Metro Manila, Philippines which cater the medical needs of COVID-19 patients. Patients were eligible if they were at least 18 years old; Filipino citizen; hospitalized in the selected hospitals in Metro Manila, regardless of clinical symptomatology and case severity, from March 2020 to January 2022; have real time polymerase chain reaction (RT-PCR) result test via nasopharyngeal and/or oropharyngeal swabs in an accredited laboratory; and, have blood typing result. Medical records with incomplete data were excluded.
Sample size computation (priori ) for binary logistic regression analysis was conducted using GPower version 3.1.9.4. According to Latz et al.,6 the odds ratio for COVID-19 infection was 1·37 for blood type AB, with a null probability of 19·80% and R2-value of 0·005. With these parameters, a minimum power of 80%, and a significance level of 5% (two-tailed), a minimum sample size of 401 respondents was necessary. The sample size was inflated to accommodate 20% attrition; hence, the final sample size was at least 502 respondents.