One-liner#

Evaluate acute diarrhea (<2 weeks) to identify patients needing testing or antibiotics while managing the majority with supportive care alone, avoiding unnecessary stool studies and antibiotics in self-limited viral gastroenteritis.

Quick nav#

• Red flags / send to ED
• Key history
• Focused exam
• Differential (quick pattern recognition)
• Workup
• Initial management
• Management by diagnosis
• Follow-up
• Patient instructions
• Smartphrase snippets

Red flags / send to ED#

• Severe dehydration: hypotension, tachycardia, altered mental status, oliguria
• Bloody diarrhea with fever and hemodynamic instability
• Severe abdominal pain with peritoneal signs
• Toxic appearance (high fever, rigors, severe illness)
• Immunocompromised with severe symptoms
• Elderly with significant volume depletion
• Suspected hemolytic uremic syndrome (HUS): bloody diarrhea + AKI + thrombocytopenia

Key history#

Stool characteristics:

• Frequency: number of stools per day (>3 loose stools = diarrhea)
• Consistency: watery (secretory/osmotic), bloody (inflammatory/invasive), fatty/greasy (malabsorption)
• Volume: large volume (small bowel) vs small frequent (colonic)
• Blood/mucus: suggests inflammatory or invasive process
• Nocturnal diarrhea: suggests organic cause (not functional)

Timeline:

• Onset: sudden (infectious, toxin) vs gradual
• Duration: <14 days = acute; 14–30 days = persistent; >30 days = chronic
• Incubation period helps identify pathogen (see table below)

Exposure history (critical):

• Food: undercooked meat/poultry (Salmonella, Campylobacter), raw seafood (Vibrio), eggs (Salmonella), unpasteurized dairy (Listeria, Campylobacter), rice (B. cereus)
• Water: untreated water, travel (Giardia, Cryptosporidium)
• Travel: developing countries (ETEC most common), camping/hiking
• Sick contacts: household members, daycare, nursing home
• Recent antibiotics: C. difficile (can occur up to 3 months after antibiotics)
• Hospitalization: C. difficile, resistant organisms
• Sexual history: MSM (Shigella, Giardia, amebiasis, LGV proctitis)
• Immunocompromised: broader differential including opportunistic infections

Incubation periods:

Associated symptoms:

• Fever: suggests invasive/inflammatory process
• Vomiting: prominent in viral gastroenteritis, S. aureus toxin
• Abdominal pain: crampy (infectious), severe (C. diff, ischemia)
• Tenesmus: rectal urgency, suggests colitis
• Myalgias, headache: viral prodrome

Focused exam#

• Vitals: fever, orthostatic hypotension, tachycardia
• General: hydration status (mucous membranes, skin turgor, capillary refill)
• Abdominal: tenderness (diffuse vs localized), distension, bowel sounds, peritoneal signs
• Rectal: if bloody diarrhea—assess for gross blood, masses, fissures
• Skin: rash (viral exanthem, reactive arthritis)

Differential (quick pattern recognition)#

Common/likely (outpatient)#

Can’t-miss / urgent#

Workup#

Most patients with acute diarrhea need NO testing—viral gastroenteritis is self-limited.

When to test:

• Bloody diarrhea
• Fever >101.3°F (38.5°C)
• Severe or prolonged symptoms (>7 days)
• Recent antibiotic use (C. diff)
• Immunocompromised
• Hospitalized patients
• Outbreak investigation
• High-risk food handlers, healthcare workers, daycare

Stool studies:

Labs:

• BMP: if moderate-severe dehydration (assess electrolytes, renal function)
• CBC: if bloody diarrhea or severe illness (WBC, platelets for HUS)

When NOT to test:

• Mild, self-limited diarrhea <3 days without fever or blood
• Clear viral gastroenteritis with sick contacts
• Obvious dietary indiscretion

Initial management#

• Assess hydration: Most can be managed with oral rehydration
• Oral rehydration: WHO-ORS, Pedialyte, or homemade (1L water + 6 tsp sugar + ½ tsp salt)
• Diet: Clear liquids initially; advance to bland diet as tolerated; avoid dairy, caffeine, alcohol
• Antidiarrheals: Use with caution (see below)
• Antibiotics: NOT routine—most acute diarrhea is viral and self-limited

Antidiarrheal use:

Management by diagnosis#

Viral gastroenteritis#

Education:

• Most common cause of acute diarrhea; usually norovirus in adults
• Self-limited; resolves in 1–3 days
• Highly contagious; hand hygiene critical

Treatment:

• Oral rehydration
• Antiemetics if needed (ondansetron)
• Loperamide if no fever or blood
• NO antibiotics

Follow-up: Return if not improving in 3 days, bloody stool, high fever, or signs of dehydration.

Traveler’s diarrhea#

Education:

• Usually bacterial (ETEC most common); acquired from contaminated food/water
• Most cases self-limited in 3–5 days
• Prevention: “Boil it, cook it, peel it, or forget it”

Treatment:

Mild (tolerable, not interfering with activities):

• Oral rehydration
• Loperamide PRN
• Antibiotics optional

Moderate-severe (interfering with activities) or dysentery:

• Antibiotics shorten duration by 1–2 days

Follow-up: Should improve within 24–48 hours of antibiotics; if not, consider resistant organism or alternative diagnosis.

