Peritonitis is inflammation and usually infection of the abdominal cavity and its lining. There are two major types of peritonitis. These ares :-

1) Primary peritonitis and
2) Secondary peritonitis

Primary peritonitis is caused by the spread of an infection from the blood and lymph nodes to the peritoneum. Secondary peritonitis which is the more common type of peritonitis is caused by the entry of bacteria or enzymes into the peritoneum from the gastrointestinal or biliary tract.

Causes

Peritonitis usually results from perforation (tear or damage) to a part of the intestine so that the contents escape and get into the peritoneum and infect it. Primary peritonitis usually occurs in people who have an accumulation of fluid in their abdomens (ascites). Ascites is a common complication of severe cirrhosis of the liver (a disease in which the liver grows increasingly scarred and dysfunctional). The fluid which accumulates creates a good environment for the growth of bacteria.
Sometimes a bit of stool may become lodged in one of the pouches, leading to infection. A small tear or perforation can also develop in an infected pouch, which in turn can cause an infection within your abdomen.

Symptoms

Usually, vomiting, a fever (100.5 F [38.0 C] or higher), and abdominal tenderness occur. Other symptoms depend on whether infection follows inflammation and on the type and extent of the infection. Pain may be limited to a small area of the abdomen or may be present throughout the abdomen. Abdominal pain is usually severe.
Major symptoms of peritonitis are:
Board-like rigidity of the abdomen, due to contraction of the muscles of the abdominal wall
Chills and fever, with profuse perspiration
Nausea and vomiting
Weakness
Pale, cold skin
Shock

Treatment

Treatment typically involves surgery and antibiotics. In cases associated with peritoneal dialysis, antibiotics may be infused through the dialysis catheter, but if the infection is severe, the catheter itself must often be removed.
Treatment options for peritonitis depend on the cause, but may include:
Hospitalisation often in an intensive care unit.
Antibiotics tailored to the specific bacteria to kill the infection.
Intravenous fluids to rehydrate the body and replace lost electrolytes.
Surgery to repair the ruptured organ and wash out the abdominal cavity of blood and pus.
Treatment for the underlying cause such as a perforated ulcer.

Surgery is often necessary when peritonitis is due to a disorder that has caused perforation along the intestinal tract, for example, a peptic ulcer or a burst appendix.