CLINICAL PRINTABLE
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A one-page Diarrhea clinical reference is on the way.
1 · Recognition / Alarm Features
- Acute diarrhea: ≥3 loose or watery stools per day for <14 days. Persistent diarrhea: 14–29 days. Chronic diarrhea: ≥30 days. Duration guides the differential and workup.
- Alarm features requiring urgent evaluation: bloody or mucoid stool, fever >38.5°C, severe abdominal pain, signs of dehydration, immunocompromised state, age >70, recent hospitalization or antibiotic use, or symptoms lasting >7 days without improvement.
- Inflammatory diarrhea (dysentery): bloody stool, fever, tenesmus, fecal leukocytes. Suggests invasive pathogens (Salmonella, Shigella, Campylobacter, E. coli O157:H7, C. diff) or IBD. Requires stool culture and targeted treatment.
- Noninflammatory diarrhea: watery, no blood, no fever, no fecal leukocytes. Suggests viral gastroenteritis, toxin-mediated illness, or osmotic causes. Usually self-limited. Supportive care is appropriate.
- Traveler's diarrhea: onset within 2 weeks of international travel, typically watery. Most commonly ETEC. Azithromycin is first-line (especially in South/Southeast Asia due to fluoroquinolone resistance). Rifaximin for non-invasive traveler's diarrhea.
2 · Differential / Secondary Causes
Viral gastroenteritis
Most common cause of acute diarrhea. Norovirus, rotavirus, adenovirus. Watery diarrhea, nausea, vomiting, low-grade fever. Self-limited 1–3 days. No antibiotics. Oral rehydration.
C. difficile colitis
Watery diarrhea (≥3 unformed stools/24 hours) after antibiotics or healthcare exposure. Test with NAAT or GDH/toxin EIA. Do not test formed stool. Treat with oral vancomycin or fidaxomicin. See C. diff Deep Dive.
Inflammatory bowel disease (IBD)
Crohn's disease or ulcerative colitis. Bloody diarrhea, abdominal pain, weight loss, extraintestinal manifestations. Persistent or recurrent course. Colonoscopy with biopsy for diagnosis. Gastroenterology referral.
Microscopic colitis
Chronic watery diarrhea in older adults (especially women). Normal colonoscopy appearance — diagnosis requires biopsy. Associated with NSAIDs, PPIs, SSRIs. Treat by stopping offending agent; budesonide for refractory cases.
Medication-induced diarrhea
Antibiotics (most common), metformin, laxatives, magnesium-containing antacids, colchicine, SSRIs, chemotherapy. Review the medication list at every diarrhea visit. Stopping the offending agent is the most effective treatment.
Malabsorption
Celiac disease, lactose intolerance, pancreatic exocrine insufficiency, small intestinal bacterial overgrowth (SIBO). Fatty, bulky, foul-smelling stools (steatorrhea). Weight loss. Celiac serology (tTG-IgA), lactose breath test, fecal elastase.
3 · Treatment Pathway
Oral rehydration — cornerstone of management
Oral rehydration solution (ORS) for mild-to-moderate dehydration. WHO ORS or commercial preparations. Sports drinks are not ideal (too high in sugar, too low in sodium). IV fluids for severe dehydration, inability to tolerate oral intake, or hemodynamic compromise.
Diet
Early refeeding is recommended — the BRAT diet is no longer endorsed. Resume regular diet as tolerated. Avoid dairy temporarily if lactose intolerance is suspected. Avoid high-fat, high-fiber foods acutely.
Antimotility agents
Loperamide for watery, noninflammatory diarrhea without fever or bloody stool. Reduces stool frequency and duration. Avoid in bloody diarrhea, suspected C. diff, or invasive bacterial infection — may worsen disease or precipitate toxic megacolon.
Antibiotics — targeted, not empiric
Most acute diarrhea does not require antibiotics. Indications: severe illness, immunocompromised host, traveler's diarrhea, confirmed bacterial pathogen requiring treatment (Shigella, Campylobacter in severe cases). Azithromycin is preferred for most bacterial causes. Avoid fluoroquinolones for Campylobacter (high resistance).
Persistent diarrhea workup
Stool studies: culture, ova and parasites (Giardia, Cryptosporidium), C. diff NAAT, fecal calprotectin (elevated in IBD, low in IBS). CBC, CMP, TSH, celiac serology. Colonoscopy with biopsy if no diagnosis after initial workup.
4 · Expected Response
- Viral gastroenteritis: self-limited, resolves in 1–3 days. Reassure and hydrate.
- Traveler's diarrhea treated with azithromycin: symptom improvement within 24–48 hours.
- C. diff treated with oral vancomycin: improvement within 2–4 days. Recurrence rate 15–25% after first episode — higher with each subsequent episode.
- Persistent diarrhea not improving after 14 days: expand workup. Do not continue empiric management without a diagnosis.
5 · Escalation
- Severe dehydration, hemodynamic instability, or inability to maintain oral intake: IV fluids and hospital admission.
- Bloody diarrhea with fever and systemic toxicity: evaluate for hemolytic uremic syndrome (HUS) — especially with E. coli O157:H7. Avoid antibiotics and antimotility agents in suspected STEC infection.
- Toxic megacolon (severe C. diff or IBD): abdominal distension, fever, leukocytosis, tachycardia. Urgent surgical evaluation.
- Persistent diarrhea >30 days without diagnosis: gastroenterology referral for colonoscopy, small bowel evaluation, and specialized testing.
Apply It · Change One Detail
APPLY IT
A 34-year-old returns from Mexico with 3 days of watery diarrhea, cramping, and low-grade fever. No blood in stool. No systemic toxicity. This is traveler's diarrhea — most likely ETEC. Azithromycin 1 g single dose or 500 mg daily for 3 days. Oral rehydration. Loperamide can be added for symptom relief. No stool cultures needed for uncomplicated traveler's diarrhea.
CHANGE ONE DETAIL
Change one detail — the same patient returns from Southeast Asia with bloody diarrhea, high fever, and severe cramping. Now the picture changes: invasive bacterial diarrhea (Shigella, Campylobacter) is more likely. Stool culture is indicated. Azithromycin remains first-line. Do NOT use loperamide with bloody diarrhea — it can worsen invasive infection and increase the risk of HUS with STEC.
Bottom Line
Most acute diarrhea is self-limited and does not need antibiotics. The key decision point is inflammatory vs noninflammatory: bloody stool, fever, and fecal leukocytes point toward invasive pathogens that may need treatment.
EVIDENCE & REFERENCES
- Riddle MS, et al. ACG Clinical Guideline: Diagnosis, Treatment, and Prevention of Acute Diarrheal Infections in Adults. Am J Gastroenterol. 2016;111(5):602-622. doi:10.1038/ajg.2016.126
- Shane AL, et al. 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea. Clin Infect Dis. 2017;65(12):e45-e80. doi:10.1093/cid/cix669
- DuPont HL. Acute infectious diarrhea in immunocompetent adults. N Engl J Med. 2014;370(16):1532-1540. doi:10.1056/NEJMra1301069