There are three basic conditions for the epidemiologic process of infectious diseases, including the source of infection, the means of transmission and the susceptible population.
1. Source of infection: It refers to people or animals that have pathogens in their bodies that survive, reproduce and can expel pathogens from their bodies. Including patients, hidden infected, pathogen carriers and infected animals, etc., of which the patient is a very important source of most infectious diseases.
2. Transmission: pathogens leave the source of infection to reach another susceptible pathway is called transmission. The main ways are respiratory transmission, gastrointestinal transmission, contact transmission, blood transmission and medical transmission.
3. Population susceptibility: the lack of specific immunity to a particular infectious disease is called susceptible, susceptible to a particular proportion of the population to determine the susceptibility of the population.
The epidemic process of infectious diseases requires the above three basic conditions, these three links must exist at the same time, if you cut off any of the links, the epidemic will be declared terminated.