Peritonitis is an inflammation of the peritoneum, the thin membrane that lines the inside of your abdomen and covers most of your abdominal organs. It’s almost always caused by a bacterial infection, and it’s a medical emergency. Without prompt treatment, the infection can spread into the bloodstream and cause life-threatening organ failure.
The Peritoneum and Why It Matters
Your peritoneum is a smooth, two-layered membrane made of cells that secrete a small amount of fluid. One layer (the parietal peritoneum) lines the walls of your abdomen and pelvis. The other (the visceral peritoneum) wraps around your organs, including your stomach, intestines, liver, and spleen. The thin film of fluid between the two layers lets your organs glide against each other without friction.
Because the peritoneum is so large and has a rich blood supply, an infection here can escalate quickly. Bacteria or other irritants that reach this membrane trigger intense inflammation, and the body responds with pain, swelling, and fluid buildup that can progress to sepsis within hours.
Two Main Types
Spontaneous Bacterial Peritonitis
This type develops without any rupture or tear in an organ. It occurs most often in people with advanced liver disease (cirrhosis), which causes large amounts of fluid to accumulate in the abdomen, a condition called ascites. That standing fluid becomes a breeding ground for bacteria. More than 90% of spontaneous cases involve a single type of bacterium, most commonly E. coli (about 40% of cases) or species of Streptococcus.
Secondary Peritonitis
This is by far the more common form. It happens when something ruptures or leaks inside the abdomen, spilling bacteria-laden contents directly onto the peritoneum. Common triggers include a burst appendix, a perforated stomach ulcer, a hole in the colon from diverticulitis, severe pancreatitis, or abdominal trauma. Certain medical procedures also carry a small risk, particularly peritoneal dialysis, abdominal surgery, and the use of feeding tubes. Colonoscopy and endoscopy can cause it too, though that’s rare.
Unlike spontaneous peritonitis, secondary peritonitis is almost always polymicrobial, meaning a mix of aerobic and anaerobic bacteria are involved, with gram-negative organisms predominating.
Symptoms to Recognize
The hallmark of peritonitis is severe abdominal pain that gets worse with movement. The pain is often diffuse, spreading across the entire abdomen rather than staying in one spot. Other common symptoms include:
- Abdominal tenderness and rigidity. Your abdominal muscles may involuntarily tighten when the area is touched, a response called guarding.
- Rebound tenderness. The pain actually worsens when pressure on the abdomen is released, not when it’s applied. This is a classic sign of peritoneal irritation.
- Fever and chills.
- Nausea, vomiting, and bloating.
- Loss of appetite and an inability to pass gas or stool. The bowel often stops moving normally in response to the inflammation.
In people on peritoneal dialysis, one of the earliest signs is cloudy dialysis fluid draining from the abdomen. For people with cirrhosis and ascites, the symptoms can be subtler, sometimes presenting as worsening confusion or a general decline rather than dramatic abdominal pain.
How It’s Diagnosed
Doctors typically start with a physical exam, pressing on the abdomen to check for tenderness, rigidity, and rebound pain. Blood tests look for signs of infection and organ stress. If spontaneous bacterial peritonitis is suspected, a sample of abdominal fluid is drawn with a needle and analyzed. A count of more than 250 infection-fighting white blood cells (neutrophils) per cubic millimeter in that fluid confirms the diagnosis.
Imaging plays a key role in secondary peritonitis. X-rays can reveal free air under the diaphragm, a telltale sign that an organ has perforated. Ultrasound can detect fluid collections and abscesses. CT scans provide the most detailed picture and help pinpoint exactly where the problem started.
Treatment: Antibiotics and Surgery
Treatment begins with intravenous antibiotics, started as soon as peritonitis is suspected and often before exact test results come back. For spontaneous bacterial peritonitis in people with liver disease, a class of antibiotics called cephalosporins is the standard first choice. For secondary peritonitis, broader combinations are used to cover the wider range of bacteria involved.
The duration of antibiotics depends on severity. Uncomplicated cases where the source of infection is quickly controlled may need only 5 to 7 days. Milder situations, like early appendicitis caught before significant spillage, might require as little as 24 to 72 hours of post-surgical antibiotics. More stubborn infections, particularly those involving certain fungal or staph organisms, can require 2 to 3 weeks of treatment.
Surgery is frequently necessary in secondary peritonitis. The goals are straightforward: find and fix the source of contamination (repair the perforation, remove the ruptured appendix, drain an abscess), clean out infected material, and prevent the infection from recurring. In cases of a ruptured appendix, perforated colon, or ischemic bowel, the need for surgery is obvious and urgent. Delays in operating when abdominal sepsis is severe lead to significantly worse outcomes and a higher chance of needing repeat operations.
In the most severe cases, surgeons may leave the abdomen partially open after the initial operation. This open-abdomen approach allows direct access for repeated cleanings and inspections over the following days until the infection is under control.
Complications and Risks
The biggest danger is sepsis, the body’s overwhelming response to infection. When bacteria from the peritoneum enter the bloodstream, they can trigger a cascade that leads to dangerously low blood pressure, organ failure, and death. The speed at which peritonitis can progress from a localized abdominal problem to a systemic crisis is what makes it a true emergency.
Other complications include abdominal abscesses (pockets of pus that may need separate drainage), bowel obstruction from scar tissue that forms during healing, and, in people with cirrhosis, worsening liver and kidney function. People who survive a first episode of spontaneous bacterial peritonitis have a high risk of recurrence and are often placed on long-term preventive antibiotics.
Recovery Timeline
How quickly you recover depends heavily on what caused the peritonitis and how early treatment began. Someone who had early appendicitis caught and treated promptly may be home from the hospital within days. A person who needed emergency surgery for a perforated colon with widespread contamination could face weeks of hospitalization, possibly including time in intensive care.
Even after the peritonitis itself is resolved, recovery from the underlying condition often takes longer. A person with cirrhosis who develops spontaneous bacterial peritonitis, for example, faces an ongoing battle with liver disease that extends well beyond the acute infection. For secondary peritonitis that required major surgery, full physical recovery, including regaining strength and returning to normal eating, can take several weeks to months.