Enteritis is inflammation of the small-bowel mucosa, most often triggered by infection, drugs, or autoimmune disease. It may occur alone or together with gastritis (gastroenteritis) or colitis (enterocolitis). Because the jejunum and ileum handle digestion, fluid balance, and nutrient absorption, their inflammation produces a characteristic cluster of abdominal and systemic signs that differ from pure colonic disorders.

1. Core intestinal symptoms
   • Diarrhea: typically watery or loose, occasionally fatty and foul-smelling when bile-acid absorption is impaired; volume ranges from a few episodes daily to profuse stool every hour.
   • Cramping periumbilical pain: colicky waves that build and recede, often relieved transiently by passage of stool or flatus.
   • Hyperactive bowel sounds: audible gurgling or splashing without a stethoscope during active phases.
   • Bloating and distension: gas trapped in dilated loops plus mild ileus.
   • Nausea and early satiety: more common when the stomach is also involved.
2. Systemic and volume clues
   • Low-grade fever 37.5–38.5 °C in viral or mild bacterial cases; >39 °C suggests invasive organisms.
   • Fatigue, myalgia, and headache: cytokine-mediated response.
   • Thirst, decreased urine output, postural dizziness: early dehydration.
   • Sunken eyes, delayed skin turgor, hypotension: moderate to severe fluid loss, especially when diarrhea exceeds eight stools per day.
3. Variant patterns by cause
   • Viral enteritis (rotavirus, norovirus): vomiting often precedes diarrhea, fever mild, resolution within 3–5 days.
   • Bacterial toxins (Bacillus cereus, Staph aureus): sudden cramps and watery stools 1–6 h after contaminated food, short duration.
   • Invasive bacteria (Campylobacter, Salmonella): fever >38.5 °C, loose stools may become bloody, white blood cells visible on stool smear.
   • Drug-induced (NSAIDs, chemotherapy, metformin): diffuse mild cramps, watery diarrhea, often no fever; symptoms abate when medication is paused.
   • Autoimmune (celiac, Crohn enteritis): chronic or relapsing cramps, steatorrhea, weight loss, associated skin or joint manifestations.
4. Associated features suggesting complications
   • Blood mixed with stool: implies mucosal ulceration or severe inflammation extending into the colon.
   • Nocturnal diarrhea: raises possibility of proximal extension or inflammatory bowel disease.
   • Marked distension and obstipation: consider toxic megacolon or severe ileus.
   • Oral aphthae, rash, or joint pain: systemic autoimmune process.
5. Red-flag combinations demanding urgent evaluation
   Continuous diarrhea >10 stools per day with orthostatic hypotension, bloody stool plus fever >39 °C, severe abdominal distension or localized rebound tenderness, and weight loss >5 % within two weeks.

Summary table