Definition and epidemiology
Enteritis refers to inflammation of the small intestine (duodenum, jejunum, ileum). It is frequently grouped with colitis as "gastroenteritis" when the stomach and colon are also involved, but strictly refers to small bowel pathology.
Enteritis is categorized by etiology:
- Infectious enteritis (A02, A09): viral, bacterial, or parasitic. Viral causes (rotavirus, norovirus) are the leading cause of acute diarrhea in children worldwide and a major cause of pediatric mortality in low-resource settings.
- Non-infectious enteritis: ischemic enteritis (K55), radiation enteritis (post-pelvic/abdominal radiotherapy), and regional enteritis (Crohn disease, K50), which is a chronic granulomatous inflammatory process rather than an infection.
Infectious enteritis is extremely common globally; diarrheal disease remains among the top causes of death in children under 5 in developing regions, though mortality has fallen substantially with oral rehydration therapy and vaccination programs.
- Rotavirus and norovirus are the leading causes of acute viral enteritis worldwide
- Oral rehydration therapy is the single most important intervention in acute infectious enteritis
- Avoid antimotility agents and antibiotics in suspected EHEC due to hemolytic uremic syndrome risk
- Campylobacter jejuni is linked to Guillain-Barre syndrome; Shigella/Salmonella/Yersinia to reactive arthritis
- Giardia causes malabsorptive diarrhea without mucosal invasion; diagnosed via stool antigen testing
- Crohn disease causes transmural, skip-lesion inflammation anywhere from mouth to anus, most often terminal ileum
- Ischemic enteritis presents with pain out of proportion to physical exam findings
- Radiation enteritis occurs after pelvic/abdominal radiotherapy and can be acute or chronic
Etiology and risk factors
Infectious causes
| Category | Examples |
|---|---|
| Viral | Rotavirus, norovirus, adenovirus, astrovirus |
| Bacterial | Salmonella, Campylobacter, Shigella, E. coli (including enterotoxigenic/EHEC), Yersinia, Vibrio cholerae |
| Parasitic | Giardia lamblia, Cryptosporidium, Entamoeba histolytica |
Non-infectious causes
- Ischemic enteritis: mesenteric atherosclerosis, embolism, or low-flow states in critically ill patients.
- Radiation enteritis: following pelvic or abdominal radiotherapy, acute (during treatment) or chronic (months to years later).
- Crohn disease: autoimmune/dysregulated immune response, genetic predisposition (NOD2 variants), smoking as a major risk factor.
- Drug-induced: NSAIDs, chemotherapy agents.
Risk factors
- Contaminated food or water, poor sanitation
- International travel
- Immunosuppression (HIV, transplant, chemotherapy)
- Daycare or institutional settings (fecal-oral spread)
- Recent antibiotic use (predisposes to C. difficile, though this primarily causes colitis)
- Vascular disease and atrial fibrillation (ischemic enteritis)
- Prior pelvic radiotherapy
Pathophysiology
Mechanisms vary by cause:
- Viral: Rotavirus and norovirus infect and destroy mature enterocytes at the tips of small intestinal villi, impairing absorption and causing secretory diarrhea via enterotoxin-like effects (e.g., rotavirus NSP4 protein).
- Bacterial - enterotoxigenic: Toxins (e.g., cholera toxin, ETEC heat-labile/heat-stable toxins) activate adenylate/guanylate cyclase, increasing cAMP/cGMP and driving chloride and water secretion into the lumen (secretory diarrhea), typically without mucosal invasion.
- Bacterial - invasive: Salmonella, Shigella, Campylobacter, and EHEC invade or damage the mucosa, triggering inflammatory diarrhea with possible blood and leukocytes in stool.
- Giardia: Trophozoites attach to the duodenal/jejunal brush border, causing malabsorption without invasion.
- Ischemic enteritis: Reduced mesenteric blood flow causes mucosal hypoxia, progressing to transmural necrosis if prolonged.
- Radiation enteritis: Direct DNA damage to rapidly dividing crypt epithelial cells; chronic phase involves vascular sclerosis and fibrosis.
