What is the recommended diagnostic workup and management of acute diverticulitis, including criteria for outpatient treatment, appropriate antibiotic regimens, dietary recommendations, and indications for hospitalization or surgery?

Acute Diverticulitis Management

Diagnostic Workup

CT abdomen and pelvis with IV contrast is the gold standard imaging modality for suspected acute diverticulitis, with 98-99% sensitivity and 99-100% specificity. 1, 2

• CT confirms the diagnosis, differentiates uncomplicated from complicated disease, and identifies alternative diagnoses in patients presenting with left lower quadrant pain 1
• Imaging may be deferred only in patients with typical symptoms, prior documented diverticulitis with similar presentation, and no concerning features 1
• However, there is a strong trend toward routine CT imaging because clinical misdiagnosis occurs in 34-68% of cases, and early CT reduces hospital admissions by >50% and shortens length of stay 1, 3
• Ultrasound can be considered when CT is unavailable, and MRI when ultrasound is inconclusive, though MRI has insufficient evidence for routine use 1

Laboratory testing should include complete blood count and C-reactive protein to assess disease severity and risk stratification. 1, 2

---

Classification: Uncomplicated vs. Complicated

Uncomplicated diverticulitis = localized colonic inflammation with diverticula, without abscess, phlegmon, fistula, obstruction, bleeding, or perforation 1, 3

Complicated diverticulitis = inflammation with any of the above features 1, 3

Approximately 85-88% of cases are uncomplicated 3, 2

---

Outpatient vs. Hospitalization Criteria

Most patients with uncomplicated diverticulitis should be managed as outpatients 1, 3

Outpatient eligibility requires ALL of the following:

• Ability to tolerate oral fluids and medications 1, 3
• Temperature <100.4°F (38°C) 3
• Pain controlled with acetaminophen alone (pain score <4/10) 3
• No significant comorbidities or frailty (cirrhosis, chronic kidney disease, heart failure, poorly controlled diabetes) 1, 3
• Adequate home and social support 1
• Immunocompetent status 1, 3
• No signs of systemic inflammatory response or sepsis 1, 3

Outpatient management saves 35-83% in costs per episode compared to hospitalization, with only 4.3% failure rate requiring subsequent admission. 1, 3, 4

Hospitalization is required for:

• Complicated diverticulitis (abscess, perforation, obstruction, fistula) 1, 3
• Inability to tolerate oral intake 1, 3
• Severe pain or systemic symptoms (fever, sepsis) 1, 3
• Immunocompromised status (chemotherapy, high-dose steroids, organ transplant) 1, 3, 2
• Significant comorbidities or frailty 1, 3
• Age >80 years (lower threshold for admission) 3, 2
• Pregnancy 3, 2

---

Antibiotic Management

For Uncomplicated Diverticulitis: Selective Use Only

Most immunocompetent patients with uncomplicated diverticulitis do NOT require antibiotics—observation with supportive care is first-line therapy. 1, 3, 5, 2

This recommendation is based on multiple high-quality RCTs (including DIABOLO trial with 528 patients) showing antibiotics do not accelerate recovery, prevent complications, or reduce recurrence 3, 5

Reserve antibiotics for patients with ANY of these high-risk features:

Clinical indicators:

• Persistent fever (>100.4°F) or chills despite supportive care 3, 2
• Refractory symptoms or vomiting 1, 3, 2
• Inability to maintain oral hydration 1, 3
• Symptom duration >5 days before presentation 1, 3

Laboratory markers:

• C-reactive protein >140 mg/L 1, 3, 2
• White blood cell count >15 × 10⁹/L or increasing leukocytosis 1, 3, 2

CT findings:

• Fluid collection or abscess 1, 3
• Longer segment of colonic inflammation 1, 3
• Pericolic extraluminal air 1, 3

Patient factors:

• Immunocompromised status (chemotherapy, high-dose steroids, organ transplant) 1, 3, 2
• Age >80 years 3, 2
• Pregnancy 3, 2
• ASA physical status III or IV 1, 3
• Significant comorbidities (cirrhosis, CKD, heart failure, poorly controlled diabetes) 3, 2

