The source of infection is a very important factor in the epidemiology of infectious diseases, which requires three basic conditions in the process of epidemiology, including the source of infection, the means of transmission and the susceptibility of the population. The source of infection refers to people or animals that have pathogens in their bodies that survive, reproduce, and are able to excrete the pathogens out of their bodies. The source of infection includes patients, latently infected people, carriers of the virus, and infected animals. The route of transmission refers to the way in which the pathogen leaves the source of infection and reaches another susceptible person, and there are multiple routes of transmission for the same infectious disease. A susceptible person is a person who lacks specific immunity to an infectious disease and is susceptible to the pathogen. In the case of the currently prevalent New Coronavirus (NCV), for example, the source of infection includes patients with NCV as well as people with latent infections who carry the virus.