Peritonitis occurs when the peritoneum becomes infected with bacteria or fungi.

The peritoneum is the thin layer of tissue lining the inside of the abdomen (tummy).

The infection can either develop directly in the peritoneum or it can spread from another part of the body.

Infection of other parts of the body

Most often, peritonitis is caused by an infection that spreads to the peritoneum from another part of the body. This is known as secondary peritonitis.

Common causes of secondary peritonitis include:

• a split stomach ulcer
• a burst appendix
• acute pancreatitis (inflammation of the pancreas)
• severe trauma to the abdomen, such as a knife or gunshot wound
• digestive disorders, such as Crohn’s disease or diverticulitis

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.

Direct infection

Less commonly, peritonitis occurs when the peritoneum becomes directly infected. This is known as primary or spontaneous peritonitis.

In most cases, primary peritonitis is caused by scarring of the liver or peritoneal dialysis.

Cirrhosis

Scarring of the liver, known as cirrhosis, can occur due to liver damage. The most common causes of cirrhosis in the UK are alcohol misuse, a hepatitis C infection or obesity.

Cirrhosis can lead to a build-up of fluid inside the abdomen (known as ascites). This fluid is particularly vulnerable to infection and provides an environment where bacteria or fungi can grow and spread.

This build-up of fluid affects around half of people with cirrhosis, usually many years after cirrhosis was 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.

Although uncommon, peritonitis can occur if the equipment becomes contaminated by bacteria or fungi.

Serious complications of peritonitis can occur if the infection spreads to other parts of the body.

You will usually be admitted to hospital if you are diagnosed with peritonitis, so any problems can be identified and treated as quickly as possible.

Sepsis

Sepsis can occur if the infection spreads through the blood (septicaemia) 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 intravenous fluid therapy (fluids into a vein) and antibiotic injections.

If sepsis is not treated promptly, it can develop into septic shock.

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 and an 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.

Peritonitis can often be diagnosed after a physical examination and tests.

Physical examination

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

If you have peritonitis, parts of the body such as the abdominal (tummy) 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 tests.

Tests

You may need blood tests and urine tests to check for infection.

If you have a build-up of fluid in your abdomen (tummy), a small sample may be removed using a thin needle so it can be checked for signs of infection.

Doctors may also recommend:

• an X-ray – where radiation is used to produce an image, in order to look for evidence of leakage of air from the bowel
• an ultrasound scan – where sound waves are used to build a picture of the inside of your peritoneum
• a computerised tomography (CT) scan – a series of X-rays are taken to build up a more detailed three-dimensional picture of your peritoneum

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.

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 is regarded a medical emergency and requires immediate treatment. 

Signs of peritonitis often develop quickly and can include:

• sudden abdominal pain that becomes more severe
• nausea (feeling sick)
• a lack of appetite
• a high temperature (fever) of 38°C (100.4°F) 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 is not 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

Less commonly, an infection develops directly within the peritoneum due to:

• 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 is a serious condition that 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 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.

Read more about diagnosing peritonitis and treating peritonitis.

Complications

Peritonitis can be fatal, despite the best efforts of medical staff. This is often due to the infection spreading through the bloodstream to the major organs (septic shock).

It’s estimated that about 1 in every 10 people with peritonitis due to 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 is still a serious condition.

Read more about the possible complications of peritonitis.

Abdominal (tummy) pain is one of the main symptoms of peritonitis.

This usually begins as a sudden ache that progresses to a severe pain.

Other possible symptoms include:

• nausea (feeling sick)
• vomiting
• lack of appetite
• chills
• a high temperature (fever) of 38°C (100.4°F) or above
• rapid heartbeat
• not passing any urine or passing less than normal
• swelling of the abdomen

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.

If peritonitis is due to cirrhosis, you may not have any pain at all. You may simply feel generally unwell or develop other complications of liver disease such as increasing fluid accumulation in your abdomen or confusion.

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 on 0845 4647 or your local out-of-hours service.

If you’re diagnosed with peritonitis, you will probably be admitted to hospital so you can be carefully monitored.

This is because of the risk of serious complications of peritonitis, such as blood poisoning.

Medication

The initial treatment for peritonitis involves injections of antibiotics or antifungal medication. This 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 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 filtering machine) until the peritonitis has been successfully treated.

If peritonitis is causing pain, you may also be given painkilling medication.

Nutritional support

Many people with peritonitis have problems digesting and processing food, so a feeding tube may be needed.

The feeding tube is either passed into your stomach through your nose (nasogastric tube) or surgically placed into your stomach through your tummy.

If these are unsuitable, nutrition may be given directly into one of your veins (parenteral nutrition).

Surgery

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 that need to be drained with a needle. This is carried out using an ultrasound scanner to guide the needle to the abscess. Local anaesthetic is usually used so you don’t feel any pain. 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.