Peritonitis - Causes of peritonitis

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.