- Crohn disease: Dysregulated Th1/Th17 immune response to luminal antigens in a genetically susceptible host, producing transmural granulomatous inflammation with skip lesions.
Clinical features
- Diarrhea (watery in secretory/viral causes; may be bloody in invasive bacterial causes)
- Abdominal cramping and pain
- Nausea and vomiting
- Low-grade fever (higher fevers suggest invasive bacterial infection)
- Signs of dehydration: dry mucous membranes, decreased urine output, tachycardia, hypotension in severe cases
- Weight loss and malabsorption (chronic causes: Giardia, Crohn, radiation enteritis)
- Ischemic enteritis: severe pain out of proportion to exam, possible bloody stool, systemic toxicity if advanced
- Crohn disease: additional extraintestinal features (arthritis, uveitis, erythema nodosum, aphthous ulcers) and perianal disease
Diagnosis
Diagnosis is largely clinical for self-limited acute infectious enteritis; further workup is reserved for severe, persistent, or atypical presentations.
Initial evaluation
- History: duration, travel, food exposure, sick contacts, antibiotic use, immunosuppression
- Assessment of hydration status and vital signs
Laboratory and stool studies (when indicated)
- Stool culture, fecal leukocytes, stool ova and parasites (if prolonged, bloody, or travel-associated)
- Stool antigen/PCR panels for viral and bacterial pathogens
- Giardia antigen testing or microscopy if suspected
- Basic metabolic panel to assess electrolyte derangement and renal function in dehydrated patients
Imaging and endoscopy
- CT angiography for suspected ischemic enteritis
- CT or MR enterography and endoscopy with biopsy for suspected Crohn disease (shows transmural inflammation, skip lesions, granulomas)
- Endoscopy generally not needed for typical acute infectious enteritis
Differential diagnosis
- Gastroenteritis/colitis: overlapping symptoms; colitis favors bloody diarrhea with tenesmus and lower abdominal/rectal involvement
- Irritable bowel syndrome: chronic, no systemic signs, normal labs
- Celiac disease: chronic malabsorption, villous atrophy, serology (anti-tTG)
- Ulcerative colitis: continuous colonic involvement, bloody diarrhea, no skip lesions (vs Crohn)
- Appendicitis: localized right lower quadrant pain, may mimic terminal ileitis
- Mesenteric ischemia (acute): severe pain out of proportion to exam, vascular risk factors
- Medication-induced diarrhea: NSAIDs, chemotherapy, laxative overuse
Management
Acute infectious enteritis
- Oral rehydration therapy (ORT) is first-line and most important intervention; IV fluids for severe dehydration or inability to tolerate oral intake
- Antiemetics may be used for vomiting
- Antimotility agents (e.g., loperamide) are generally avoided in suspected invasive bacterial infection or bloody diarrhea due to risk of prolonging illness or precipitating toxic megacolon
- Antibiotics are not routinely indicated for most bacterial enteritis (self-limited) but are used for specific situations: severe Shigella, Campylobacter in immunocompromised patients, cholera, or parasitic infections (metronidazole or tinidazole for Giardia)
- Antibiotics are specifically avoided in suspected EHEC (Shiga toxin-producing E. coli) due to increased risk of hemolytic uremic syndrome
Ischemic enteritis
- Bowel rest, IV fluids, correction of underlying cause (e.g., anticoagulation or revascularization for embolic disease)
- Surgical resection if transmural infarction or perforation
Radiation enteritis
- Supportive care, dietary modification (low-fiber, low-fat); chronic strictures may require surgery
Crohn disease (regional enteritis)
- Induction and maintenance with corticosteroids (induction only), aminosalicylates (limited efficacy in Crohn), immunomodulators (azathioprine, methotrexate), and biologics (anti-TNF agents, anti-integrin, anti-IL-12/23 agents) per American College of Gastroenterology and European Crohn's and Colitis Organisation guidance
- Smoking cessation is strongly recommended
- Surgery for strictures, fistulas, or medically refractory disease (not curative in Crohn, unlike ulcerative colitis)
Complications and prognosis
- Dehydration and electrolyte imbalance: most common complication of acute infectious enteritis, can be life-threatening in young children and the elderly
- Hemolytic uremic syndrome: associated with Shiga toxin-producing E. coli (EHEC O157:H7)
- Reactive arthritis: following Salmonella, Shigella, Campylobacter, or Yersinia infection
- Guillain-Barre syndrome: associated with Campylobacter jejuni
- Bowel infarction and perforation: in untreated ischemic enteritis
- Strictures and fistulas: chronic radiation enteritis or Crohn disease
- Malnutrition and malabsorption: chronic parasitic or Crohn-related enteritis
Most acute infectious enteritis is self-limited and resolves within days with supportive care. Prognosis is excellent with adequate rehydration; mortality is largely preventable but remains significant in resource-limited settings, especially among infants. Crohn disease and radiation enteritis follow a chronic, relapsing course requiring long-term management.
