Bloody Diarrhea, Vomiting, Fever, and Stomach Cramps: Infectious and Non-Infectious Causes

This symptom cluster suggests invasive enteric infection or inflammatory bowel disease. Prompt evaluation is needed to guide therapy and public health reporting.

Infectious Causes

Category	Key Pathogens	Typical Features
Bacterial	Salmonella (non-typhoidal), Shigella, Campylobacter, E. coli O157:H7 (STEC), Yersinia, C. difficile	Fever, blood/mucus, tenesmus; STEC → HUS risk
Viral	Norovirus, Rotavirus, Adenovirus 40/41, Astrovirus	Vomiting prominent; bloody diarrhea less common (except severe)
Parasitic	Entamoeba histolytica, Giardia (rarely bloody), Cryptosporidium, Cyclospora	Subacute/chronic; travel/exposure history

Non-Infectious Causes

• Inflammatory Bowel Disease (IBD): Ulcerative colitis (bloody diarrhea, urgency), Crohn's (pain, weight loss, perianal disease).
• Ischemic Colitis: Sudden pain, bleeding in >60yo with vascular disease.
• Diverticular Bleeding: Painless hematochezia; but diverticulitis = pain + fever.
• Drug-Induced: NSAIDs, antibiotics (C. diff), anticoagulants, checkpoint inhibitors.
• Food Allergy/Intolerance: Cow's milk protein (infants), FPIES.
• Acute Abdomen: Appendicitis (rarely bloody), intussusception (currant jelly stool), toxic megacolon (IBD/C. diff complication).

When to Seek Urgent Care

• Signs of dehydration (dry mouth, ↓urine, dizziness).
• High fever (>38.5°C / 101.3°F).
• Severe abdominal pain or distension.
• Large volume blood or black tarry stool.
• Immunocompromised, elderly, pregnant.
• Symptoms >3 days (adults) or >24h (children).

Initial Workup

• Stool: culture, multiplex PCR panel, C. diff toxin, ova/parasites.
• CBC, electrolytes, renal function, CRP.
• Blood cultures if febrile/septic.
• Imaging (CT abdomen/pelvis) if surgical abdomen suspected.

Empiric antibiotics not recommended for most acute diarrhea (prolongs carriage, HUS risk with STEC). Targeted therapy after pathogen ID.