Intra-abdominal infections

Question 1

Primary Peritonitis

Answer 1

Peritoneal dialysis related peritonitis

Spontaneous bacterial peritonitis

Question 2

Secondary Peritonitis

Answer 2

Diverticulitis (+/- perforation/abscess)

Appendicitis (+/- rupture)

Cholecystitis

Intra-abdominal abscess

Cholangitis

Necrotizing pancreatitis

Question 3

Uncomplicated infection

Answer 3

Confined within visceral structure (gall bladder, liver, spleen, kidneys)

Does not extend into peritoneum

Question 4

Complicated infection

Answer 4

Extends beyond a single organ into the peritoneal space and associated with peritonitis

Question 5

Community-acquired infection

Answer 5

Occurs within 48 hours of hospital admission, no healthcare exposure

Caused by normal intra-abdominal flora

Question 6

Healthcare-associated infection

Answer 6

Occurs after 48 hours of admission

Healthcare exposure in last 12 months

Question 7

Spontaneous Bacterial Peritonitis (SBP)

Answer 7

No obvious source of bacterial contamination

Patients at high risk:
- Hepatic failure and ascites–alcoholic cirrhosis
- Continuous ambulatory peritoneal dialysis (CAPD)

Question 8

SBP common pathogens

Answer 8

E. coli and other Enterobacterales (e.g., K. pneumoniae)

Streptococci

Enterococci

Staphylococcus aureus and coagulase negative staphylococci (more common with CAPD)

Question 9

SBP Presentation

Answer 9

Abdominal pain

Nausea, vomiting, diarrhea

Fevers, chills

Reduced/absent bowel sounds

Altered mental status/encephalopathy

Question 10

SBP Diagnosis

Answer 10

Signs and symptoms of infection

Ascitic fluid analysis
⎻ Low ascitic fluid protein (< 2.5 g/dL)
⎻ Absolute neutrophil count > 250/mm3

Question 11

SBP Empiric therapy

Answer 11

Ceftriaxone 1-2 g IV q24h
Cefepime 1 g IV q8h
Zosyn 3.375 g IV q6-8h
Meropenem 1 g IV q8h

MRSA risk: Vancomycin, linezolid, daptomycin

Anaerobic coverage: Beta-lactam/beta-lactamase inhibitor, carbapenem, add metronidazole

Transition to oral therapy appropriate once clinically stable

Question 12

SBP Treatment duration

Answer 12

Patients with cirrhosis and ascites:
- 5-7 days
- Secondary prophylaxis recommended after treatment completed: Bactrim DS PO daily or ciprofloxacin 500 mg PO daily

Peritonitis in patients undergoing CAPD
- May require removal of peritoneal dialysis catheter and transition to hemodialysis
- Intraperitoneal administration of antibiotics preferred
- 14-21 days

Question 13

Intra-abdominal infection common pathogens

Answer 13

E. coli, klebsiella, enterobacter, proteus

Streptococcus, enterococcus

Bacteroides (B. fragilis), clostridium, prevotella, peptostreptococcus

Candida

Polymicrobial!!

Question 14

What makes intra-abdominal infections unique?

Answer 14

Multiple organ systems affected
▪GI tract – bowel paralysis → abdominal distention
▪Cardiovascular – fluid shifts → hypotension, tachycardia, vasoconstriction
▪Respiratory – hypoxemia
▪Renal – decreased renal perfusion → renal failure

Bacterial synergy
- Enterobacterales (e.g., E. coli) create optimal environment for anaerobic bacteria
- Anaerobes cause abscess formation and have several virulence factors

Question 15

Intra-abdominal infections presentation

Answer 15

Abdominal pain and distention
Nausea and vomiting
Fever +/- chills
Loss of appetite
Inability to pass flatus and/or feces

Physical exam findings/vital signs
▪Tachypnea, tachycardia
▪Hypotension
▪Significant abdominal tenderness
▪Rigidity of abdominal wall
▪Reduced or absent bowel sounds

Question 16

Intra-abdominal infections diagnostic work-up

Answer 16

Signs and symptoms of IAI + Imaging (CT scan, X-ray)

Question 17

Intra-abdominal infection treatment consideration

Answer 17

Source control!!!

Antimicrobial therapy

Question 18

Examples of source control procedures

Answer 18

Repair perforations
Resection of infected organs/tissue
Removal of foreign material
Drain purulent collections

Important to obtain cultures

Question 19

Steps for selecting empiric therapy

Answer 19

1. Select agent or combination with high likelihood to cover common organisms
   - agents not recommended if resistance exceeds 10-20%
2. Consider if enterococci coverage is necessary
   - recommended for high severity IAI, history of recent cephalosporin use, immunocompromised, biliary source of infection, history of valvular heart disease, and/or prosthetic intravascular material
3. Consider if anti-fungal coverage is necessary
   - empiric anti-fungal coverage is unnecessary: only if isolated culture

Question 20

IAI Community-acquired mild-moderate severity

Answer 20

Ceftriaxone + Metronidazole
Cefepime + Metronidazole
Cefoxitin
Ertapenem
Tigecycline

Question 21

IAI Community-acquired high severity and healthcare associated

Answer 21

Zosyn
Meropenem
Cefepime + Metronidazole

Question 22

AMPICILLIN/SULBACTAM IS NOT RECOMMENDED DUE TO E.COLI RESISTANCE

Answer 22

AMPICILLIN/SULBACTAM IS NOT RECOMMENDED DUE TO E.COLI RESISTANCE

Question 23

Pathogen-Directed regimens

Answer 23

Acceptable to de-escalate the empiric antibiotic regimen once culture results are available

Anaerobic bacteria is more difficult to isolate in culture

Common to maintain anaerobic coverage even if culture does not isolate anaerobic bacteria

Question 24

Oral antibiotic regimens

Answer 24

Transition when clinically stable

Augmentin
Cefpodoxime + Metronidazole
Cephalexin + Metronidazole
Cefadroxil + Metronidazole
Ciprofloxacin + Metronidazole
Levofloxacin + Metronidazole
Bactrim + Metronidazole

Question 25

IAI Treatment duration

Answer 25

General duration: 4-7 days after source control Diverticulitis: - uncomplicated: antibiotic not needed - moderate/severe: 5-10 days Appendicitis without perforation, abscess, or peritonitis: 24 hours after surgery Cholecystitis without perforation: 24 hours after surgery Bowel injuries repaired within 12 hours: 24 hours after surgery