Bloody Diarrhea Workup and Management
In immunocompetent adults and children with bloody diarrhea, empiric antibiotics should NOT be started while awaiting diagnostic results, except in specific high-risk scenarios, because antibiotics significantly increase the risk of hemolytic uremic syndrome (HUS) when Shiga toxin-producing E. coli (STEC) is the cause. 1, 2
Initial Clinical Assessment
Critical History Elements
Obtain focused information on:
- Onset and duration: Abrupt vs. gradual, number of days 1
- Stool characteristics: Frequency, volume, presence of mucus or pus 1
- Dysenteric features: Fever documented in medical setting, tenesmus, abdominal cramps, frequent scant bloody stools 1
- Volume depletion signs: Thirst, tachycardia, orthostasis, decreased urination, lethargy, decreased skin turgor 1
- Epidemiological risk factors: Recent international travel, consumption of undercooked ground beef or leafy greens (suggests STEC), raw eggs/shellfish, unpasteurized products, daycare exposure, farm/petting zoo visits, recent antibiotics, immunosuppression (HIV, transplant, chemotherapy) 1, 2
Physical Examination Priorities
- Vital signs: Temperature ≥38.5°C, orthostatic pulse and blood pressure changes 1
- Hydration status: Mucous membrane moisture, skin turgor, jugular venous pulsations 1
- Abdominal examination: Tenderness, peritoneal signs 1, 3
- Mental status: Altered sensorium suggests severe dehydration or sepsis 1, 2
Diagnostic Testing Strategy
When to Test Stool
Obtain stool studies in patients with: 1
- Profuse, bloody, or febrile diarrhea
- Severe dehydration or signs of sepsis
- Immunocompromised state
- Symptoms >7 days
- Suspected outbreak or nosocomial infection
- Infants, elderly, or those with significant comorbidities
Essential Stool Studies
Order the following tests simultaneously: 1, 2
- Stool culture for Salmonella, Shigella, Campylobacter, Yersinia 1
- Shiga toxin testing (EIA or PCR) - critical to detect STEC 2
- Toxin genotyping to differentiate Shiga toxin 1 from toxin 2 (toxin 2 carries higher HUS risk) 1, 2
- C. difficile toxin if recent antibiotic use or healthcare exposure 1
- Fecal leukocytes or lactoferrin to confirm inflammatory process (though may be negative in STEC) 1
Additional Laboratory Testing
For severe cases or specific clinical scenarios: 1
- Complete blood count (assess for anemia, thrombocytopenia suggesting HUS)
- Comprehensive metabolic panel (electrolytes, renal function)
- Blood cultures if fever or sepsis suspected 1
Immediate Management: Rehydration is Paramount
Oral Rehydration Therapy (First-Line)
For mild-moderate dehydration without vomiting or altered mental status: 1, 2
- Use WHO-recommended oral rehydration solution (ORS) containing Na 90 mM, K 20 mM, Cl 80 mM, HCO₃ 30 mM, glucose 111 mM
- Commercial preparations: Pedialyte, Ceralyte, or generic equivalents
- Aggressive hydration during the diarrhea phase reduces risk of oligoanuric renal failure if HUS develops 2
Intravenous Fluids
Indications for IV rehydration: 1, 2
- Severe dehydration
- Hemodynamic instability or shock
- Altered mental status
- Persistent vomiting or ileus
- Inability to tolerate oral fluids
Antibiotic Decision Algorithm
DO NOT Give Empiric Antibiotics If:
Antibiotics are contraindicated when STEC is suspected or confirmed, particularly if Shiga toxin 2 is present or toxin type is unknown, as they significantly increase HUS risk. 1, 2
STEC should be suspected with: 2
- Bloody diarrhea with abdominal tenderness
- Absence of fever at presentation
- Recent consumption of undercooked ground beef or leafy greens
Empiric Antibiotics ARE Indicated For:
Start empiric therapy ONLY in these specific scenarios: 1, 2
Infants <3 months of age with suspected bacterial etiology
- Use third-generation cephalosporin 1
Bacillary dysentery syndrome (presumed Shigella): Ill patients with documented fever in medical setting + abdominal pain + bloody diarrhea + tenesmus + frequent scant bloody stools
Recent international travelers with temperature ≥38.5°C and/or signs of sepsis
- Fluoroquinolone OR azithromycin depending on travel destination and local resistance 1
Immunocompromised patients with severe illness and bloody diarrhea
- Consider empiric broad-spectrum therapy 1
Suspected enteric fever with sepsis features
- Obtain blood, stool, and urine cultures first, then start broad-spectrum antibiotics 1
Antibiotic Selection
- Fluoroquinolone resistance is increasing, particularly in South/Southeast Asia - use azithromycin for travelers from these regions 1
- Avoid antibiotics entirely if STEC producing Shiga toxin 2 is identified or if toxin genotype is unknown 1, 2
Critical Pitfalls to Avoid
Never Do These:
- Do not give antibiotics empirically for bloody diarrhea without first excluding STEC - this increases HUS risk 2
- Do not use antimotility agents (loperamide) in children <18 years or any patient with bloody diarrhea until STEC is excluded 2
- Do not neglect aggressive rehydration while focusing on antimicrobial decisions - dehydration is a major risk factor for HUS complications and mortality 2
- Do not delay stool testing in patients meeting criteria - rapid microbiologic diagnosis is essential 3
Monitoring and Follow-Up
All Patients with Bloody Diarrhea Require:
- Serial monitoring for HUS development: Watch for hemolytic anemia, thrombocytopenia, acute renal failure 2
- Reassessment if no improvement: Consider fluid/electrolyte balance, nutritional status, and non-infectious causes (inflammatory bowel disease, ischemic colitis) if symptoms persist ≥14 days 1
- Serial abdominal examinations in severe cases 1, 2
Special Considerations for Immunocompromised Patients
Hospitalize and evaluate aggressively with: 1
- Complete blood count, electrolytes
- Stool work-up including C. difficile, Salmonella, E. coli, Campylobacter
- Consider neutropenic enterocolitis if neutropenic - requires broad-spectrum antibiotics covering gram-negatives, gram-positives, and anaerobes (piperacillin-tazobactam OR imipenem-cilastatin OR cefepime/ceftazidime + metronidazole) 1