Abdominal Infection

Abdominal infections represent a serious medical condition that can range from simple inflammation within the digestive tract to severe, life-threatening complications requiring emergency treatment. These infections are the second most common cause of infectious deaths in intensive care units and can lead to serious conditions like sepsis if not treated promptly.

Table of contents

• What Is an Abdominal Infection?
• Types of Abdominal Infections
• What Causes Abdominal Infections?
• Signs and Symptoms
• How Are Abdominal Infections Diagnosed?
• Treatment Approaches
• Understanding Severity and Complications
• Common Bacteria Involved

What Is an Abdominal Infection?

An abdominal infection, also called intra-abdominal infection, is a condition where harmful microorganisms cause inflammation in the belly area. This happens when bacteria or other germs invade the space inside your abdomen, leading to the buildup of infected fluid and causing your body’s defense system to react^[1].

These infections can affect different parts of your belly, including the space around your organs, the organs themselves, or the thin tissue layer called the peritoneum that lines the inside of your abdomen. When this tissue becomes inflamed, the condition is called peritonitis^[2].

Types of Abdominal Infections

Medical professionals classify abdominal infections into different categories based on how far the infection has spread and what caused it^[1].

Uncomplicated infections involve inflammation within the wall of the digestive tract without breaking through into the surrounding space. While these are often easier to treat, they can progress to more serious infections if treatment is delayed or if a particularly aggressive germ is involved^[1].

Complicated infections extend beyond the organ where they started and spread into the space around organs in your belly. These are associated with more serious conditions and can present as either localized areas of infection or widespread inflammation throughout the abdomen^[1].

Healthcare providers also classify abdominal infections by location. Intraperitoneal abscesses can develop below the diaphragm (the muscle that helps you breathe), around the intestines, in the pelvis, or near the stomach. Retroperitoneal abscesses affect organs like the kidneys or pancreas. Visceral abscesses occur within solid organs such as the spleen or liver^[3].

Peritonitis itself can be categorized as primary, secondary, or tertiary. Primary peritonitis, formerly called spontaneous bacterial peritonitis, occurs without any hole in the digestive tract and typically affects people with liver disease and fluid buildup in the belly, or those with certain kidney or autoimmune conditions^[10]. Secondary peritonitis happens when there is a rupture or hole in an abdominal organ^[2].

What Causes Abdominal Infections?

Most abdominal infections result from conditions that cause inflammation and holes in the digestive tract. Common causes include appendicitis, peptic ulcer disease, and diverticulitis^[1].

When bacteria enter your body and reach the abdominal space, your immune system sends white blood cells to fight them off. This battle causes inflammation that can kill nearby tissue. When tissue dies, a pocket forms and fills with pus (a thick fluid containing dead cells and bacteria), creating what doctors call an abscess^[3].

You may develop an abdominal infection if you have a bacterial infection that starts in your belly, have conditions like Crohn’s disease, diverticulitis, or pelvic inflammatory disease that cause inflammation, develop an infection after abdominal surgery, or have an injury such as a gunshot wound or stab wound that allows bacteria into your belly^[3].

Spontaneous bacterial peritonitis can happen when someone has liver disease such as cirrhosis or kidney disease^[2].

Signs and Symptoms

The symptoms of abdominal infections can vary depending on where the infection is located in your belly^[3].

Common symptoms include belly pain or tenderness, bloating, fever, loss of appetite, nausea, and unexplained weight loss^[2][3]. The pain may be new, severe, and constant, and might be felt in your upper abdomen, lower back, shoulder, or chest^[3].

In cases of peritonitis, patients may experience severe abdominal pain and tenderness that worsens with movement or touch^[2].

How Are Abdominal Infections Diagnosed?

A healthcare provider will perform a physical examination and ask about your symptoms. They will also order blood tests and imaging studies to confirm the diagnosis^[3].

