Moreover, we have found that SARS-CoV-2 could be detected in saliva by collecting saliva from COVID-19 patients and dry mouth as well as amblygeustia could be considered as initial symptoms of SARS-CoV-2 infection [12], which means oral tissues are most likely an important entry route for SARS-CoV-2, and the susceptibility of oral epithelial cells to SARS-CoV-2 may also be related to the expression levels of ACE2 and TMPRSS2. This evidence concerns the gene TMPRSS2 and COVID-19.