Statistical analysis

Statistical analysis was done using the SPSS statistical package (IBM, 2015, Armonk, New York, USA). We adjusted the prevalence for test sensitivity at 90% and specificity at 99%, following the manufacturer's estimates. The adjusted prevalence of IgG antibodies to SARS-CoV-2 in blood donors was reported as percentages with 95% confidence intervals (CI). Quantitative variables were calculated as mean ± standard deviation and a P < 0.05 was considered statistically significant. Social and demographic variables of blood donors were compared between reactive and nonreactive groups. Qualitative variables and quantitative variables were analyzed using the Chi-square test and paired Student's t-test, respectively.