Causes

Typhoid fever is caused by dangerous bacteria called Salmonella typhi. Salmonella typhi is related to the bacteria that cause salmonellosis, another serious intestinal infection, but they aren't the same.

Fecal-oral transmission route

Most people in developed countries pick up typhoid bacteria while they're traveling. Once they have been infected, they can spread it to others through the fecal-oral route.

This means that Salmonella typhi is passed in the feces and sometimes in the urine of infected people. If you eat food that has been handled by someone who has typhoid fever and who hasn't washed carefully after using the toilet, you can become infected.

In developing countries, where typhoid fever is established, most people become infected by drinking contaminated water. The bacteria may also spread through contaminated food and through direct contact with someone who is infected.

Typhoid carriers

Even after antibiotic treatment, a small number of people who recover from typhoid fever continue to harbor the bacteria. These people, known as chronic carriers, no longer have signs or symptoms of the disease themselves. However, they still shed the bacteria in their feces and are capable of infecting others.