Intra-abdominal infections (IAIs) comprise a wide range of pathological conditions, such as appendicitis, diverticulitis, gastroduodenal perforation, cholangitis, cholecystitis, and pancreatitis. IAIs are typically subcategorized as either uncomplicated or complicated, although the distinction between them is not always clear. Generally, uncomplicated IAIs involve a single organ and treatment includes surgical resection and perioperative prophylaxis only. Complicated IAIs (CIAIs) occur when the infection extends outside the organ that is the source of the infection into the peritoneal cavity. Most CIAIs involve peritonitis or intra-abdominal abscesses.
IAIs can also be classified as either community-acquired or healthcare-associated. Community-acquired IAIs develop in individuals that have not undergone recent surgical intervention or hospitalization. It is estimated that appendicitis and diverticulitis together comprise more than 80 percent of all community-acquired CIAIs. In contrast, healthcare-associated infections appear 48 hours or more after hospital admission, often during treatment for other conditions or as a post-surgical complication. Although most intra-abdominal infections are community-acquired, healthcare–associated pathogens are of increasing concern given the rising threat of resistant bacteria.
As CIAIs are often caused by resident gastrointestinal flora, their microbial etiology depends on the level of disruption of the gastrointestinal tract, where the number of microorganisms increases further down the gastrointestinal tract. Predominant pathogens include enteric gram-negative bacilli, gram-positive cocci, and anaerobic microorganisms.