Treatment & Management of Dysentery

1. Bacillary Dysentery (Shigellosis)

When to Treat

• In high-income settings, uncomplicated watery diarrhea without fever may be self-limiting and may not require treatment.
• The WHO does not routinely recommend antibiotics for non-bloody, non-febrile diarrheal episodes.
• The CDC recommends limiting antibiotic treatment to patients who are immunocompromised, have severe illness requiring hospitalization, or have invasive disease/complications.

Antibiotic Therapy

• For S. dysenteriae type 1: treat for 5 days
• For immunocompromised patients: treat for 7-10 days
• Non-dysenteriae Shigella in immunocompetent: 3-day course is sufficient

• Ceftriaxone IV/IM: children 50-100 mg/kg once daily for 2-5 days; adults 1 g every 24 h for 3 days

• Source: Harrison's Principles of Internal Medicine 22E (Table 172-1); Goldman-Cecil Medicine (Fig. 285-1)

Resistance

• High rates of resistance to amoxicillin, ampicillin, tetracycline, and early-generation quinolones (e.g., nalidixic acid)
• Resistance is driven by plasmids, transposons, and chromosomal mutations in DNA gyrase/topoisomerase IV
• Empiric therapy should be guided by local susceptibility data whenever possible; adjust when individual culture results return

Supportive Care

• Oral rehydration therapy (ORT) is the cornerstone of supportive care
• Zinc supplementation: 20 mg daily (10 mg for infants ≤6 months) for 10-14 days - recommended in developing countries only
• Anti-motility agents (loperamide, opiates) should be avoided - they may prolong illness and worsen colitis
• Antipyretics for fever management

Complications to Monitor

2. Amoebic Dysentery (Entamoeba histolytica)

Treatment by Clinical Setting

• Source: Katzung's Basic and Clinical Pharmacology 16th Ed.

Key Drug Notes

• Metronidazole and tinidazole (nitroimidazoles) kill trophozoites but not cysts - a luminal agent is always required in combination to eradicate intestinal carriage
• Tinidazole has a better side-effect profile than metronidazole and simpler dosing
• Each luminal amebicide (diloxanide furoate, iodoquinol, paromomycin) eradicates carriage in ~80-90% of patients
• Tetracyclines and erythromycin are alternatives for moderate colitis but are not effective against extraintestinal disease

3. Trichuris Dysentery Syndrome

Quick Summary Table

• Harrison's Principles of Internal Medicine 22E (2025), pp. 1367-1368
• Goldman-Cecil Medicine, International Edition, pp. 3156-3157
• Katzung's Basic and Clinical Pharmacology 16th Ed., pp. 1445-1446

Blood with Mucus Diarrhea

Pathophysiology

• Mucosal invasion and destruction of the colonic epithelium
• Release of blood and mucus into the intestinal lumen
• Recruitment of neutrophils causing crypt abscesses and mucosal ulcerations
• Tenesmus (painful urge to defecate) results from rectal inflammation

Differential Diagnosis

Infectious Causes (Most Common - Acute Onset)

Key distinguishing feature: High fecal PMNs = bacterial invasion (Shigella, Campylobacter). Few PMNs + erythrophagocytic trophozoites = E. histolytica.

Non-Infectious Causes (Must Not Miss)

Clinical Clues to Narrow the Differential

Investigations

Stool Tests

• Stool culture: minimum panel includes Campylobacter, E. coli O157:H7, Salmonella, Shigella, and ideally Yersinia
• Shiga toxin immunoassay (in addition to, not instead of, O157:H7 culture)
• C. difficile toxin (PCR/EIA) - especially if antibiotic history
• Stool microscopy: fecal leukocytes (PMNs) - high in bacterial colitis; trophozoites with erythrophagocytosis in amebiasis
• Fecal lactoferrin (marker of mucosal inflammation)
• Multiplex PCR panel (GI pathogen panel) - increasingly used, detects many pathogens simultaneously

Note: Routine ova & parasite testing is low yield for acute bloody diarrhea in high-income countries unless travel history is present. Standard protozoan antigen tests (Giardia, Cryptosporidium) are not appropriate as these do not cause bloody diarrhea.

Blood Tests

• CBC: leukocytosis with bandemia in bacterial colitis; leukemoid reaction with S. dysenteriae type 1
• Metabolic panel: electrolytes, renal function (watch for HUS with EHEC)
• Blood cultures if systemically unwell (positive in <5% of shigellosis)
• LFTs: abnormal if amebic liver involvement

Imaging

• Abdominal X-ray: rule out toxic megacolon (dilated colon), perforation
• CT abdomen/pelvis: if ischemic colitis, perforation, or surgical emergency suspected
• Ultrasound (liver): if amebic liver abscess suspected

Endoscopy

• Colonoscopy/sigmoidoscopy: indicated for chronic/relapsing bloody diarrhea to diagnose IBD, ischemic colitis, or radiation proctitis; not routinely needed for acute infectious colitis

Red Flag Features Requiring Urgent/Inpatient Care

• High fever with systemic toxicity
• Signs of dehydration or hemodynamic instability
• Peritoneal signs (perforation risk)
• Bloody diarrhea in children (HUS risk with EHEC)
• Immunocompromised host
• Elderly with possible ischemic colitis
• Failure to improve after 48 hours of appropriate treatment

IMPORTANT regarding EHEC O157:H7: Do not give antibiotics empirically if EHEC is suspected (absent fever + bloody diarrhea, outbreak setting). Antibiotic use increases the risk of HUS by promoting Shiga toxin release. Wait for culture and toxin results before initiating antibiotics.

Quick Reference: Key Distinguishing Features

Acute + fever + bloody stool + tenesmus → Shigella (most classic)
Acute + NO fever + bloody stool → EHEC O157:H7 (avoid antibiotics!)
Travel + subacute + few PMNs + erythrophagocytosis → E. histolytica
Antibiotic history + bloody/watery stool → C. difficile
Chronic + relapsing + rectal involvement → Ulcerative colitis
Elderly + sudden onset + post-hypotension → Ischemic colitis
Child + colicky pain + "currant jelly" stool → Intussusception

• Symptom to Diagnosis: An Evidence-Based Guide, 4th Ed., pp. 988-1016
• Yamada's Textbook of Gastroenterology, 7th Ed., pp. 3018-3019
• Frameworks for Internal Medicine, pp. 972-1001
• Goldman-Cecil Medicine, International Edition, p. 3228