Spontaneous bacterial peritonitis (SBP) is an infection of abdominal fluid, known as ascites. This infection occurs without an obvious internal source, like a digestive tract perforation. SBP is a complication associated with advanced liver disease, which creates the conditions for infection to develop. The presence of ascites is a primary risk factor, as this fluid can become a breeding ground for bacteria, and the condition requires prompt medical intervention.
Underlying Causes of Spontaneous Bacterial Peritonitis
Advanced liver disease, particularly cirrhosis, is the most frequent cause of SBP. Cirrhosis scars the liver, obstructing blood flow and leading to portal hypertension—increased pressure in the portal vein. This pressure forces fluid from the liver and intestines into the abdominal cavity, creating ascites.
A factor in SBP development is bacterial translocation. This process involves bacteria, like Escherichia coli from the gut, migrating across the intestinal wall and into the ascitic fluid. In patients with advanced liver disease, compromised immune function prevents the neutralization of these bacteria, making them more susceptible to infection.
Other conditions that cause ascites, such as heart failure and nephrotic syndrome, also increase the risk of SBP. A low concentration of protein in the ascitic fluid is another risk factor. Patients with fluid protein levels below 1 g/dL are at higher risk because proteins are part of the fluid’s natural defense against bacteria.
Recognizing the Symptoms
The signs of SBP can be pronounced or subtle, and some individuals may show no obvious symptoms. The most common indicators are fever, chills, and abdominal pain or tenderness. A person might also feel unwell, with nausea and vomiting.
SBP can also trigger symptoms related to declining liver function. A new or worsening state of confusion or disorientation, known as hepatic encephalopathy, can occur because the infected liver is less able to clear toxins from the blood.
Other indicators include a decline in kidney function. Some individuals may develop an ileus, where the bowels become sluggish, leading to bloating and an inability to pass stool or gas. The presence of these symptoms in someone with known liver disease and ascites warrants immediate medical attention.
The Diagnostic Process
Confirming a diagnosis of SBP relies on analyzing the ascitic fluid, obtained through a diagnostic paracentesis. During this procedure, a physician inserts a thin needle into the patient’s abdomen to withdraw a small sample of the fluid. This procedure is performed to evaluate the cause of ascites or to check for infection.
The collected fluid is sent to a lab for a cell count to measure the white blood cells. Doctors look for an elevated count of polymorphonuclear leukocytes (PMNs), or neutrophils. A PMN count of 250 cells/mm³ or higher is the diagnostic threshold for SBP.
A portion of the fluid is also used for a bacterial culture to encourage any bacteria to grow. Identifying the specific bacteria helps confirm the diagnosis and ensure the chosen antibiotic is effective. Treatment is started based on the PMN count alone, without waiting for culture results, which can take a few days.
Treatment Protocols
Treatment for SBP begins immediately based on a presumptive diagnosis from the ascitic fluid cell count. The standard of care is the prompt administration of broad-spectrum intravenous (IV) antibiotics. These are effective against a wide range of bacteria since the specific organism is unknown when treatment begins. Cefotaxime is a commonly used antibiotic for SBP.
A part of the treatment protocol for many patients is the administration of intravenous albumin. Albumin is a protein produced by the liver, but its levels are often low in patients with advanced liver disease. Giving albumin alongside antibiotics has been shown to be beneficial in protecting kidney function, as kidney impairment is a frequent complication of SBP.
Albumin is recommended for patients with signs of more severe illness, such as high bilirubin levels or kidney dysfunction. The regimen involves administering a dose of albumin on the first day of treatment and a smaller dose on the third day. This therapy helps maintain blood volume and support organ function, improving survival rates.
Prevention of Recurrence and Outlook
After successful treatment for an SBP episode, the focus shifts to preventing another infection. The risk of recurrence is high, with the probability of another episode within one year reaching up to 70% without preventive measures. To reduce this risk, patients are prescribed a long-term, low-dose daily antibiotic, a strategy known as secondary prophylaxis.
The most commonly used antibiotic for this purpose is norfloxacin, which has been shown to decrease the probability of recurrence. This preventative treatment is continued indefinitely unless the patient’s underlying condition improves. The goal of this continuous therapy is to suppress the growth of intestinal bacteria and reduce their chances of translocating into the ascitic fluid.
An SBP episode is an event in the progression of chronic liver disease, signaling that the liver is struggling to perform its functions. Because of this, developing SBP is an indication for a patient to be evaluated for a liver transplant. A transplant is the only definitive cure for end-stage liver disease and, by extension, the risk of SBP.