Peritonitis is a serious medical condition involving inflammation of the peritoneum, the thin membrane that lines the inside of your abdomen and covers most of your abdominal organs. This condition requires immediate medical attention, as delays in treatment can lead to life-threatening complications including sepsis and organ failure.

Understanding Peritonitis

The peritoneum is a delicate, thin layer of tissue that serves an important role in your body. It lines the inner walls of your abdomen and wraps around organs like the stomach, liver, and intestines. This membrane normally contains a small amount of lubricating fluid that allows your internal organs to move smoothly against each other during digestion and other bodily functions. When this normally sterile environment becomes inflamed—usually due to infection—the condition is called peritonitis.^[1]

Peritonitis represents a medical emergency that demands swift recognition and treatment. Without prompt intervention, the inflammation can trigger a cascade of dangerous changes throughout your body. The infection can spread rapidly, potentially causing sepsis, which occurs when your body has an extreme, life-threatening reaction to an infection. This can lead to tissue damage, organ failure, and death if not treated urgently.^[2]

The condition manifests in different forms depending on its origin. Healthcare providers classify peritonitis into three main types: primary (or spontaneous), secondary, and tertiary. Primary peritonitis occurs when bacteria reach the peritoneum through the bloodstream or lymphatic system, without any obvious source inside the abdomen. Secondary peritonitis, the most common form, happens when infection spreads from a damaged organ within the abdomen. Tertiary peritonitis refers to persistent or recurring infection that continues even after initial treatment attempts.^[4][6]

Epidemiology

Determining the exact number of peritonitis cases worldwide remains challenging due to variations in how the condition is reported and tracked. However, medical research provides important insights into who is most affected. Studies have found that intra-abdominal infections, which include peritonitis, occur in approximately 25% of patients with multiple organ failure in surgical intensive care units. When examining autopsy records, peritonitis was present in about 8% of all cases reviewed.^[13]

The likelihood of developing peritonitis varies significantly based on underlying health conditions. People with chronic liver disease, particularly those with cirrhosis (severe scarring of the liver), face substantial risk. Spontaneous bacterial peritonitis affects an estimated 10% to 30% of patients with alcoholic cirrhosis.^[12] This type of peritonitis develops when fluid accumulates in the abdomen—a condition called ascites—and becomes infected.

Another group at increased risk includes individuals receiving peritoneal dialysis for kidney failure. This treatment method requires inserting a catheter into the abdominal cavity to filter waste from the blood. Patients on chronic ambulatory peritoneal dialysis experience, on average, one episode of peritonitis every 33 months.^[12] This connection between dialysis and infection risk makes proper hygiene and catheter care essential for these patients.

Historical data shows how treatment advances have dramatically improved survival. In the early 1900s, mortality rates from peritonitis reached 80% to 100%. By 1926, surgical interventions had reduced this to about 60%. Today, with modern antibiotics, surgical techniques, and intensive care, the average mortality rate has decreased to approximately 30% to 40%.^[13] Despite these improvements, peritonitis remains a serious condition that requires urgent medical intervention.

Causes

Bacterial infections represent the most common cause of peritonitis. These infections typically originate in two ways: either bacteria spread from another organ in your abdomen (secondary peritonitis), or bacteria enter your peritoneum directly through your bloodstream or medical equipment (primary peritonitis).^[1][2]

Secondary peritonitis develops when an abdominal organ becomes damaged, allowing bacteria and infected material to leak into the normally sterile peritoneal cavity. This can happen through various mechanisms. A ruptured appendix is a common culprit—when the appendix becomes inflamed with appendicitis and then bursts, bacteria-laden pus spills into the abdomen. Similarly, severe stomach ulcers can burn completely through the stomach wall, creating a hole called a perforation that allows digestive juices and bacteria to escape into the peritoneum.^[2][5]

Digestive diseases pose another significant risk. Conditions like diverticulitis (inflammation of small pouches in the intestine) or inflammatory bowel diseases such as Crohn’s disease can create holes in the gastrointestinal tract. When these perforations occur, intestinal contents containing billions of bacteria leak into the abdominal cavity, triggering severe inflammation.^[2][11]

