Episode 227: Diarrhea

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• Acute is <2 weeks, persistent is 2–4 weeks, chronic is >30 days. Most acute diarrhea is self-limited and needs only supportive care.
• Stool cultures are positive in only 2–6% of unselected patients. Yield rises with >4 stools/day and longer duration.
• The ED job is not to name the organism. It is to find volume depletion, rule out the dangerous mimic, and decide who needs testing, antibiotics, or admission.

• Diarrhea is a symptom, not a diagnosis. In anyone who looks sick, gastroenteritis is a diagnosis of exclusion.
• Abdominal catastrophes: mesenteric ischemia (pain out of proportion, vascular risk factors), early appendicitis, partial obstruction with overflow stool, diverticulitis.
• Systemic disease presenting through the gut: sepsis from another source, DKA, adrenal insufficiency.
• Fulminant C. diff or toxic megacolon: distension, fever, tachycardia, peritonitis. The diarrhea may actually stop as the colon dilates.
• GI bleeding masquerading as dark diarrhea, and in women of childbearing age, ectopic pregnancy.

• Duration, frequency, and appearance. Watery and high-volume suggests small bowel. Small, painful, frequent stools suggest colon.
• Volume status: urine output, dark concentrated urine, dry mucous membranes, orthostatic symptoms.
• Exposures: recent foods, travel, sick contacts, occupation (animal or sewage contact), recent antibiotics or hospitalization.
• Timing after ingestion: <6 hours suggests a preformed toxin (Staph aureus, Bacillus cereus), 8–16 hours suggests Clostridium perfringens, and >16 hours suggests viral or other bacterial causes.
• High-risk hosts: pregnancy → Listeria, cirrhosis → Vibrio, hemochromatosis → Yersinia (both siderophilic).
• Exam: volume status plus a real abdominal exam. A soft belly does not end the evaluation.

• Ask first whether the result will change anything. If the patient is going home on supportive care, a stool study often just generates a callback.
• Test when the patient is likely to be admitted or is higher risk: febrile, hypovolemic, elderly (roughly >70), known cardiac disease, immunocompromised, IBD, or pregnant.
• Bloodwork is not routine. Send a BMP and CBC for significant hypovolemia, persistent vomiting, bloody stool, or the elderly and comorbid.
• Routine cultures cover Salmonella, Campylobacter, Shigella. Ask the lab specifically for Vibrio, Yersinia, Aeromonas, or Listeria.
• Know your multiplex GI PCR panel. At many shops it already includes C. diff, so ordering it separately is redundant. One call to your lab settles this.
• Bloody stool → send Shiga toxin. Bloody but fecal WBC negative → consider amoebiasis.
• Bloody diarrhea plus anemia, thrombocytopenia, or a rising creatinine → think HUS, especially in young children.
• Antibiotics or hospitalization within 3 months → C. diff moves up the differential.
• Neutropenic patient on active chemotherapy → consider typhlitis (enterocolitis of the cecum).
• CT only for peritoneal signs or focal tenderness. It is not part of the routine workup.

• Oral rehydration solution is the mainstay for anyone tolerating PO — water, salt, sugar. Preferred over sports drinks and flavored electrolyte powders, which are not ORS-formulated. A commercial ORS packet is ideal, and the home recipe works when you do not have one. One liter of water, six level teaspoons of sugar, half a teaspoon of salt.
• IV fluids for severe hypovolemia, intractable vomiting, or if labs are being drawn anyway.
• Most non-bloody, non-traveler’s diarrhea does not need antibiotics.
• Suspected Shiga toxin E. coli: no antibiotics. Lysing the organism releases toxin and raises HUS risk.
• When empiric coverage is warranted: azithromycin for severe inflammatory diarrhea, fever, dysentery risk, or fluoroquinolone resistance. Otherwise cipro or levofloxacin, and IV ceftriaxone if PO is not tolerated.
• Traveler’s diarrhea: most cases are self-limited. Reserve antibiotics for moderate to severe illness, and reach for azithromycin given widespread quinolone resistance in South and Southeast Asia.
• Confirmed C. diff: oral vancomycin 125 mg four times daily for 10 days, or fidaxomicin. Stop the inciting antibiotic where you can.
• Loperamide: generally avoid. If diarrhea is mild and the patient is afebrile, let it run.
• Bismuth subsalicylate is an option — avoid in younger patients (Reye’s syndrome) and in salicylate allergy or intolerance.
• Diet: eat what is tolerated. Early refeeding is fine and BRAT is not required. Dairy can transiently make things worse. Probiotics are unlikely to change the course.

• Set expectations: we often never identify the organism, and in a stable acute patient there is no routine test and no routine cure.
• Food handlers and healthcare workers may need occupational clearance before returning to work.
• Return precautions: bloody stools, fever, falling urine output, or an inability to keep fluids down.
• No improvement past 1–2 weeks warrants re-evaluation for parasitic or non-infectious causes, including IBD.

• Protozoan with no person-to-person spread — transmission is poop to produce to person. Humans are the only natural host.
• Oocysts need days to weeks to sporulate, so long-shelf-life produce is the culprit: berries, basil, cilantro, and leafy greens.
• Incubation is about a week. Presents as watery, explosive diarrhea, typically non-bloody and afebrile.
• Untreated, it drags on for weeks and tends to relapse, often with profound fatigue, anorexia, and weight loss.
• Included on many multiplex GI PCR panels. Microscopy requires a special stain or it will be missed.
• Treatment is Bactrim (TMP-SMX), one DS tablet twice daily for 7–10 days, which disrupts the parasite’s folate synthesis. Azithromycin does not cover Cyclospora — this is the exception to the usual workhorse. Ciprofloxacin is the fallback for sulfa allergy, and it is less effective.
• Washing produce does not kill it. Only heat does.

1. Most acute diarrhea is self-limited. If the patient tolerates PO, is afebrile, and the course is short, supportive care and discharge is the right answer.
2. Before you call it gastroenteritis, make sure it is not mesenteric ischemia, DKA, or a surgical abdomen.
3. Bloody diarrhea with concern for Shiga toxin gets no antibiotics.
4. For Cyclospora, wash and cook your produce — and remember it is Bactrim, not azithro.