Fig. 1

The illustration of the modified SEIR model. The model categorized the whole population into five subpopulations, susceptible (S), exposed and infected (not yet infectious) (E), infectious (I), infectious and isolated (IS) and removed (R). The IS group was further divided into two sub-populations according to the type of quarantine: those who were centralized quarantined (ISC) or home-based quarantined (ISH). E was further designated into a subpopulation K indicating key population to the XFD market, a subpopulation C indicating close contacts of confirmed cases, a subpopulation N representing the infections discovered by nucleic acid testing and a subpopulation O representing the infections identified by other methods