The portal of entry is the path that will be followed by the virus, bacteria, or germ in order to infect a new host. If this occurs, this means that more and more people will get infected until it can become an outbreak. Take note that there are different portals of entry such as broken skin, the respiratory tract and even through the tubes.
There are some people who become infected when they are in hospital. They get infectious agents through their catheters. This can always be stopped if people would always be more careful and will also be more hygienic.
In the circular chain of infection, pathogens must be able to leave their reservoir and be transmitted to a susceptible host through a portal of entry, such as broken skin.