Infectious Diseases I

Esophageal, gastric, and duodenal secretions are usually sterile or with limited inocula of gram-

positive bacteria and Candida spp.

Proximal small bowel is densely populated with aerobic gram-negative bacilli including E. coli,

Klebsiella spp., Proteus spp., and Enterobacter spp., as well as populations of aerobic gram-positive

bacteria such as S. aureus, streptococci, and enterococci.

The distal small bowel and the large bowel are populated with proximal small bowel flora in

addition to anaerobic gram-negative and gram-positive organisms, including Bacteroides fragilis

and Clostridioides spp. (usually non–C. difficile).

Tertiary peritonitis includes core organisms of primary and secondary peritonitis further compounded by

the influence of management strategies, including malnutrition, anatomic disruption, and antimicrobial

therapy.

The diagnosis of complicated intra-abdominal infection relies on assessment of clinical signs and

symptoms, differentiation from other causes of infection, and radiographic evaluation.

are the most common presenting signs and symptoms. Additional symptoms of anorexia, abdominal

distention, nausea, or vomiting, with or without fever, tachycardia, or tachypnea. These are often

difficult to assess in critically ill patients; therefore, intra-abdominal infection should be considered in

patients with unexplained new-onset organ dysfunction and sepsis.

Radiographic evaluation is commonly performed using abdominal radiographs, ultrasonography, and

CT, including contrast CT to assess for vascular thrombosis. Contrast studies of postoperative drains or

fistulae may also help assess anastomotic integrity.

Culture of intra-abdominal fluid (e.g., ascitic fluid in patients with cirrhosis; intraoperative culture

of abscess fluid) associated with the primary source should be obtained in moderately to severely ill

patients. Gram stain results should be used to help guide empiric antimicrobial therapy. Pathogens

identified on final culture should guide definitive antimicrobial therapy.

Resuscitation for hemodynamic instability should be initiated and managed according to the Surviving

Sepsis Campaign guidelines.

resection is recommended for patients with diffuse peritonitis. Patients with focal peritonitis should

undergo percutaneous abscess and fluid drainage.

Empiric antimicrobial therapy should be initiated in patients thought to have complicated intra-

abdominal infections.

Empiric antimicrobial regimens should be based on the source/location of intra-abdominal

infection, community-acquired or health care–associated disposition of infection, severity of

infection, local pathogen trends and susceptibilities, MDRO risk factors (e.g., hospitalization for

greater than 48 hours during current admission or in the previous 90 days; recent broad-spectrum

antimicrobial therapy; infection developing greater than 48 hours after initial source control; home

wound care or dialysis within preceding 90 days), and patient-specific colonization patterns.

Individual antimicrobial agents should be dosed according to available pharmacokinetic and

pharmacodynamic principles to optimize efficacy and limit toxicity.