Intra-abdominal infections (IAI) occur due to disruption of the normal anatomic barrier.
In the hollow viscera is where common disruptions occur, which allows intraluminal bacteria to invade and proliferate in the usually sterile area (ie peritoneal cavity or retroperitoneum).
Community-acquired intra-abdominal infection is usually secondary to gastroduodenal perforation, ascending cholangitis, cholecystitis, appendicitis, colon diverticulitis with or without perforation, or pancreatitis.
Uncomplicated IAI infectious process involves only a single organ and does not extend to the peritoneum.
Complicated IAI is when infection extends beyond the hollow viscus of origin into the peritoneal space and may be associated with peritonitis or abscess formation.


  • Routine history, physical & laboratory exams usually identify patients w/ suspected intra-abdominal infections (IAI)


Community-acquired Intra-abdominal Infections (CA-IAI)

  • Usually secondary to gastroduodenal perforation, ascending cholangitis, cholecystitis, appendicitis, colon diverticulitis w/ or w/o perforation, or pancreatitis
  • Common pathogens involved are Enterobacteriaceae, Streptococcus spp, & anaerobes (especially Bacteroides fragilis)

Healthcare-associated Intra-abdominal Infections (HA-IAI)

  • Usually secondary to leak or perforations from anastomosis or abscess from surgical site &/or wound infections
  • Considered in the development or worsening of organ dysfunction in the days after abdominal surgery
  • Range of pathogen involved is broader, which includes Enterobacteriaceae, Streptococcus spp, anaerobes, Enterococcus spp, Candida spp, or Pseudomonas aeruginosa
  • Commonly involves at least 1 multidrug-resistant (MDR) organism, which needs the use of broad-spectrum antibiotics that is based on culture results & local antibiograms
  • Community-onset HA-IAI includes patients w/ history of surgery, hospitalization, dialysis, or stayed in a care facility for a long time w/in the previous 12 months before the culture date
  • Hospital-onset HA-IAI includes patients w/ a positive culture result obtained >48 hours after hospital admission

Uncomplicated Intra-abdominal Infections (IAI)

  • Infectious process involves only a single organ & does not extend to the peritoneum
    • Usually involves intramural inflammation of the gastrointestinal tract
  • May progress to complicated infection if not properly treated
  • Usually has low severity but may present as severe sepsis

Complicated Intra-abdominal Infections (IAI)

  • Infection that extends beyond the hollow viscus of origin into the peritoneal space & may be associated w/ peritonitis or abscess formation


  • May provide the basis of decision regarding the need for intensive resuscitation or rehydration, need for diagnostic imaging procedures, timing of antibiotic therapy, & urgent need for an intervention
    • Patient w/ intra-abdominal infections (IAI) usually presents w/ rapid onset of abdominal pain, loss of appetite, nausea, vomiting, bloating or obstipation,that may be accompanied w/ signs of inflammation (eg pain, tenderness, fever, tachycardia, tachypnea)
    • Hypotension & hypoperfusion signs indicate progress to severe sepsis
    • Abdominal rigidity is suggestive of peritonitis & need for urgent surgical intervention
  • IAI should be considered in patients who have unreliable physical exam findings (eg patients w/ obtunded mental status, spinal cord injury, or who are immunosuppressed) & have evidence of undetermined infection

Laboratory Tests

Gram Stain

  • Helpful in patients w/ healthcare-associated intra-abdominal infections (IAI) to determine co-infection w/ yeast
  • Not recommended in patients w/ community-acquired IAI

Blood Culture

  • Helpful in determining the length of therapy in immunocompromised or clinically toxic-appearing patients
  • Blood cultures & peritoneal fluid direct examination for yeasts must be done in patients w/ healthcare-associated (HA)-IAI & community-acquired (CA)-IAI who are immunosuppressed &/or in septic shock
  • Considered significant if the microbes isolated have established pathogenic potential or are present in ≥2 blood cultures

Aerobic or Anaerobic Culture from Site of Infection

  • Specimens that will be collected from the site of infection should be at least 1 mL of fluid or tissue & is transported to the lab in an appropriate transport system
    • Regardless if it is a community-acquired or nosocomial peritonitis, samples from close suction drains & drainage systems should not be used as these yield uninterpretable results
  • Considered significant if the microbes isolated are in moderate or heavy concentrations
  • Recommended in patients w/ HA-IAI, perforated appendicitis, other CA-IAI if the common community isolates (eg Escherichia coli) have 10-20% resistance to the widely used local antimicrobial regimen, & in patients who are at high risk especially those w/ prior antibiotic use
  • Optional in patients w/ CA-IAI
    • Determines changes in resistance patterns of pathogens associated w/ CA-IAI & guides follow-up oral therapy
  • Anaerobic cultures are not required for patients w/ CA-IAI if empiric antimicrobial therapy given has activity against anaerobic pathogens

Susceptibility Testing

  • Recommended for species which are more likely to yield resistance (eg Pseudomonas, Proteus, Acinetobacter, Staphylococcus aureus, & Enterobacteriaceae w/ moderate-heavy growth)

Fine-needle Aspiration

  • Image-guided, diagnostic, fine-needle aspiration can be performed for bacterial & fungal small (<3 cm) intra-abdominal collections & when diagnosis is in doubt


  • For pediatric patients, non-irradiating imaging is preferred
  • In patients w/ clear sign of diffuse peritonitis & in whom surgery is warranted, further diagnostic imaging is not recommended
    • Imaging may not also be required in a critically ill patient w/ a suspected peritonitis from a perforated organ if it would delay surgery
  • Plain X-ray of the abdomen is usually the 1st imaging procedure requested in patients suggestive of intra-abdominal infections (IAI)
    • Upright films may show free air under the diaphragm (most commonly on the right side), which indicates perforated viscus
  • Computed tomography (CT) scan is the imaging modality of choice in stable adult patients who will not undergo immediate laparotomy
    • Will determine the presence & source of IAI
    • Also done in stable patients in whom postoperative peritonitis is suspected
  • For unstable patients who do not need immediate laparotomy, abdominal ultrasound is the imaging procedure of choice
    • Patient’s discomfort, abdominal distension & bowel gas interference are the limitations of this test
    • 1st imaging test used in patients w/ suspected acute cholecystitis or cholangitis
  • Diagnostic peritoneal lavage may be used in complicated IAI when neither CT scan nor abdominal ultrasound is available
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