What is the diagnosis and treatment approach for a patient presenting with symptoms of dysentery, including diarrhea, abdominal pain, and bloody stools?

Dysentery Diagnosis and Treatment

For a patient presenting with dysentery (bloody diarrhea, fever, abdominal pain, tenesmus), obtain stool cultures for Salmonella, Shigella, Campylobacter, Yersinia, and Shiga toxin testing immediately, and initiate empiric antibiotics with azithromycin (or a fluoroquinolone based on local resistance patterns) only if the patient has documented fever in a medical setting with classic bacillary dysentery syndrome, is an infant <3 months old, or has recent international travel with fever ≥38.5°C. 1

Diagnostic Workup

Essential Clinical Features to Assess

• Fever documentation: Temperature ≥38.5°C measured in a medical setting is a key indicator for empiric antibiotic therapy in dysentery 1
• Stool characteristics: Frequent scant bloody stools with mucus, accompanied by tenesmus and abdominal cramps, suggest bacillary dysentery (typically Shigella) 1
• Volume depletion signs: Assess for tachycardia, orthostasis, decreased urination, lethargy, decreased skin turgor, and dry mucous membranes 1
• Travel history: Recent international travel within 3 days prior to symptom onset significantly alters management 1
• Immunocompromised status: HIV/AIDS, immunosuppressive medications, or other immune deficiencies require broader diagnostic evaluation 1

Mandatory Laboratory Testing

• Stool culture: Test for Salmonella, Shigella, Campylobacter, and Yersinia in all patients with fever, bloody stools, severe abdominal cramping, or signs of sepsis 1
• Shiga toxin testing: STEC O157 should be assessed by culture on sorbitol-MacConkey agar, and non-O157 STEC detected by Shiga toxin or genomic assays—this is critical because antibiotics are contraindicated if STEC is identified 1
• Blood cultures: Obtain from infants <3 months, patients with signs of septicemia, suspected enteric fever, or immunocompromised patients 1
• Fecal inflammatory markers: Presence of fecal leukocytes, lactoferrin, or occult blood supports bacterial etiology 1

Special Diagnostic Considerations

• Yersinia testing: Consider in patients with persistent right lower quadrant pain mimicking appendicitis, especially children with exposure to raw/undercooked pork 1
• C. difficile testing: Required if patient received antibiotics within the preceding 8-12 weeks 1
• Parasitic evaluation: Test for Entamoeba histolytica if symptoms persist ≥14 days or if patient is from an endemic region 1

Treatment Algorithm

Immediate Rehydration (All Patients)

• Reduced osmolarity oral rehydration solution (ORS) is the cornerstone of treatment for mild to moderate dehydration, regardless of etiology 1, 2
• Intravenous isotonic fluids (lactated Ringer's) for severe dehydration, shock, altered mental status, or inability to tolerate oral intake 1
• Nasogastric ORS administration may be considered in patients with moderate dehydration who cannot tolerate oral intake 1

Empiric Antibiotic Therapy: When to Treat

Treat empirically in these specific scenarios ONLY:

1. Infants <3 months of age with suspected bacterial etiology: Use third-generation cephalosporin 1, 2

2. Classic bacillary dysentery syndrome: Ill immunocompetent patients with documented fever in a medical setting, abdominal pain, bloody diarrhea, and tenesmus presumptively due to Shigella 1

3. Recent international travelers with temperature ≥38.5°C and/or signs of sepsis 1, 2

4. Immunocompromised patients with severe illness and bloody diarrhea 1

5. Suspected enteric fever with sepsis features: Treat empirically with broad-spectrum antibiotics after obtaining blood, stool, and urine cultures 1

Do NOT treat empirically in immunocompetent adults and children with bloody diarrhea while awaiting diagnostic results, except for the above scenarios 1

Antibiotic Selection

• Adults: Azithromycin (preferred) or fluoroquinolone (ciprofloxacin), depending on local susceptibility patterns and travel history 1, 2

  • Azithromycin is strongly preferred due to high fluoroquinolone resistance in Campylobacter in many regions 2
  • Single-dose azithromycin 1000mg or 500mg daily for 3 days 2, 3

• Children: Azithromycin based on local susceptibility patterns and travel history 1

  • Exception: Third-generation cephalosporin for infants <3 months or those with neurologic involvement 1, 2

• Modify or discontinue antibiotics when a specific pathogen is identified from stool culture 1

Critical Contraindications

NEVER give antibiotics if STEC O157:H7 or other Shiga toxin 2-producing strains are suspected or confirmed—this significantly increases the risk of hemolytic uremic syndrome 1, 2, 3

• Patients with STEC typically present with bloody diarrhea but are NOT febrile at presentation 1
• Wait for Shiga toxin testing results before initiating antibiotics in bloody diarrhea without high fever 2, 3

Adjunctive Therapy

• Antimotility agents (loperamide): May be used in immunocompetent adults with adequate hydration, but NEVER in children <18 years or any patient with fever/bloody diarrhea 2
• Antiemetics (ondansetron): May facilitate oral rehydration in children >4 years 2
• Probiotics: May reduce symptom duration in immunocompetent patients 2

Reassessment and Follow-Up

• Clinical reevaluation is indicated if no improvement within 48-72 hours: Consider antibiotic resistance, inadequate rehydration, or noninfectious causes (inflammatory bowel disease, ischemic colitis) 1
• Persistent symptoms ≥14 days: Reassess for parasitic infections (Giardia, Entamoeba histolytica), inflammatory bowel disease, or postinfectious irritable bowel syndrome 1
• Follow-up stool testing: Generally not recommended after symptom resolution except when required by local health authorities for return to childcare or food-handling employment 1

Common Pitfalls to Avoid

• Empiric antibiotics without fever documentation: Most immunocompetent patients with bloody diarrhea do not require antibiotics while awaiting culture results 1
• Treating STEC with antibiotics: This increases hemolytic uremic syndrome risk—always obtain Shiga toxin testing before treating bloody diarrhea 1, 2, 3
• Neglecting rehydration: ORS is the priority intervention and reduces mortality more effectively than antibiotics alone 1, 2
• Treating asymptomatic contacts: Do not offer empiric antibiotics to contacts; advise infection control measures only 1