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Peritonitis is inflammation of the peritoneum, the thin layer of tissue that lines the inside of the abdomen and surrounds and supports organs, such as the stomach and liver.

It's caused by a bacterial or fungal infection. An infection of the peritoneum can rapidly spread into the blood and then on to the body’s organs.

Symptoms of peritonitis often come on quickly and include:

  • severe abdominal pain
  • a high temperature (fever) of 38C (100.4F) or above
  • chills

Due to a high risk of serious complications developing, peritonitis is regarded as a medical emergency and requires immediate treatment.

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 is not possible, call NHS Direct Wales on 0845 4647 or your local out-of-hours service.

Causes of peritonitis

The most common cause of peritonitis is an infection that develops directly inside the peritoneum. Doctors refer to this as primary peritonitis.

The two major risk factors for primary peritonitis are:

It is estimated that 20% of people with cirrhosis who have a build-up of fluid inside their abdomen will also develop peritonitis at some point.

Following advancements in treatment, peritonitis associated with dialysis is less common than it used to be. It's estimated that most people being treated with peritoneal dialysis will experience one episode of peritonitis every two years.

A less common cause of peritonitis is an infection or injury in another part of the body that causes bacteria or fungi to infect the peritoneum. Doctors refer to this as secondary peritonitis.

If part of the digestive system breaks open as a result of an injury or an infection, for example when the appendix bursts due to appendicitis, bacteria can be released inside the peritoneum. 

Treatment for peritonitis

Peritonitis is a serious condition that needs to be diagnosed and treated quickly to prevent possibly fatal complications developing. Therefore, it's regarded as a medical emergency and treatment for peritonitis will usually involve being admitted to hospital.

The underlying infection will be treated with injections of antibiotics or antifungal medication, depending on the cause of the infection. In some cases, surgery may be required to repair damage to the peritoneum or to treat the underlying cause of the infection.

However, due to the often aggressive nature of peritonitis, death can occur despite the best efforts of medical staff.


The outlook for peritonitis varies widely depending on its cause. Peritonitis associated with cirrhosis has the worst outlook, with the risk of death being as high as 50%, whereas it’s estimated that 10% of people will die from secondary peritonitis.

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The initial symptoms of peritonitis are a lack of appetite and feeling sick.

These are quickly followed by abdominal pain, which usually begins as a dull ache before progressing to a steady, severe pain.

Other symptoms of peritonitis include:

  • vomiting
  • chills
  • a high temperature (fever) of 38C (100.4F) or above
  • rapid heartbeat
  • feeling thirsty
  • not passing any urine or passing less than normal
  • diarrhoea
  • swelling of the abdomen
  • yellowing of your skin and the whites of your eyes (jaundice)

If you are being treated with peritoneal dialysis because you have kidney failure, the fluid that is passed into your collection bag will probably be cloudier than usual and it may contain white flecks or clumps.

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 experience this type of pain, contact your GP immediately. If this is not possible, call NHS Direct Wales on 0845 4647 or your local out-of-hours service.

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The most common cause of peritonitis is cirrhosis, which is where the liver becomes scarred.

Cirrhosis can have a range of causes, the most common of which are:

  • liver damage caused by persistent alcohol misuse
  • liver damage caused by the viral infection hepatitis C
  • being obese (fat molecules can damage the liver’s tissue in much the same way as alcohol)

In some parts of the UK, obesity has overtaken alcohol as the most common cause of cirrhosis.

Cirrhosis can lead to a build-up of fluid inside the abdomen. This provides an opportunity for bacteria and, less commonly, fungi to trigger an infection. The medical term for a build-up of fluid inside your abdomen is ascites.

Ascites affects around half of people with cirrhosis, usually many years after cirrhosis was originally diagnosed. About 20% of people with cirrhosis who develop ascites will be affected by peritonitis.

Peritoneal dialysis

People with kidney failure who are having a treatment known as peritoneal dialysis are at risk of developing peritonitis. Dialysis is a medical treatment that replicates the main functions of the kidneys and removes waste products from the body.