"SCRAM" for invasive, bloody-diarrhea bacterial/parasitic causes: Salmonella, Campylobacter, (R)entamoeba histolytica (amoeba), Shigella, EHEC (enterohemorrhagic E. coli) — remember these invade or produce cytotoxins that damage the mucosa, causing inflammatory, often bloody diarrhea. By contrast, watery/non-bloody secretory diarrhea comes from toxin-mediated or viral causes that spare the mucosa: Vibrio cholerae, ETEC, rotavirus, and norovirus.
Practice questions
1. A 6-year-old boy develops profuse watery diarrhea and vomiting two days after starting daycare. He has no fever and no blood in stool. Stool studies reveal a non-enveloped double-stranded RNA virus. Which of the following best describes the mechanism of diarrhea in this condition?
2. A 68-year-old woman with atrial fibrillation not on anticoagulation presents with sudden severe abdominal pain that is disproportionate to a relatively benign abdominal exam. She has nausea and one episode of bloody stool. Lactate is elevated. Which diagnosis is most likely?
3. A 24-year-old man with a 3-month history of intermittent right lower quadrant pain, non-bloody diarrhea, and a 10-lb weight loss is found on colonoscopy and biopsy to have transmural inflammation with granulomas and skip lesions involving the terminal ileum, with sparing of the rectum. He is a current smoker. Which of the following is most appropriate as part of long-term management?
Frequently asked questions
What causes enteritis?
Enteritis is most often caused by viral infections (rotavirus, norovirus), bacterial pathogens (Salmonella, Campylobacter, E. coli, Shigella), or parasites (Giardia). Non-infectious causes include ischemia, radiation therapy, and Crohn disease. The cause determines whether diarrhea is watery (secretory, toxin-mediated) or bloody (invasive mucosal damage).
What are the first symptoms of enteritis?
The earliest symptoms are usually watery diarrhea, abdominal cramping, nausea, and low-grade fever, sometimes preceded by vomiting. Symptoms typically begin within hours to a few days of exposure to a pathogen. Bloody stool or high fever suggests a more invasive bacterial cause rather than typical viral enteritis.
How is enteritis diagnosed?
Most acute infectious enteritis is diagnosed clinically based on history and exam without extensive testing. Stool studies, including culture, PCR panels, or antigen testing, are reserved for severe, bloody, persistent, or travel-related cases. Imaging or endoscopy is used only when ischemia or Crohn disease is suspected.
Is enteritis curable?
Acute infectious enteritis is almost always self-limited and resolves completely within days with supportive care such as oral rehydration. Parasitic causes like Giardia are curable with appropriate antiparasitic therapy. Chronic causes such as Crohn disease are not curable but can be effectively controlled with long-term medical management.
Enteritis vs colitis — what is the difference?
Enteritis refers to inflammation of the small intestine, while colitis refers to inflammation of the colon (large intestine). Enteritis more often causes watery, non-bloody diarrhea and malabsorption, whereas colitis more often causes bloody diarrhea, tenesmus, and lower abdominal cramping. Many infections and inflammatory bowel diseases can affect both regions simultaneously.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: K55
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.