Most infections are caused by either bacteria or viruses, which can enter the body via a number of routes, including:
- Exposure to infected droplets when an infected person sneezes or coughs, either via inhalation of the droplets while they’re in the air, or by coming into contact with them on surfaces such as tables, crockery, or toys
- Broken skin (for example a cut, scratch or graze)
- Consumption of contaminated food or water
- Contact with the faeces, vomit or bodily fluids of an infected person (this includes sexual intercourse and the sharing of hypodermic needles)
- Bites from infected animals.
The immune system’s primary role is to ward off pathogens, so its health and function have implications for the prevention of and recovery from infection, and susceptibility to infection may be an indication of immune dysfunction.
In otherwise healthy people, frequent or persistent minor infections (such as colds) may be an indication that immune system function is sub-optimal.
Amongst other causes, increased susceptibility to infection may be due to disease (including HIV/AIDS, diabetes and some forms of cancer), malnutrition, or may occur as a side effect of some prescribed medicines including corticosteroids and chemotherapy.