Peritoneal dialysis involves using the peritoneum to replicate the main function of the kidneys, which is to filter waste products out of the blood. A small tube, called a catheter, is implanted into the blood vessels of the peritoneum and waste products are removed through the catheter.

The major disadvantage of peritoneal dialysis is that the equipment can become contaminated by bacteria or fungi, which can lead to an infection of the peritoneum. Therefore, as a precaution, people who are having peritoneal dialysis are often given antibiotics.

Factors that can increase the risk of peritonitis in people who having peritoneal dialysis include:

  • being overweight or obese
  • being female
  • having another long-term health condition, such as type 2 diabetes or high blood pressure
  • smoking
  • being elderly (the older you are, the higher your risk of developing peritonitis)

It is unclear why some of these risk factors increase the likelihood of developing peritonitis.

Other causes

Peritonitis can be caused when an injury or infection inside the abdomen allows the bacteria or fungi into the peritoneum. This is called secondary peritonitis. Common causes of secondary peritonitis include:

Both Crohn’s disease and diverticulitis can cause the colon to become inflamed. If the inflammation is particularly severe, the colon can split and leak the contents of the bowel onto the peritoneum, contaminating it with bacteria.

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Diagnosing peritonitis will involve checking whether the peritoneum is inflamed and, if it is, determining the cause.

Physical examination

Your GP will ask you about your symptoms and your recent medical history, and will carry out a detailed physical examination.

If you have peritonitis, parts of the body such as the chest wall often become very tender to the touch. A physical examination will help rule out other conditions that can cause similar symptoms, such as a hernia.

The risk of complications from peritonitis is high. Therefore, if your GP suspects that you have it, they will probably arrange for you to be admitted to hospital immediately for further testing.

Further testing

Further tests for peritonitis may include blood tests and urine tests, to check for infection.

Doctors may also recommend:

These types of scans can often detect whether there is internal damage inside your abdomen, such as a burst appendix, a ruptured stomach ulcer or extensive inflammation of the colon.

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If you're diagnosed with peritonitis, you will be admitted to hospital where you will be carefully monitored due to the risk of serious complications, such as blood poisoning.

Antibiotics or antifungal medication

The initial treatment for peritonitis involves injections of antibiotics or antifungal medication. The course will usually last 10 to 14 days.

If your peritonitis was caused by peritoneal dialysis, antibiotics may be injected directly into the tissue of the peritoneum. Research has shown that this is more effective than injecting antibiotics in a vein.

You will also need to use an alternative method of dialysis, such as haemodialysis (where the blood is passed through a machine that has a series of filters) until the peritonitis has been successfully treated.


If part of the tissue of the peritoneum has been seriously damaged by infection, it may need to be surgically removed.

Some people develop abscesses (pus-filled swellings) in their peritoneum, which will need to be drained. This can be done under a local anaesthetic. An ultrasound scanner will be used to guide a needle to the abscess to remove the pus. Read more about treating abscesses.

The cause of peritonitis may also need to be surgically treated. For example, if a burst appendix caused your peritonitis, your appendix will need to be removed. Read more about treating appendicitis.

If peritonitis was caused by liver disease that led to a build-up of fluid inside the abdomen, the fluid will need to be drained out of the abdomen. Read more about treating cirrhosis.

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Blood poisoning (sepsis) is the most serious complication of peritonitis. It can occur if the peritoneum becomes infected and the infection spreads into the blood and then to other organs.

If sepsis is not treated, it can progress to a more serious phase known as severe sepsis. Severe sepsis occurs when one or more organs are damaged by the infection, or when there is a significant loss of blood supply to tissues and organs.

The symptoms of sepsis usually develop quickly and include:

  • a fever or high temperature over 38C (100.4F)
  • chills
  • a fast heartbeat
  • fast breathing

Treatment for sepsis involves antibiotic injections.

Septic shock

Septic shock is a type of sepsis that causes a massive drop in blood pressure. This leads to symptoms of shock, such as:

  • cold skin
  • increased heartbeat

Sepsis can interfere with many of the body’s vital processes, including blood pressure, breathing and organ function, and can result in death.

Treatment usually requires admission to an intensive care unit (ICU) where the functions of the body’s organs will be supported while the infection is treated.

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