The chain of infection refers to how pathogenic microorganisms are transmitted. All "links in the chain" must be present in order for infection to occur. The sequence is as follows:
1. There must be a causitive agent or pathogen.
2. There must be a source or resorvoir, example, a carrier.
3. There must be a portal of exit. The microbe must leave the body by some means.
4. There must be a mode of transmission. example, sneezing.
5. There must be a portal of entry. example, respiratory tract.
6. There must be a susceptible host. If someone is not susceptible to disease, the disease can't be transmitted.
A goal of all health care workers is to try and break the chain of infection by utilizing preventative measures. Commonly, health care workers are guilty of spreading infections due to incorrect and sloppy practices.