In women, reproductive system problems can lead to peritonitis. A ruptured ectopic pregnancy—where a fertilized egg grows in the fallopian tube instead of the uterus—can cause the tube to burst, releasing infected material. Pelvic inflammatory disease involving a tubo-ovarian abscess that ruptures can similarly spread infection to the peritoneum.^[2][11]

Primary peritonitis, also called spontaneous bacterial peritonitis, occurs through a different mechanism. In this case, bacteria reach the peritoneum through the bloodstream or lymphatic vessels without any obvious hole or rupture in an abdominal organ. This typically happens in people with compromised immune systems or those with fluid buildup in the abdomen from conditions like cirrhosis, kidney failure, or heart failure. The accumulated fluid creates an environment where bacteria can grow, even without direct contamination from the gut.^[1][2]

Medical treatments can inadvertently introduce bacteria into the peritoneum. Peritoneal dialysis, which uses a catheter inserted into the abdominal cavity, provides a direct pathway for germs to enter if proper hygiene isn’t maintained. Similarly, feeding tubes placed to deliver nutrition directly into the stomach can sometimes allow bacteria to reach the peritoneal space.^[2][5]

Not all peritonitis results from bacterial infection. Sometimes called chemical or sterile peritonitis, inflammation can occur when certain body fluids leak into the peritoneum. Bile from a perforated gallbladder, stomach acid from a perforated ulcer, pancreatic enzymes from severe pancreatitis, or blood from internal bleeding can all irritate the peritoneum and cause inflammation even without bacteria present.^[1][2]

Risk Factors

Several groups of people face elevated risk for developing peritonitis. Understanding these risk factors helps identify who needs extra vigilance and preventive measures. People with chronic liver disease, especially those with cirrhosis, are particularly vulnerable. The scarring and damage to the liver often leads to fluid accumulation in the abdomen (ascites), which can become infected spontaneously without any obvious trigger. The weakened immune function that accompanies advanced liver disease further increases susceptibility to infection.^[1][11]

Individuals with kidney failure requiring dialysis face ongoing risk, particularly those using peritoneal dialysis. This treatment method requires maintaining a catheter in the abdominal cavity, creating a potential entry point for bacteria. Each connection and disconnection of dialysis equipment presents an opportunity for contamination if strict hygiene protocols aren’t followed. Patients with heart disease or cancer that causes ascites also belong to high-risk groups.^[1][5]

People with digestive system conditions carry increased risk. Those suffering from Crohn’s disease, ulcerative colitis, or diverticulitis have inflamed intestinal tissue that’s more prone to developing holes or perforations. Individuals with a history of peptic ulcers face similar concerns, as these ulcers can erode completely through the stomach or intestinal wall. Anyone who has had previous abdominal surgery has slightly elevated risk, as surgical sites can sometimes develop infections or complications that lead to peritonitis.^[2][11]

Traumatic injuries to the abdomen significantly increase peritonitis risk. Penetrating injuries from knives or gunshots obviously breach the abdominal cavity, but even blunt force trauma from car accidents or falls can damage internal organs enough to cause ruptures. The resulting contamination of the normally sterile peritoneal space with intestinal contents or blood can quickly lead to severe infection.^[2]

Women with certain reproductive health conditions also face heightened risk. Those with pelvic inflammatory disease, particularly if abscesses form in the fallopian tubes or ovaries, may develop peritonitis if these abscesses rupture. Women who experience ectopic pregnancies risk peritonitis if the pregnancy causes the fallopian tube to burst.^[2][11]

Immunocompromised individuals—those with weakened immune systems from conditions like HIV/AIDS, cancer treatment, or immunosuppressive medications—are more susceptible to infections that can lead to peritonitis. Their bodies have reduced ability to fight off bacteria that might contaminate the peritoneum. Similarly, elderly individuals and those with multiple chronic health conditions face greater risk due to diminished overall health and immune function.^[4]

