Since infection is caused by pathogens (such as bacteria and viruses) it can take some time before the microbes multiply enough to trigger symptoms of illness.
This means an infected person may unwittingly be spreading the disease during this incubation period.
Infectious agents can be spread in a variety of ways, including:
- Airborne - coughs or sneezes release airborne pathogens, which are then inhaled by others
- Contaminated objects or food - the pathogens in a person's faeces may be spread to food or other objects, if their hands are dirty
- Skin-to-skin contact - the transfer of some pathogens can occur through touch, or by sharing personal items, clothing or objects
- Contact with body fluids - pathogens in saliva, urine, faeces or blood can be passed to another person's body via cuts or abrasions, or through the mucus membranes of the mouth and eyes.