Peritonitis is defined as an inflammation of the serosal membrane that lines the abdominal cavity and the organs contained therein. The peritoneum, which is an otherwise sterile environment, reacts to various pathologic stimuli with a fairly uniform inflammatory response. Depending on the underlying pathology, the resultant peritonitis may be infectious or sterile (ie, chemical or mechanical). Intra-abdominal sepsis is an inflammation of the peritoneum caused by pathogenic microorganisms and their products.[1] The inflammatory process may be localized (abscess) or diffuse in nature. 

Signs and Symptoms

The signs and symptoms of peritonitis include:

Swelling and tenderness in the abdomen with pain ranging from dull aches to severe, sharp pain

Fever and chills

Loss of appetite

Thirst

Nausea and vomiting

Less urine

Not being able to pass gas or stool

Diagnosis

Peritonitis is an emergency and can be life threatening. Your doctor will do a physical examination to see whether you need surgery to fix the underlying problem. The doctor will feel and press your abdomen to find any swelling and tenderness, and look for signs that fluid has collected in the area. The doctor may listen to bowel sounds and check for:

Difficulty breathing

Low blood pressure

Signs of dehydration

The following procedures also may be performed:

Blood tests, to see if there is bacteria in your blood

Test samples of fluid from the abdomen, to identify the bacteria causing the infection

CT scan, to identify fluid in the abdomen, or an infected organ

X-rays, to spot air in the abdomen, which means that an organ may be torn or perforated

Source:

https://umm.edu/health/medical/altmed/condition/peritonitis

http://emedicine.medscape.com/article/180234-overview