Causes of typhoid fever 

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

This isn't the same bacteria that cause salmonella food poisoning, but the two are related.

How the infection spreads

The Salmonella typhi bacteria will be in the stools (poo) of an infected person after they've been to the toilet. If they don't wash their hands properly afterwards, they can contaminate any food they touch. Anyone else who eats this food 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 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
  • eating raw vegetables that have been fertilised with human waste
  • contaminated milk products
  • having oral or anal sex with a person who's a carrier of Salmonella typhi bacteria


Up to 1 in 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 eating food or drinking fluid contaminated with the Salmonella typhi bacteria, the bacteria will move down into the digestive system, where they will quickly multiply. This triggers a high temperature, stomach pain and constipation or diarrhoea.

Left untreated, the bacteria can get into the bloodstream and spread to other areas of the body. This can cause the symptoms of typhoid fever to get worse during the weeks after infection.

If organs and tissues 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 complications of typhoid fever.

Page last reviewed: 06/07/2015

Next review due: 06/07/2017