Infectious Diseases I

Complicated intra-abdominal infection spans prehospital and in-hospital dispositions and a variety of

pathogenic processes involving several organ systems.

illness. Appendicitis is the most prevalent cause of complicated intra-abdominal infection. Recent

controlled trials and large international observational sepsis studies report abdominal infection as the

second or third most common source of sepsis, accounting for 21% of sepsis and 30% of septic shock

cases.

Complicated intra-abdominal infection is the second most common cause of mortality in critically ill

patients. Crude mortality for primary intra-abdominal infection is almost 30%, whereas rates exceed

50% in patients with secondary intra-abdominal infection. Those presenting with sepsis caused by

intra-abdominal infection have crude mortality above 40%.

The IDSA and Surgical Infection Society (SIS) jointly published guidelines for the management of

intra-abdominal infection in 2010. In 2017, the Surgical Infection Society updated these guidelines,

including management for complicated intra-abdominal infection, which are reflected throughout this

section. As an additional resource, an international group published recommendations in 2021 on a

global approach to diagnosis and management of specific intra-abdominal infections (World J Emerg

Surg 2021;16:49).

of origin into the peritoneal space and is associated with either abscess formation or peritonitis. These

infections usually arise from spillage of viscus-related fluid and flora into the peritoneal cavity, causing

inflammation and injury to the peritoneal membrane. Retroperitoneal infections also are possible, but

these are related to the individual retroperitoneal organ rather than the peritoneum.

Peritonitis is described as primary, secondary, and tertiary.

Primary peritonitis, or spontaneous bacterial peritonitis, is peritonitis related to bacterial

translocation of proximal small bowel overgrowth and not peritoneal disruption or organ

perforation. Primary peritonitis is generally diffuse in nature.

Secondary peritonitis is caused by leakage of intraluminal fluid and microorganisms secondary to

macro- or microperforation of the GI tract. Secondary peritonitis can be diffuse or localized to an

organ, depending on the extent of peritoneal involvement. Causes of secondary peritonitis include

direct trauma, ischemia, thrombosis, ulceration, malignancy, and anastomotic leak.

Tertiary peritonitis is peritonitis that persists or recurs at least 48 hours after the management of

primary or secondary peritonitis. Tertiary peritonitis can represent a new intra-abdominal process

or host, anatomic, or therapeutic failure of treatment of primary or secondary peritonitis.

Pathogens associated with complicated intra-abdominal infections and peritonitis are influenced by type/

cause of peritonitis, MDRO risk factors, previous antibiotic exposure, and patient-specific colonization.

Patients having health care–associated intra-abdominal infections more often tend to have antibiotic-

resistant, nosocomial pathogens compared with patients having community-acquired infection.

associated with translocation of organisms across the diaphragm or proximal small bowel. The most

prevalent organisms include S. pneumoniae, E. coli, and Klebsiella spp.

Secondary peritonitis is typically polymicrobial related to the origin of GI tract leakage.