A complete blood count helps check for signs of infection in your blood. Imaging tests are crucial for identifying abdominal infections and may include an abdominal ultrasound, chest X-ray, computed tomography (CT) scan of your abdomen and pelvis (the most common test), or magnetic resonance imaging (MRI) scan^[3].

CT scanning should be performed to determine whether an abdominal infection is present in adults who are not undergoing immediate surgery. However, further diagnostic imaging is not necessary in patients with obvious signs of widespread peritonitis who require immediate surgical intervention^[5].

Your provider may also do a fine needle aspiration to get a sample of pus from an abscess. A specialist will then test this sample to identify which bacteria are causing the infection^[3].

For patients with certain types of abdominal infections, doctors should obtain cultures from the infection site. The specimen should be representative of the material associated with the infection and should be of sufficient volume. These cultures help determine which antibiotics will work best and identify any resistant bacteria^[5].

Treatment Approaches

Successful treatment of abdominal infections requires three main components: early recognition of the infection source, control of the infection through procedures or surgery, and appropriate antibiotic treatment^[1].

The treatment for an abdominal abscess typically combines antibiotics to fight the infection and a procedure to drain pus from the abscess. Your healthcare provider may recommend percutaneous abscess drainage, which involves placing a drain or tube into the abscess so pus can flow into a connected bag. The provider uses a CT scan or MRI scan to guide the tube into place. You may receive local numbing medicine before the procedure so you’re awake but don’t feel pain^[3].

A source control procedure to drain infected areas, control ongoing contamination of the abdominal space, and restore normal function is recommended in virtually all patients with abdominal infections. Emergency surgery should be performed in patients with widespread peritonitis, even if measures to stabilize the patient must continue during the procedure^[5].

Select patients with minimal health problems and a well-contained area of infection can be treated with antibiotics alone without a source control procedure if close medical follow-up is possible^[5].

For community-acquired infections that are mild to moderate, doctors typically prescribe antibiotics effective against common bacteria found in the community. The specific antibiotics chosen depend on the severity of infection and whether it developed in the community or in a healthcare setting^[4].

In most cases, antibiotics should be stopped four days after the infection source has been controlled. If source control cannot be achieved, consultation with an infectious disease specialist is recommended^[4].

Rapid restoration of fluids into the bloodstream should be undertaken in patients with signs of dehydration or low blood pressure. In patients with septic shock (a life-threatening condition where blood pressure drops dangerously low), treatment to restore fluids should begin immediately. Intravenous fluid therapy should begin as soon as an abdominal infection is suspected^[5].

Understanding Severity and Complications

Abdominal infections represent an important cause of illness and death in hospital settings. Among patients who develop widespread peritonitis, many may progress to severe sepsis, which is defined as a severe body-wide inflammatory response to infection that is associated with sudden organ malfunction^[1].

Without treatment, abdominal infections can lead to serious, life-threatening conditions like sepsis and organ failure^[3]. It’s important to get treatment fast because healthcare professionals have effective ways to clear out the infection and treat any medical problem causing it^[2].

Recent studies have associated severe abdominal infections with significant death rates. While clinical trials often report mortality rates of two percent or less, real-world mortality may exceed twenty percent in critically ill patients, usually due to multiple organ failure^[10].

Common Bacteria Involved

Different types of bacteria cause abdominal infections, and knowing which bacteria are involved helps doctors choose the right antibiotics^[4].

In community-acquired infections, the most common bacteria include E. coli, Klebsiella, B. fragilis (a type of bacteria that grows without oxygen), and various Streptococci species^[4].

Healthcare-associated infections may involve the same community bacteria plus additional concerning germs like S. aureus, Enterococci, and P. aeruginosa. In higher-risk patients, particularly those who have received previous antibiotics, doctors should obtain cultures to identify any resistant bacteria^[4].

For spontaneous bacterial peritonitis, common bacteria include E. coli, Klebsiella species, and Streptococci species^[4].

Liver abscesses are commonly caused by E. coli, Klebsiella, and bacteria from the Strep milleri group^[4].