What is diverticulitis and how is it treated?

What is Diverticulitis and How to Treat It

Definition and Pathophysiology

Diverticulitis is inflammation of colonic diverticula (outpouchings from the intestinal wall), most commonly affecting the sigmoid colon in Western populations. 1, 2 The condition occurs when these diverticula become infected or inflamed, though the exact mechanism remains incompletely understood. 3

Diverticulitis affects approximately 180 per 100,000 people annually in the United States, resulting in 200,000 hospital admissions and over $6.3 billion in healthcare costs per year. 4 Of patients with diverticulosis (the presence of diverticula), only 1-4% will develop acute diverticulitis in their lifetime. 4

Clinical Presentation

Patients typically present with left lower quadrant abdominal pain accompanied by fever, nausea, vomiting, and leukocytosis. 4 However, symptoms can be non-specific, and elderly patients or those on corticosteroids may have minimal physical findings even with severe disease. 5 Other symptoms include anorexia, constipation, diarrhea, and dysuria. 6

Diagnostic Approach

Contrast-enhanced CT of the abdomen and pelvis is the gold standard diagnostic test, with 98-99% sensitivity and 99-100% specificity. 2, 4 CT is essential because clinical assessment alone misclassifies 34-68% of suspected cases. 2 The imaging confirms the diagnosis, distinguishes uncomplicated from complicated disease, and identifies alternative diagnoses. 2, 5

Initial laboratory studies should include complete blood count, basic metabolic panel, C-reactive protein, and urinalysis. 6, 2

Disease Classification

Uncomplicated Diverticulitis (85-88% of cases)

Localized inflammation without abscess, perforation, fistula, obstruction, or bleeding. 2, 4

Complicated Diverticulitis (12-15% of cases)

Presence of abscess, perforation, fistula, stricture, obstruction, or bleeding. 2, 4

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Treatment Algorithm

Step 1: Determine Disease Severity and Patient Risk

Most immunocompetent patients with uncomplicated diverticulitis do NOT require antibiotics—observation with supportive care is first-line therapy. 2, 4 This recommendation is based on high-quality randomized trials, including the DIABOLO trial (528 patients), which demonstrated that antibiotics neither accelerate recovery nor prevent complications or recurrence. 2

Criteria for Outpatient Management (All Must Be Met):

• CT-confirmed uncomplicated disease 2
• Ability to tolerate oral fluids and medications 2, 4
• Temperature <100.4°F 2
• Pain controlled with acetaminophen alone (score <4/10) 2
• No significant comorbidities or frailty 2, 4
• Immunocompetent status 2, 4
• Adequate home support with reliable follow-up within 7 days 2

Outpatient management achieves 35-83% cost savings without compromising safety. 2

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Step 2: Identify High-Risk Features Requiring Antibiotics

Reserve antibiotics for patients with ANY of the following:

Clinical Indicators:

• Persistent fever or chills despite supportive care 2
• Refractory symptoms or vomiting 2, 4
• Inability to maintain oral hydration 2, 4
• Symptom duration >5 days before presentation 2

Laboratory Markers:

• C-reactive protein >140 mg/L 2, 4
• White blood cell count >15 × 10⁹/L or rising leukocytosis 2, 4

CT Findings:

• Fluid collection or abscess 2, 4
• Longer segment of inflammation 2
• Pericolic extraluminal air 2

Patient Factors:

• Immunocompromised status (chemotherapy, high-dose steroids, organ transplant) 2, 4
• Age >80 years 2, 4
• Pregnancy 2, 4
• Significant comorbidities (cirrhosis, chronic kidney disease, heart failure, poorly controlled diabetes) 2, 4
• ASA physical status III-IV 2

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Step 3: Select Appropriate Antibiotic Regimen

Outpatient Oral Therapy (4-7 days for immunocompetent patients):

• First-line: Amoxicillin-clavulanate 875/125 mg PO twice daily 2, 4
• Alternative: Ciprofloxacin 500 mg PO twice daily PLUS Metronidazole 500 mg PO three times daily 2, 4

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

• Ceftriaxone PLUS Metronidazole 2, 4
• Piperacillin-tazobactam 2, 4
• Ampicillin-sulbactam 4

Duration:

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

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Step 4: Manage Complicated Diverticulitis

Small Abscess (<4-5 cm):

IV antibiotics alone for 7 days 2

Large Abscess (≥4-5 cm):

CT-guided percutaneous drainage PLUS IV antibiotics; continue antibiotics for 4 days post-drainage in immunocompetent patients 2, 4

Generalized Peritonitis or Sepsis:

• Emergent surgical consultation for source control (Hartmann procedure or primary resection with anastomosis) 2, 4
• Immediate broad-spectrum IV antibiotics 2, 4

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Step 5: Supportive Care for All Patients

• Clear liquid diet during acute phase, advancing as symptoms improve 2
• Acetaminophen for pain control (avoid NSAIDs) 2, 4
• Adequate oral hydration 2

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Follow-Up and Prevention

Immediate Follow-Up:

Mandatory re-evaluation within 7 days (or sooner if symptoms worsen). 2 Patients should return immediately for fever >101°F, severe uncontrolled pain, persistent vomiting, inability to eat/drink, or signs of dehydration. 2

Colonoscopy:

Perform colonoscopy 6-8 weeks after symptom resolution for patients with complicated diverticulitis (7.9% cancer risk), first episode of uncomplicated diverticulitis, or those >50 years requiring routine screening. 2, 6

Recurrence Prevention:

• High-fiber diet (≥22.1 g/day from fruits, vegetables, whole grains, legumes) with low red meat and sweets 2, 7
• Regular vigorous physical activity 2, 7
• Maintain normal BMI (18-25 kg/m²) 2, 7
• Smoking cessation 2, 7
• Avoid chronic NSAID and opioid use 7, 4
• Do NOT restrict nuts, corn, popcorn, or small-seeded fruits—this outdated advice is not evidence-based 2, 7

Do NOT prescribe mesalamine or rifaximin for prevention—these have no proven benefit and may cause adverse events. 2, 7

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Critical Pitfalls to Avoid

• Do NOT routinely prescribe antibiotics for uncomplicated diverticulitis without high-risk features—this contributes to antimicrobial resistance without clinical benefit 2
• Do NOT assume all patients require hospitalization—most immunocompetent patients with uncomplicated disease can be safely managed outpatient 2
• Do NOT withhold antibiotics from immunocompromised patients—they require immediate 10-14 day therapy, lower threshold for repeat imaging, and early surgical consultation 2, 4
• Do NOT apply the "no antibiotics" approach to complicated diverticulitis (Hinchey 1b or higher)—the evidence specifically excluded these patients 2
• Do NOT delay surgical consultation in patients with generalized peritonitis, sepsis, or failed medical management after 5-7 days 2

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Special Populations

Immunocompromised Patients:

Require immediate antibiotic therapy for 10-14 days, lower threshold for CT imaging and surgical consultation, and may present with milder signs despite severe disease. 2, 4 Corticosteroid use specifically increases perforation and mortality risk. 2

Elderly Patients (>65 years):

Require lower threshold for antibiotic treatment and closer monitoring, even with localized disease. 2 They may have limited physical findings despite severe diverticulitis. 5

Pregnant Patients:

Require antibiotics regardless of other factors. 2, 4