Typhoid fever

Causes of typhoid fever

Typhoid fever is caused by a type of bacteria called Salmonella typhi.

This is not the same type of bacteria that can cause salmonella food poisoning, but the two are related.

How the infection spreads

When someone with the infection has a bowel movement, they may pass faeces that contain the Salmonella typhi bacteria. If they do not wash their hands properly after going to toilet, they can contaminate any food they touch. If this is eaten by another person, they will also become infected.

Less commonly, the Salmonella typhi bacteria can spread after a person urinates. Again, if an infected person handles food without washing their hands properly after urinating, they can spread the infection on to someone else who eats the contaminated food.

In parts of the world that have poor levels of sanitation, infected human waste can contaminate the water supply. People who drink contaminated water or eat food that has been washed in contaminated water can contract typhoid fever.

Other ways that typhoid fever can be contracted include:

  • using a toilet that has been contaminated with bacteria and touching your mouth before washing your hands
  • eating shellfish or similar seafood that from a water source that has been contaminated by infected faeces or urine 
  • having oral or anal sex with a person who is a carrier of Salmonella typhi bacteria (see below)


If typhoid fever is not treated, an estimated 1 in 20 people who survive the infection will become carriers of the condition. This means that the Salmonella typhi bacteria continue to live in their bladder, and they can still spread typhoid fever in their faeces or urine. However, carriers of typhoid fever do not have any symptoms themselves.

The effects of typhoid fever

After a person eats or drinks food or liquid that is contaminated with the Salmonella typhi bacteria, the bacteria will move down into their digestive system. The bacteria will quickly multiply, triggering the initial symptoms such as a high temperature, abdominal pain and constipation or diarrhoea.

If the person is not treated, the bacteria will spread into the bloodstream, intestines, liver and bone marrow. The spread of bacteria out of the bowel causes the symptoms to get worse during the second and third weeks of the infection.

If the organs and tissue become damaged, it can cause complications, such as internal bleeding or a section of the bowel splitting open.


Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and others are good for you.

Bone marrow
Bone marrow is the soft, spongy tissue in the centre of bones that produces blood cells.

Diarrhoea is the passing of frequent watery stools.

Stool (also known as faeces) is the solid waste matter that is passed from the body as a bowel movement.

Last updated: 31 January 2012

Continue to next section: Diagnosing typhoid fever