Symptoms

Recognizing the symptoms of peritonitis can be lifesaving, as this condition requires emergency medical treatment. The most characteristic and alarming symptom is abdominal pain that often begins as a dull ache but rapidly intensifies into severe, constant pain. This pain typically worsens with any movement, including walking, coughing, or even breathing deeply. The discomfort becomes so intense that many people find they cannot sit still or find any comfortable position.^[2][8]

The abdomen usually becomes swollen, tight, and extremely tender to touch. Even gentle pressure on the belly causes significant pain. The abdominal wall may feel hard or rigid—a condition doctors call “board-like rigidity”—because the muscles reflexively tense up to protect the inflamed peritoneum beneath. This bloating results from fluid accumulation in the abdominal cavity and from decreased intestinal movement as the body tries to limit motion in the inflamed area.^[1][5]

Fever commonly accompanies peritonitis, signaling that the body is fighting an infection. The temperature elevation may be accompanied by chills and overall feelings of being unwell. The heart rate typically increases beyond normal levels as the body responds to infection and inflammation. Some people experience rapid, shallow breathing as the abdominal pain makes deep breathing uncomfortable.^[2][8]

Digestive symptoms frequently occur alongside the pain. Nausea and vomiting are common, as the inflamed peritoneum disrupts normal digestive function. Many people lose their appetite completely and feel unable to eat. Constipation develops as intestinal movement slows down or stops altogether—a condition called paralytic ileus, which represents temporary paralysis of the intestines. Some individuals may have difficulty passing gas. In contrast, others might experience diarrhea, particularly if the peritonitis stems from an intestinal infection.^[1][2][11]

As peritonitis progresses, people may develop signs of dehydration. These include extreme thirst, a dry mouth and tongue, decreased urination or inability to urinate, and rapid breathing. The skin may become pale or grayish. Fatigue and weakness intensify as the body diverts energy to fighting the infection. Some individuals become confused or disoriented as the infection affects their overall system.^[2][5]

For people receiving peritoneal dialysis, specific warning signs deserve immediate attention. The dialysis fluid that drains from the abdomen may appear cloudy instead of clear, or it might contain white flecks, strands, or clumps. The skin around the catheter insertion site may become red, swollen, warm, or painful. Pus might drain from this area. These signs indicate that bacteria have infected the peritoneal cavity through the dialysis equipment.^[1][5]

In severe cases, peritonitis can lead to signs of septic shock, including a very rapid or very slow heart rate, severe confusion or loss of consciousness, extremely low blood pressure, cold and clammy skin, and decreased or absent urine output. These symptoms indicate a medical emergency requiring immediate intervention, as septic shock can quickly become fatal without treatment.^[2][11]

Prevention

While not all cases of peritonitis can be prevented, many risk factors can be managed or avoided through careful attention to health and hygiene. For individuals receiving peritoneal dialysis, meticulous cleanliness represents the most important preventive measure. Washing hands thoroughly with soap and water before touching the dialysis catheter or any dialysis supplies is essential. The skin around the catheter exit site should be cleaned regularly and kept dry. Any signs of redness, drainage, or infection at this site require immediate medical attention before they progress to peritonitis.^[1][20]

People using peritoneal dialysis should keep the catheter end covered when not in use to prevent contamination. They should avoid swimming unless their dialysis team has specifically approved it, as water can introduce bacteria. If approved for swimming or bathing, the catheter and access site must be cleaned and dried thoroughly immediately afterward. Following all instructions from the dialysis team regarding connection techniques and sterile procedures helps minimize infection risk.^[20][21]

Managing underlying health conditions reduces peritonitis risk significantly. People with liver disease should work closely with their healthcare providers to control their condition and prevent complications like ascites. If fluid does accumulate in the abdomen, following medical advice about medications and monitoring can help prevent spontaneous bacterial infection. Individuals with inflammatory bowel disease, diverticulitis, or other digestive conditions should adhere to their treatment plans to reduce the likelihood of intestinal perforation.^[11]

