Diagnosis: Acute Infectious Colitis (Bacillary Dysentery / Invasive Bacterial Gastroenteritis)

Clinical Picture

Most Likely Organisms (in order of probability)

1. Shigella species (Bacillary Dysentery) - most classic cause of bloody diarrhea with colicky abdominal pain and tenesmus. Fever develops 1-3 days post-infection, followed by abdominal cramps and bloody diarrhea. About 50% have grossly bloody stools. - Yamada's Textbook of Gastroenterology
2. Campylobacter jejuni - prominent abdominal pain (sometimes before diarrhea), bloody stools, linked to undercooked food from outside.
3. Salmonella species - associated with eggs, poultry, meat; bloody diarrhea with abdominal pain.
4. Enteroinvasive / Shiga toxin-producing E. coli (STEC/EIEC) - initial watery diarrhea progressing to bloody hemorrhagic colitis with abdominal cramps, little or no fever. Linked to contaminated food eaten outside. - Medical Microbiology, 9e
5. Entamoeba histolytica (Amoebic Dysentery) - should be considered especially if the history involves eating in unhygienic conditions; causes flask-shaped ulcers and bloody dysentery.

Why NOT Other Diagnoses

• Hemorrhoids / fissure / rectal pathology - explicitly ruled out by history (no anal or rectal pathology found)
• IBD (Ulcerative colitis / Crohn's) - possible but less acute onset, no prior history mentioned; infectious etiology more consistent with the food exposure trigger
• Ischemic colitis - typically in older patients with vascular risk factors
• Upper GI bleed - drops of bright red blood with stool suggests lower GI source, not melena

Pathophysiology

• Mucosal inflammation and ulceration
• Submucosal hemorrhage - visible red blood per rectum
• Colonic spasm and cramps - abdominal pain
• Tenesmus (may be present)

Workup to Confirm

1. Stool culture and microscopy - for Shigella, Salmonella, Campylobacter, E. coli, ova & cysts (amoeba)
2. Stool for occult blood (already clinically apparent)
3. CBC - leukocytosis suggests bacterial/invasive etiology
4. CRP / ESR
5. Sigmoidoscopy/colonoscopy if not resolving - to rule out IBD

Management Outline

• Rehydration - oral/IV depending on severity
• Antibiotics - for confirmed/suspected Shigella or Campylobacter (azithromycin, ciprofloxacin based on local resistance patterns)
• Avoid antidiarrheals (e.g., loperamide) in invasive colitis - can worsen the course
• Rest and dietary modification

Rosen's Emergency Medicine, Schwartz's Principles of Surgery, and Yamada's Textbook of Gastroenterology all confirm that bloody diarrhea with abdominal pain following food exposure is characteristic of invasive bacterial colitis, with Shigella, Campylobacter, and Salmonella as the leading culprits.

First-Line Management Plan

Step 1 - Assess Severity First

A. Rehydration (Most Important Step)

• WHO Oral Rehydration Solution (ORS) - reduced osmolarity formula
  • 75 mmol/L Na+, 20 mmol/L K+, 65 mmol/L Cl-, 75 mmol/L glucose
  • Give 200-400 mL after each loose stool
  • Target: 1 litre ORS per hour for first 4 hours (rehydration phase), then maintenance 200 mL/hr
  • For 65 kg adult with moderate dehydration: approximately 2-3 litres in first 4 hours

• IV Lactated Ringer's Solution (preferred over normal saline) OR Normal Saline
  • 100 mL/kg over 3-4 hours = 6,500 mL total for 65 kg patient (divide: rapid infusion 30 mL/kg in first 30 min for shock, then remainder over remaining time)
  • Practical: 1 litre NS/RL over 30 min bolus if hypotensive, then reassess
  • Maintenance: 30-40 mL/kg/day = ~2-2.5 litres/day

B. Antibiotics

Indication: Patient has bloody stool + abdominal pain with moderate-severe presentation - empiric antibiotic therapy is warranted.

• Goldman-Cecil Medicine: "For adults, empirical oral ciprofloxacin (500 mg orally once daily for 3 days) is recommended"

C. Symptomatic Relief

AVOID antidiarrheal agents (loperamide, diphenoxylate) - these are contraindicated in invasive/bloody diarrhea. They can prolong symptoms and delay bacterial clearance. - Robbins Pathologic Basis of Disease and Sleisenger & Fordtran's GI

D. Diet

• NPO is NOT required - early oral feeding is encouraged
• Start with BRAT diet (Banana, Rice, Applesauce, Toast) or soft low-fibre foods
• Avoid dairy, spicy food, raw vegetables until recovery
• Avoid caffeine and alcohol (worsen motility)
• Bananas specifically - promote short-chain fatty acid production, help colonocyte repair

E. Investigations to Order Simultaneously

1. Stool routine microscopy + culture - to identify organism and sensitivity (guides antibiotic switch if needed)
2. Stool for ova & cysts - to rule out amoebic dysentery
3. CBC - WBC count, haemoglobin (assess blood loss)
4. CRP / ESR
5. Serum electrolytes + creatinine - assess hydration and renal function
6. LFT if prolonged course

F. Red Flags - When to Hospitalize

• Profuse PR bleeding / haemodynamic instability
• Inability to maintain oral hydration
• High fever > 39°C not responding to antipyretics
• Signs of peritonism (toxic megacolon, perforation)
• No improvement after 48 hours of outpatient antibiotics

Summary Drug Card for This Patient (65 kg, 24 yr)

Sources: Goldman-Cecil Medicine, 2 Volume Set; Sleisenger & Fordtran's GI and Liver Disease; Rosen's Emergency Medicine