C. difficile infection#

Education:

• Caused by antibiotic disruption of normal gut flora
• Highly contagious; spread by spores
• Recurrence common (20–30%); probiotics may help prevent

Treatment:

First episode, non-severe (WBC <15K, Cr <1.5):

First episode, severe (WBC ≥15K or Cr ≥1.5):

• Vancomycin 125 mg QID x 10 days (oral)
• If fulminant (hypotension, ileus, megacolon): ED/hospital for IV metronidazole + high-dose oral/rectal vancomycin + surgical consult

Recurrent C. diff:

• First recurrence: Vancomycin taper/pulse OR fidaxomicin
• Multiple recurrences: GI referral for fecal microbiota transplant (FMT)

Adjunctive measures:

• Stop inciting antibiotic if possible
• Avoid loperamide
• Contact precautions
• Consider probiotics (S. boulardii) for prevention of recurrence

Follow-up: Clinical improvement expected in 3–5 days. Do NOT retest for cure—PCR remains positive for weeks. Retest only if symptoms recur after initial improvement.

Invasive bacterial diarrhea (Shigella, Salmonella, Campylobacter)#

Education:

• Bacterial infection of the intestine; usually from contaminated food
• Most cases self-limited but antibiotics may shorten duration
• Salmonella: antibiotics may prolong carriage; reserve for severe cases

Treatment:

When to treat:

• Shigella: always treat (highly contagious, prevents complications)
• Campylobacter: treat if severe or early in course (<3 days)
• Salmonella (non-typhoidal): treat only if severe, immunocompromised, age >50 with atherosclerosis, or prosthetic hardware

Follow-up: Improvement expected in 2–3 days. If not improving, reassess diagnosis and consider resistant organism.

STEC (E. coli O157:H7) / Shiga toxin-producing E. coli#

Education:

• Causes bloody diarrhea, often WITHOUT fever
• Associated with ground beef, unpasteurized products
• Can cause hemolytic uremic syndrome (HUS), especially in children and elderly
• DO NOT give antibiotics—increases HUS risk

Treatment:

• Supportive care ONLY
• IV fluids if needed (may be protective against HUS)
• NO antibiotics
• NO loperamide
• Monitor closely for HUS (days 5–10 after diarrhea onset)

HUS monitoring:

• Daily or every-other-day: CBC (hemoglobin, platelets), BMP (creatinine), urine output
• Signs of HUS: pallor, decreased urine output, petechiae, edema, altered mental status

Follow-up: Close monitoring for 2 weeks; daily contact for first week. If any signs of HUS → ED immediately.

Follow-up#

• Viral gastroenteritis: Return if not improving in 3 days or worsening
• Traveler’s diarrhea: Should improve within 24–48 hours of antibiotics
• C. diff: 3–5 days for clinical response; do NOT retest
• STEC: Close monitoring for HUS for 2 weeks

Return precautions (all patients):

• Bloody diarrhea (new or worsening)
• Fever >101.3°F (38.5°C)
• Unable to keep fluids down
• Signs of dehydration: dizziness, dark urine, no urination for 8+ hours
• Severe abdominal pain
• Not improving after 3 days

Patient instructions#

• Drink plenty of fluids to prevent dehydration. Take small, frequent sips of water, clear broth, or oral rehydration solutions.
• Avoid dairy products, caffeine, alcohol, and fatty or spicy foods until diarrhea resolves.
• Wash your hands thoroughly after using the bathroom to prevent spreading infection.
• You can return to work/school 24–48 hours after diarrhea stops (food handlers may need clearance).
• Take any prescribed antibiotics exactly as directed, even if you feel better.
• Do NOT take anti-diarrheal medications (like Imodium) if you have bloody diarrhea or fever unless your doctor says it’s okay.
• Call the office or go to the ER if you have bloody stool, high fever, severe pain, or signs of dehydration.

Smartphrase snippets#

.DIARRHEAACUTEVIRAL Acute diarrhea consistent with viral gastroenteritis. No red flags (no bloody stool, high fever, severe dehydration, or recent antibiotics). Plan: supportive care with oral rehydration, bland diet, loperamide PRN. No stool testing or antibiotics indicated. Discussed return precautions.

.DIARRHEAACUTEWORKUP Acute diarrhea with [bloody stool/fever/recent antibiotics/prolonged symptoms]. Ordered [stool culture/C. diff toxin/STEC testing/O&P]. Plan: supportive care pending results. [Started empiric antibiotics given severity / Holding antibiotics pending culture]. Discussed return precautions.

.CDIFF C. difficile infection confirmed. [First episode/recurrence]. Severity: [non-severe/severe]. Plan: oral vancomycin 125 mg QID x 10 days. Discussed stopping unnecessary antibiotics, avoiding loperamide, and contact precautions. Will NOT retest after treatment—clinical response is the goal.

Related pages#

• Diarrhea (Chronic) (complaint) — if symptoms persist >4 weeks
• Irritable Bowel Syndrome (problem) — post-infectious IBS can develop after acute gastroenteritis
• Abdominal Pain (Acute) (complaint) — if pain is prominent feature
• Nausea/Vomiting (complaint) — if vomiting is prominent