Definition

Acute inflammation of the appendix sometimes followed by ischemia and perforation.

Classification based on complexity:

• Uncomplicated (>70% of cases): No involvement of the peritoneal cavity and no abscess
• Complicated: Involvement of the peritoneal cavity and/or presence of an abscess

Classification based on severity:

• Mild: Not critically ill with no signs of sepsis or septic shock

• Severe: Critically ill with signs of sepsis or septic shock

Most Likely Pathogens

Bacteria:
• Enterobacterales (mostly Escherichia coli including multidrug- resistant strains)
• Streptococcus spp. (e.g. of the S. anginosus group)
• Enterococcus spp.
• Anaerobes (mostly Bacteroides spp.)

Fungi (consider if recent course of antibiotics):

• Mostly Candida albicans

Parasites (consider in endemic settings):
• Enterobius vermicularis (pinworm) can contribute by causing obstruction of the appendix

Clinical Presentation

Acute abdominal pain (usually located in the right lower quadrant or migrating from the periumbilical area to the right lower quadrant), with nausea and vomiting; fever (≥ 38.0 °C) may be absent.

Important:

• Consider peritonitis if there is severe pain, diffuse rebound tenderness upon sudden release of pressure on the abdomen and abdominal muscular tensing

• Hypotension and signs of organ hypoperfusion (e.g. reduced urine output) are potential signs of sepsis /septic shock that need urgent treatment

Microbiology Tests

Mild uncomplicated cases: • Not usually needed

Severe cases:
• Blood cultures (ideally before starting antibiotics)
• Microscopy and culture of abscess øuid material (taken at the time of surgery) is not routinely recommended, but may be considered in speciöc cases to adjust empiric antibiotic treatment.

Other Laboratory Tests

Identify an alternative cause of abdominal pain:
• Urinalysis (dipstick or microscopy) to exclude an infection of the urinary tract
• Pregnancy test in women: to exclude an ectopic pregnancy

Determine disease severity and help identify a bacterial infection: White blood cell count, C-reactive protein and/or procalcitonin.

If sepsis is suspected consider additional laboratory tests.

Imaging

• Abdominal ultrasound to conörm the diagnosis

• Consider doing a CT scan of the abdomen if complications suspected or diagnosis uncertain

Treatment

Antibiotic Treatment Duration

Antibiotic treatment complementary to surgery

• Uncomplicated cases: Antibiotics can be stopped once appendix is removed

• Complicated cases: Antibiotics can be continued for a total of 5 days provided that symptoms resolved and the source of infection was eliminated with surgery

Treatment with antibiotics alone: 7 days

• Consider in selected cases if close clinical monitoring is feasible and considering patient preference (avoiding risks associated with surgery versus higher risk of recurrences and later need for surgery – about 30-40% over 5 years)

Mild cases

All dosages are for normal renal function

Antibiotics are listed in alphabetical order and should be considered equal treatment options unless otherwise indicated

First Choice

Second Choice

Metronidazole has excellent oral bioavailability and the IV route should be reserved for patients with impaired gastrointestinal function

Severe Cases

All dosages are for normal renal function

Antibiotics are listed in alphabetical order and should be considered equal treatment options unless otherwise indicated

First Choice

Second Choice

Consider meropenem only in complicated cases if there is a high risk of infection with ESBL-producing Enterobacterales

Clinical Considerations

• Appendectomy remains the main approach to eliminate the source of infection

• Empiric antibiotic treatment should be guided by: The severity of symptoms, considering local prevalence of resistance (particularly of isolates of Enterobacterales producing ESBL) and individual risk factors for resistant pathogens

Important:

• Simplify empiric treatment to a more narrow- spectrum antibiotic based on culture results or rapid clinical improvement if culture results unavailable

• Step down to oral treatment is based on improvement of symptoms, signs of infection and the ability to take oral antibiotics

• If signs and symptoms persist, abdominal imaging is suggested, or an alternative extra-abdominal source of infection should be considered

References

Web Annex. Infographics. In: The WHO AWaRe (Access, Watch, Reserve) antibiotic book. Geneva: World Health Organization; 2022 (WHO/MHP/HPS/EML/2022.02). Licence: CC BY-NC-SA 3.0 IGO.