Antibiotic Regimens When Indicated

Outpatient oral therapy (4-7 days for immunocompetent patients):

• First-line: Amoxicillin-clavulanate 875/125 mg PO twice daily 3, 2
• Alternative: Ciprofloxacin 500 mg PO twice daily PLUS Metronidazole 500 mg PO three times daily 3, 2

Inpatient IV therapy (transition to oral within 48 hours when tolerated):

• Ceftriaxone PLUS Metronidazole 3, 2
• Piperacillin-tazobactam 3, 2
• Ampicillin-sulbactam 2

Duration:

• Immunocompetent patients: 4-7 days total 3, 2
• Immunocompromised patients: 10-14 days total 3
• Post-drainage of abscess: 4 days after adequate source control 3

---

Dietary Recommendations

During acute phase: Clear liquid diet for patient comfort, advancing as symptoms improve 3, 2

Long-term prevention (after resolution):

• High-fiber diet (≥22.1 g/day from fruits, vegetables, whole grains, legumes) 3
• Low intake of red meat and sweets 3
• Do NOT restrict nuts, corn, popcorn, or small-seeded fruits—these are NOT associated with increased diverticulitis risk 3

---

Management of Complicated Diverticulitis

Small abscess (<4-5 cm):

• IV antibiotics alone for 7 days 3

Large abscess (≥4-5 cm):

• CT-guided percutaneous drainage PLUS IV antibiotics 3
• Continue antibiotics for 4 days after adequate source control in immunocompetent patients 3

Generalized peritonitis or sepsis:

• Emergent surgical consultation 3, 2
• IV antibiotics (ceftriaxone + metronidazole or piperacillin-tazobactam) 3, 2
• Surgical options: Hartmann's procedure or primary resection with anastomosis 3, 6
• Mortality: 0.5% for elective resection vs. 10.6% for emergent resection 2

---

Follow-Up Protocol

Mandatory re-evaluation within 7 days of diagnosis (or sooner if symptoms worsen). 3, 7

Colonoscopy 6-8 weeks after symptom resolution is recommended for:

• First episode of uncomplicated diverticulitis (if no recent high-quality colonoscopy) 3
• Any complicated diverticulitis (7.9% associated cancer risk) 3
• Patients >50 years requiring routine screening 3
• Presence of alarm features (rectal bleeding, weight loss, change in stool caliber, iron-deficiency anemia) 3

---

Surgical Considerations for Recurrent Disease

Elective sigmoidectomy should NOT be based on number of episodes alone. 3

Consider surgical referral when:

• ≥3 episodes within 2 years 3
• Persistent symptoms >3 months (smoldering diverticulitis) 3
• Significant quality of life impairment 3
• History of complicated diverticulitis 3
• Immunocompromised status 3

The DIRECT trial showed significantly better quality of life at 6 months and 5 years after elective surgery vs. conservative management 3

---

Prevention of Recurrence

• Regular vigorous physical activity 3
• Maintain BMI 18-25 kg/m² 3
• Smoking cessation 3
• Avoid nonaspirin NSAIDs when possible 3
• Do NOT prescribe mesalamine or rifaximin—high-certainty evidence shows no benefit but increased adverse events 3

---

Critical Pitfalls to Avoid

• Do NOT routinely prescribe antibiotics for uncomplicated diverticulitis without high-risk features—this contributes to antibiotic resistance without clinical benefit 3, 5
• Do NOT assume all patients require hospitalization—most can be safely managed outpatient with proper follow-up 1, 3, 4
• Do NOT withhold antibiotics from immunocompromised patients, those with sepsis, or those with complicated disease 3, 2
• Do NOT apply the "no antibiotics" approach to Hinchey 1b or higher disease—evidence excluded these patients 3
• Do NOT delay surgical consultation in patients with frequent recurrences significantly affecting quality of life 3