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.