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 stools (faeces) that contain the Salmonella typhi bacteria. If they do not wash their hands properly after going to the toilet, they can contaminate any food they touch. If this is eaten by another person, they may also become infected.

Less commonly, the Salmonella typhi bacteria can be passed out in an infected person's urine. Again, if an infected person handles food without washing their hands properly after urinating, they can spread the infection to someone else who eats the contaminated food.

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

Other ways typhoid fever can be contracted include:

• using a toilet contaminated with bacteria and touching your mouth before washing your hands
• eating seafood from a water source contaminated by infected faeces or urine 
• having oral or anal sex with a person who is a carrier of Salmonella typhi bacteria

Carriers

Up to 1 in every 20 people who survive typhoid fever without being treated will become carriers of the infection. This means the Salmonella typhi bacteria continue to live in the carrier's body and can be spread as normal in faeces or urine, but the carrier doesn't have any noticeable symptoms of the condition.

How the bacteria affect the body

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

If the person is not treated, the bacteria can get into the bloodstream, which means they can spread to other areas of the body. The spread of bacteria out of the digestive system can cause the symptoms of typhoid fever to get worse during the weeks after infection.

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

Read more about the symptoms of typhoid fever and the complications of typhoid fever.

Bacteria
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
Diarrhoea is the passing of frequent watery stools.

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