Spontaneous Bacterial Peritonitis

Richard Basilan Key Points

• Spontaneous bacterial peritonitis usually occurs in the setting of ascites and chronic liver disease.

• Spontaneous bacterial peritonitis is a diagnosis of exclusion.

• Ascitic fluid culture yield improves with inoculation into blood culture bottles at bedside.

Spontaneous bacterial peritonitis (SBP) is a form of infectious peritonitis without a surgically correctable cause and is therefore a diagnosis of exclusion. The route of infection in SBP is usually not apparent and is often presumed to be hematogenous, lymphogenous, by transmural migration through an intact gut wall from the intestinal lumen, or in women, from the vagina via the fallopian tubes (Levison and Bush, 2010). SBP occurs in the setting of ascites in most cases, and it is particularly common in patients with cirrhosis. In pediatric populations, those with postnecrotic cirrhosis or nephrotic syndrome are more often affected. In adults, almost 70% of patients who develop SBP have Child-Pugh class C liver disease, and 10% to 30% of hospitalized patients with cirrhosis and ascites have SBP (Mowat and Stanley, 2001). SBP is almost always caused by a single organism, typically enteric gram-negative rods, most often E. coli, followed by Klebsiella pneumoniae. Gram-positive cocci account for about 25% of

Box 16-6 Minimal Diagnostic Workup to Qualify as Fever of Unknown Origin

Comprehensive history Physical examination

Complete blood cell count plus differential Blood film reviewed by hematopathologist

Routine blood chemistry (including lactate dehydrogenase, bilirubin, and liver enzymes)

Urinalysis and microscopy

Blood (x3) and urine cultures

Antinuclear antibodies, rheumatoid factor

Human immunodeficiency virus antibody

Cytomegalovirus IgM antibodies; heterophil antibody test (if consistent with mononucleosis-like syndrome) Q-fever serology (if exposure risk factors exist) Chest radiography

Hepatitis serology (if abnormal liver enzyme test result)

From Mourad O, Palda V, Detsky A. A comprehensive evidence-based approach to fever of unknown origin. Arch Intern Med 2003;163:545-551.

episodes of SBP, and streptococci are isolated most often. SBP caused by anaerobes is rare. Growth of more than one organism should raise the suspicion of secondary peritonitis.

Signs and symptoms of SBP are subtle and require a high index of suspicion. Fever greater than 100° F (38° C) is the most common presenting sign, occurring in 50% to 80% of cases. Abdominal pain, nausea, vomiting, and diarrhea are usually present. Peritoneal signs (abdominal tenderness or rebound tenderness) are common but may be absent in patients with ascites. In adults, mental status changes may also occur. SBP is often confused with acute appendicitis in children. In adults, SBP should be suspected in any patient with previously stable chronic liver disease who undergoes acute decompensation in clinical status.

Spontaneous bacterial peritonitis is diagnosed by analysis of ascitic fluid obtained by abdominal paracentesis. Infection has been typically defined as an ascitic fluid WBC count higher than 250 cells/mm3, which is considered diagnostic even when the culture of the ascitic fluid is negative. In cases where bloody fluid is obtained ("traumatic paracentesis"), the WBC count should be corrected by 1 WBC per 250 RBCs/mm3. The use of bedside dipstick for leukocyte esterase has a high false-negative rate and is not recommended (Nguyen-Khac et al., 2008). Ascitic fluid culture yield can be increased by inoculating blood culture bottles with 10 mL of ascitic fluid at the bedside. Blood cultures should also be obtained as part of the workup.

After the diagnosis of peritonitis is established, secondary peritonitis should be ruled out. CT of the abdomen with oral and intravenous contrast can help direct the surgeon to a particular source of infection, as opposed to doing a full exploratory laparotomy. A high ascitic fluid total protein (>1 g/dL) or amylase level is suggestive of secondary peritonitis. The treatment of choice is generally a third-generation cephalosporin such as cefotaxime (2 g IV every 8-12 hours) or ceftriaxone (2 g IV once daily). Patients who have an ascitic fluid WBC count higher than 250 cells/mm3 should be given empiric intravenous antibiotics without delay. Oral amoxi-cillin-clavulanic acid can be used for mild, uncomplicated cases (Navasa et al., 1996). Duration of treatment varies from 5 to 14 days depending on clinical response. Patients usually respond to appropriate antibiotic therapy within 48 to 72 hours; otherwise, a repeat paracentesis should be performed. If the ascitic fluid WBC count does not decrease by more than 25%, alternative diagnoses should be considered. Prophylaxis with a fluoroquinolone or trimethoprim-sulfa-methoxazole should be considered, particularly in high-risk patients (Garcia-Tsao and Lim, 2009).

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