Infective Colitis in Adults - Treatment

Overview of Aetiology

Step 1: Initial Assessment

• Assess dehydration severity (skin turgor, mucous membranes, urine output)
• Identify "red flag" features: high fever (≥38.5°C), bloody/mucoid stool, severe abdominal pain, immunocompromised state, toxic appearance
• Differentiate invasive (fever, dysentery, tenesmus, bloody stool) vs. noninvasive (watery, afebrile, self-limited) disease

• FBC, U&E, inflammatory markers (CRP, ESR), LFTs, albumin, ABG
• Stool MCS, C. difficile antigen + toxin, multiplex PCR for stool pathogens
• Blood cultures if systemic illness suspected
• HIV testing if risk factors present

Step 2: Fluid Resuscitation (Universal First Step)

• Mild-moderate dehydration: Oral rehydration solution (ORS) - equally effective as IV in alert patients; adults may need 1000 mL/hour
• Severe dehydration: IV lactated Ringer's or normal saline + KCl + bicarbonate as needed; hospitalize
• Reduced-osmolarity ORS (Na⁺ 75 mmol/L, osmolarity 245 mmol/L) is better tolerated but avoid in high-volume diarrhea (risk of hyponatremia)

Step 3: Pathogen-Directed Antimicrobial Treatment

Antimotility Agents

• Bismuth subsalicylate (525 mg q30-60 min, up to 5 doses/day, repeat day 2): safe and effective in bacterial infectious diarrhea
• Loperamide: safe in non-dysenteric, afebrile, watery diarrhea - AVOID in true dysentery (fever + blood/pus in stool) as it worsens invasive infection
• Opiates/anticholinergics: NOT recommended in invasive bacterial colitis

Empirical Antibiotic Indications

• Patient appears toxic, high fever, dysentery
• Severe traveler's diarrhea
• Suspected C. difficile colitis
• Immunocompromised state
• Known outbreak organism isolated

Pathogen-Specific Treatment

Campylobacter jejuni (most common bacterial cause in developed countries)

• First line: Azithromycin 500 mg PO daily x 3 days, or Erythromycin 500 mg PO BD x 5 days
• Second line: Ciprofloxacin 500 mg PO BD x 7 days (note: ~20% US resistance; >80% resistance in SE Asia - use only if susceptibility confirmed)
• Antimotility agents contraindicated unless given with antibiotics (invasive enteritis)
• ROSEN's Emergency Medicine, p. 1305

Salmonella (non-typhoidal)

• Most cases are self-limiting and do not require antibiotics (2-5 day illness)
• Antibiotic indications: Bacteremia, extremes of age, immunocompromise, sickle cell disease, severe systemic illness
• Treatment when indicated: Fluoroquinolone (ciprofloxacin 500 mg PO BD x 5-7 days) OR azithromycin OR ceftriaxone (for resistant strains)
• Caution: STEC (E. coli O157:H7) - antibiotics are NOT recommended (may increase HUS risk up to 17-fold)

Shigella (bacillary dysentery)

• Treatment shortens illness and eradicates the pathogen from stool within 48 hours
• When to treat: Not improving, immunocompromised, S. dysenteriae (treat even if asymptomatic - outbreak prevention)
• Antibiotics: Azithromycin (500 mg day 1, then 250 mg x 4 days) - preferred due to widespread fluoroquinolone resistance; or ciprofloxacin 500 mg BD x 3 days if susceptible; trimethoprim-sulfamethoxazole as second line
• Fluoroquinolone-resistant Shigella is increasingly common worldwide

Traveler's Diarrhea

• Ciprofloxacin 500 mg PO BD x 3 days (empirical first line)
• Rifaximin 200 mg TDS or 400 mg BD x 3 days (for non-invasive traveler's diarrhea, Mexico/SE Asia - not effective against Campylobacter/Shigella)
• Azithromycin for resistant strains or suspected Campylobacter

Clostridioides difficile Infection (CDI)

• Without ileus: Vancomycin 500 mg QID PO/NGT + IV Metronidazole 500 mg q8h
• With ileus: Add rectal vancomycin every 6 hours

• Switch to the other first-line agent (vancomycin if fidaxomicin used initially, or vice versa)
• Consider pulse-and-taper vancomycin regimen
• High recurrence risk: Bezlotoxumab 10 mg/kg IV stat (monoclonal antibody vs toxin B)
• Multiple recurrences: Fecal microbiota transplantation (FMT) - 90% resolution vs 30% with vancomycin alone

CMV Colitis (immunocompromised patients)

• Severe/tissue-invasive disease: IV Ganciclovir 5 mg/kg BD until clinical improvement (~7 days) then oral Valganciclovir 900 mg OD x 14 days
• Mild-moderate disease: Oral Valganciclovir 450 mg BD
• Monitor viral load and antigen weekly; continue until symptoms and viremia resolve
• Generally continue existing immunosuppression

Amoebic Colitis (Entamoeba histolytica)

• Mild-moderate disease: Oral Metronidazole x 10 days (all patients, including asymptomatic carriers)
• Fulminant colitis/peritonitis/toxic megacolon: IV Metronidazole + IV Ceftriaxone (for gram-negative cover)
• Follow with luminal agent (paromomycin or diloxanide furoate) to eliminate cysts

Strongyloides Colitis

• Ivermectin 200 mcg/kg/day x 2 days (drug of choice)
• Warning: Strongyloides hyperinfection syndrome is a catastrophic complication in patients treated with steroids/immunosuppression - screen before starting steroids in endemic areas (mortality 77-100%)

Step 4: Hospitalization Criteria

• Toxic appearance
• Severe or persistent symptoms
• Unable to tolerate oral fluids
• Significant electrolyte abnormalities / severe dehydration
• Extremes of age or immunocompromised
• Suspected fulminant CDI or toxic megacolon

Surgical Treatment (CDI - Fulminant)

• Abdominal compartment syndrome
• Hemodynamic instability with ongoing vasopressor requirement
• Worsening end-organ failure (especially renal)
• Need for mechanical ventilation

Treatment Algorithm

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