Chapter 121. Intraabdominal Infections and Abscesses (Part 2 )

Primary (Spontaneous) Bacterial PeritonitisPeritonitis is either primary (without an apparent source of contamination) or secondary. The types of organisms found and the clinical presentations of these two processes are different. In adults, primary bacterial peritonitis (PBP) occurs most commonly in conjunction with cirrhosis of the liver (frequently the result of alcoholism).However, the disease has been reported in adults with metastatic malignant disease, postnecrotic cirrhosis, chronic active hepatitis, acute viral hepatitis, congestive heart failure, systemic lupus erythematosus, and lymphedema as well as in patients with no underlying disease. ...
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Chapter 121. Intraabdominal Infections and Abscesses (Part 2 ) Chapter 121. Intraabdominal Infections and Abscesses (Part 2 ) Primary (Spontaneous) Bacterial Peritonitis Peritonitis is either primary (without an apparent source of contamination)or secondary. The types of organisms found and the clinical presentations of thesetwo processes are different. In adults, primary bacterial peritonitis (PBP) occursmost commonly in conjunction with cirrhosis of the liver (frequently the result ofalcoholism). However, the disease has been reported in adults with metastatic malignantdisease, postnecrotic cirrhosis, chronic active hepatitis, acute viral hepatitis,congestive heart failure, systemic lupus erythematosus, and lymphedema as wellas in patients with no underlying disease. Although PBP virtually always developsin patients with preexisting ascites, it is, in general, an uncommon event, occurringin ≤10% of cirrhotic patients. The cause of PBP has not been establisheddefinitively but is believed to involve hematogenous spread of organisms in apatient in whom a diseased liver and altered portal circulation result in a defect inthe usual filtration function. Organisms multiply in ascites, a good medium forgrowth. The proteins of the complement cascade have been found in peritonealfluid, with lower levels in cirrhotic patients than in patients with ascites of otheretiologies. The opsonic and phagocytic properties of PMNs are diminished inpatients with advanced liver disease. The presentation of PBP differs from that of secondary peritonitis. Themost common manifestation is fever, which is reported in up to 80% of patients.Ascites is found but virtually always predates infection. Abdominal pain, an acuteonset of symptoms, and peritoneal irritation during physical examination can behelpful diagnostically, but the absence of any of these findings does not excludethis often-subtle diagnosis. Nonlocalizing symptoms (such as malaise, fatigue, orencephalopathy) without another clear etiology should also prompt considerationof PBP in a susceptible patient. It is vital to sample the peritoneal fluid of anycirrhotic patient with ascites and fever. The finding of >250 PMNs/µL isdiagnostic for PBP, according to Conn(http://jac.oxfordjournals.org/cgi/content/full/47/3/369). This criterion does notapply to secondary peritonitis (see below). The microbiology of PBP is alsodistinctive. While enteric gram-negative bacilli such as Escherichia coli are mostcommonly encountered, gram-positive organisms such as streptococci,enterococci, or even pneumococci are sometimes found. In PBP, a single organismis typically isolated; anaerobes are found less frequently in PBP than in secondaryperitonitis, in which a mixed flora including anaerobes is the rule. In fact, if PBP issuspected and multiple organisms including anaerobes are recovered from theperitoneal fluid, the diagnosis must be reconsidered and a source of secondaryperitonitis sought. The diagnosis of PBP is not easy. It depends on the exclusion of a primaryintraabdominal source of infection. Contrast-enhanced CT is useful in identifyingan intraabdominal source for infection. It may be difficult to recover organismsfrom cultures of peritoneal fluid, presumably because the burden of organisms islow. However, the yield can be improved if 10 mL of peritoneal fluid is placeddirectly into a blood culture bottle. Since bacteremia frequently accompanies PBP,blood should be cultured simultaneously. No specific radiographic studies arehelpful in the diagnosis of PBP. A plain film of the abdomen would be expected toshow ascites. Chest and abdominal radiography should be performed in patientswith abdominal pain to exclude free air, which signals a perforation (Fig. 121-2). Figure 121-2 Pneumoperitoneum. Free air under the diaphragm on an upright chest film suggests the presenceof a bowel perforation and associated peritonitis. (Image courtesy of Dr. JohnBraver; with permission.)