Divided into Invasion and colonization and Exit of pathogen.
a. Invasion and colonization
colonization is the presence of bacteria on a body surface (like on the skin, mouth, intestines or airway) without causing disease in the person. Infection is the invasion of a host organism’s bodily tissues by disease-causing organisms.
b. Exit of the pathogen
Portal of exit is the path by which a pathogen leaves its host. The portal of exit usually corresponds to the site where the pathogen is localized.