Although elevated, the median antibody index of positive samples in the bacterial infection group was still significantly lower than the one of the COVID-19 group for all assays (Vircell-IgM/A: 12.7 versus 21.7; Vircell-IgG: 10.5 versus 33.8; Euroimmun-IgA: 1.4 versus 3.2; Euroimmun-IgG: 1.6 versus 4.1). This evidence concerns the gene CD40LG and bacterial infectious disease.