Seeking prompt medical care for abdominal symptoms can prevent some cases of peritonitis. Appendicitis, if treated before the appendix ruptures, won’t lead to peritonitis. Similarly, early treatment of ulcers, gallbladder infections, or pelvic infections can prevent these conditions from progressing to the point where organs rupture or perforate. Anyone experiencing severe abdominal pain, particularly if it comes on suddenly or worsens rapidly, should seek immediate medical evaluation.^[1][11]

For people undergoing abdominal surgery, following post-operative care instructions helps prevent surgical site infections that could lead to peritonitis. This includes keeping incisions clean and dry, watching for signs of infection, taking any prescribed antibiotics as directed, and attending all follow-up appointments. Avoiding strenuous activities before the surgical site has fully healed reduces the risk of complications.^[2]

Individuals at high risk for peritonitis should maintain regular check-ups with their healthcare providers. Those with cirrhosis, kidney failure, or other chronic conditions benefit from ongoing monitoring that can detect early signs of problems before they become severe. Vaccinations to prevent infections may be recommended for immunocompromised individuals.^[11]

Pathophysiology

Understanding what happens inside the body during peritonitis helps explain why this condition causes such serious symptoms and requires urgent treatment. When bacteria or irritating substances enter the normally sterile peritoneal cavity, the body launches an immediate immune response. White blood cells rush to the area, and the peritoneal membrane begins releasing inflammatory chemicals. This inflammatory process is the body’s attempt to fight off the invaders, but it also causes significant problems.^[4][12]

The inflammation triggers blood vessels in the peritoneum to become more permeable, allowing fluid to leak from the bloodstream into the abdominal cavity. This fluid accumulation serves to dilute bacteria and toxins, but it also causes the characteristic abdominal swelling and bloating seen in peritonitis. As more and more fluid shifts from blood vessels into the abdomen—a process called third-spacing—the volume of fluid circulating in blood vessels decreases. This can lead to low blood pressure and reduced blood flow to vital organs.^[12]

The inflammatory response also affects the intestines. As the peritoneum becomes inflamed, intestinal muscles stop contracting normally. This condition, called paralytic ileus, means the digestive system essentially shuts down temporarily. Food and fluids can’t move through the intestines properly, leading to nausea, vomiting, inability to pass gas or stool, and further abdominal distention. The decreased intestinal movement prevents the body from absorbing nutrients and fluids, contributing to dehydration.^[2][12]

When bacteria multiply in the peritoneal cavity, they produce toxins that can enter the bloodstream. The body’s immune system responds by releasing inflammatory substances throughout the entire system, not just in the abdomen. This systemic inflammatory response can affect multiple organs simultaneously. The heart may beat faster as it tries to maintain adequate blood flow despite dropping blood pressure. The lungs may work harder, causing rapid breathing. The kidneys may produce less urine as blood flow to them decreases.^[2][6]

In severe cases, peritonitis triggers sepsis—a life-threatening condition where the body’s response to infection causes widespread inflammation and organ dysfunction. During sepsis, inflammatory chemicals cause blood vessels throughout the body to leak fluid. Blood pressure drops dangerously low, preventing adequate oxygen and nutrient delivery to tissues. Multiple organ systems can begin to fail, including the kidneys, liver, lungs, and heart. This multiple organ dysfunction syndrome represents the most serious complication of peritonitis and carries high mortality risk.^[2][13]

The type of bacteria involved influences the disease process. In secondary peritonitis following intestinal perforation, mixed bacterial infections are common. Initially, bacteria like Escherichia coli (E. coli) cause acute symptoms and can lead to severe sepsis. If the patient survives this initial phase, anaerobic bacteria like Bacteroides fragilis may cause abscess formation several days later. These different bacteria require different antibiotics for effective treatment.^[10]

The body attempts to contain the infection by forming adhesions—fibrous bands of tissue that wall off infected areas. While this can prevent infection from spreading throughout the entire abdomen, these adhesions can cause long-term complications, including chronic abdominal pain and bowel obstructions even after the infection resolves.^[11]