Complications caused by typhoid fever usually only occur in people who haven't been treated with appropriate antibiotics or who weren't treated straight away.
In such cases, about 1 in 10 people experience complications, which usually develop during the third week of infection.
The 2 most common complications in untreated typhoid fever are:
Most internal bleeding that occurs in typhoid fever isn't life threatening, but it can make you feel very unwell.
A blood transfusion may be required to replace lost blood, and surgery can be used to repair the site of the bleeding.
Perforation is potentially a very serious complication. This is because bacteria that live in your digestive system can move into your stomach and infect the lining of your abdomen (the peritoneum). This is known as peritonitis.
Peritonitis is a medical emergency as the tissue of the peritoneum is usually sterile (germ-free).
Unlike other parts of the body, such as the skin, the peritoneum doesn't have an inbuilt defence mechanism for fighting infection.
In peritonitis, the infection can rapidly spread into the blood (sepsis) before spreading to other organs.
This carries the risk of multiple organ failure. If it isn't treated properly, it may result in death.
The most common symptom of peritonitis is sudden abdominal pain that gets progressively worse.
If you have peritonitis, you'll be admitted to hospital, where you'll be treated with antibiotic injections.
Surgery will then be used to seal the hole in your intestinal wall.
Read more about treating peritonitis.