Peritonitis is inflammation of the peritoneum, the thin layer of tissue that lines the inside of the abdomen (tummy).

It is caused by an infection, which can rapidly spread around the body. Peritonitis requires immediate treatment and is a medical emergency. Signs of peritonitis often develop quickly and include:

• sudden abdominal pain that becomes more severe
• feeling sick (nausea)
• a lack of appetite
• a high temperature (fever) of 38C (100.4F) or above
• not passing any urine or passing less than normal

Read more about the symptoms of peritonitis.

When to get medical help

Sudden abdominal pain that gradually gets worse is usually a sign of a potentially serious infection or illness.

If you have this type of pain, contact your GP immediately. If this isn't possible, call NHS 111 or your local out-of-hours service.

Why peritonitis happens

Peritonitis is caused by a bacterial or fungal infection that either develops directly in the peritoneum or spreads from another part of the body.

Most cases of peritonitis are the result of infection or injury to another part of the body, such as:

• a split stomach ulcer
• a burst appendix
• digestive disorders, such as Crohn's disease or diverticulitis

An infection that develops within the peritoneum isn't common and can be caused by:

• cirrhosis – scarring of the liver caused by long-term liver damage
• peritoneal dialysis – a widely used treatment for people with kidney failure

Read more about the causes of peritonitis.

How peritonitis is treated

Peritonitis needs to be diagnosed and treated quickly to prevent possibly fatal complications developing, so you will usually be admitted to hospital for tests and treatment.

The underlying infection will be treated with injections of antibiotics or antifungal medication, depending on the cause.

In some cases, surgery may be required to repair the peritoneum or treat the underlying cause of the infection.

Read more about diagnosing peritonitis and treating peritonitis.

Complications

Peritonitis can be fatal if the infection spreads through the bloodstream to the major organs (septic shock).

It's estimated about 1 in every 10 people with peritonitis caused by bowel perforation (a hole that develops in the bowel wall) will die, although this can vary considerably depending on what caused the condition, your age, and your general health.

Deaths are less common for peritonitis related to cirrhosis or kidney dialysis, but it's still a serious condition.

Read more about the possible complications of peritonitis.