Diarrhea – Acute

Diarrhea is much easier to address than nausea / vomiting, because now we know we’re dealing with the GI tract.  As always, define duration:

  • <2 weeks = Acute Diarrhea
  • >1 month = Chronic Diarrhea

What about 2-4 weeks?  It’s probably acute, though only time will tell.  Never forget our most important question of all (for any complaint): Is it getting better, getting worse, or staying the same?

And as usual, also establish chronology.  If the diarrhea’s been going on for a week, but the patient’s had prior similar episodes, consider it Chronic Diarrhea.  [Then ask how long each prior episode lasted, & you might get insight into today’s].

Also, be sure it’s diarrhea, & not anal discharge.  The latter would suggest STDs from anal sex.


As usual, we’ll touch on a bunch of interesting concepts (useful or not), & present a summary at the end.

Assess hydration as we discussed last posting; rehydration is the cornerstone of management.  But mostly, we want to know the diagnosis.  Acute Diarrhea is undoubtedly infectious.  I only ascribe Acute Diarrhea to anything else if:

  • Compromised host with fever — diarrhea may be non-specific component of Sepsis
  • Elderly patient with cardiovascular risks — diarrhea + Abdominal Pain (usually severe) may have Mesenteric Ischemia

History can often localize a pathogen to the small vs. large intestine:

  • Small Bowel: large volume, watery stools; non-bloody
  • Large Bowel: frequent small-volume stools, with blood / mucus


Small Intestine Pathogens

  • Norovirus
  • Rotavirus
  • Other viruses
  • Salmonella
  • Clostridium perfringens
  • E. coli (Traveler’s diarrhea, some other strains)
  • Aeromonas
  • Listeria
  • Cholera
  • Giardia
  • Cyclospora
  • Cryptosporidium *
  • Microsporidium *
  • Isospora *

Large Intestine Pathogens

  • Cytomegalovirus *
  • Shigella
  • Campylobacter
  • Yersinia
  • E. coli (invasive)
  • E. coli (hemorrhagic)
  • C. difficile
  • Entamoeba histolytica (cause of Amebic dysentery)

* = AIDS-related pathogens  (Cryptosporidium also affects immunocompetent persons)

The main clinical question we face is: do we order a work-up?  Since most acute diarrhea is viral, we usually don’t at first.  Norovirus symptoms persist up to 72 hours, although normal stools may not resume for a week or two.  Rotavirus lasts up to a week, adenovirus [uncommon] 12 days.  During in the first 3-4 days of illness, don’t pursue tests.

But some situations warrant a bacterial Stool Culture & Sensitivity:

  • Bloody diarrhea
  • Fever
  • Significant abdominal pain
  • Elderly
  • Stool wet prep positive for WBCs (if obtained)
  • Immunocompromised
  • Persistent, profuse diarrhea
  • Maybe food-handlers (if required by job)

Cultures identify Salmonella, Shigella, and Campylobacter, sometimes Aeromonas.  If the patient has diarrhea + pharyngitis, suspect Yersinia & request the lab search for it as well.  Same media, just harder to notice without advance warning.

If there’s a history of bloody diarrhea and recent antibiotic use or hospitalization, order a separate specimen for C. difficile.

In the literature, you’ll read about several types of E. coli, with such similar nomenclature that the abbreviations become awfully confusing:

  • Enterotoxigenic E. coli (ETEC): Travelers’ diarrhea
  • Enteropathogenic E. coli (EPEC): similar clinically, but different strain
  • Enteroaggregative E. coli (EAEC): similar clinically, found in developed world too
  • Enteroinvasive E. coli (EIEC): invades colon, like Shigella
  • Enterohemorrhagic E. coli (EHEC): toxin-producing

See what I mean?  And cultures can’t distinguish any of these strains from plain old non-pathogenic E. coli that colonize healthy bowel & may constitute up to 4 lbs. of normal body weight.  None require different management from other small- or large-bowel pathogens, except among travelers (while traveling), and cases of…

Enterohemorrhagic E. coli (EHEC), the “Jack-in-the-Box” 1993 culprit from undercooked meat (also an Odwalla apple juice outbreak, & many other sources); it presents a special problem.  It’s not found by culture, but rather a test for the O157:H7 strain, which produces Shiga toxins that cause Hemolytic Uremic Syndrome (HUS), with some mortality & 50% requiring temporary dialysis.  Since there are other EHEC culprit strains too, it’s best to test for Shiga Toxin 1 & 2 themselves, in addition to identifying actual strains for public health reasons.

Unfortunately, antibiotics increase the risk of HUS.  So do we give them pending results for possible Shigella / Campylobacter, or not?  The key is fever: EHEC causes bloody diarrhea and abdominal tenderness but without fever; patients with Shigella & Campylobacter are usually febrile.  So frequent small-volume bloody diarrhea and no fever means no antibiotics.

Salmonella is another confounder, because it can cause blood in stools, yet antibiotic treatment doesn’t hasten cure and may prolong carriage.  The blood is usually minimal, not overt like Shigella, Campylobacter, or EHEC.  A good reason NOT to do occult blood testing on diarrheal stools.  If using bloody diarrhea as a parameter for treating, stick with “grossly bloody.”

Listeria monocytogenes causes a self-limited diarrhea.  The bacteria is dangerous in pregnancy, but because of sepsis and meningitis, not gastroenteritis.  Don’t worry about Listeriosis in pregnant women with diarrhea; routine stool cultures even won’t identify it.  Worry more about counseling them to avoid unpasteurized dairy products, especially Mexican cheeses.

Ova and Parasites (O&P)  —  Tests to detect protozoa are rarely useful.  You have to obtain at least 3 specimens, each 24 hrs. apart, & you’ll still miss some diagnoses.  Diarrheal stools have better yield than semi-formed ones.

Note that AIDS-related pathogens are not detected on routine O&P’s.  You have to order them separately.

Probably the best alternative to O&P’s is to order a single stool specimen for Giardia antigen.  Some test kits can detect Cryptosporidium simultaneously.

Consider searching for Protozoa if you obtain a history of:

  • 3rd World Travel: Giardia, Ameba, Cyclospora
  • Travel to Russia:  Giardia
  • Wilderness hiking:  Giardia
  • Men-having-Sex-with-Men MSM):  Giardia
  • Bloody Diarrhea + 3rd World Travel or MSM:  Ameba
  • AIDS / severe immunocompromised:  All
  • Community Outbreak:  Giardia, Cryptosporidium

Children >5 yrs. old present similarly to adults.  Don’t worry about the causes you might in a younger child, such as otitis, UTI, intussuception, etc.  Do worry about Hemolytic-Uremic Syndrome; order BUN & Creatinine in kids with bloody diarrhea  (this Blog doesn’t address young children, due to author’s current lack of experience).

Anxiety as a cause of acute diarrhea — certainly possible, especially with acute anxiety.  During El Salvador’s civil war, a woman I knew got diarrhea every time she heard a gun-battle nearby.  Unfortunately, that meant running outside (no indoor plumbing in poor rural huts), which increased the anxiety.  Vicious cycle.


1.  Assess for, and manage, Dehydration
2.  Consider Stool Cultures as above
3.  Empiric Antibiotics for bloody diarrhea (while C&S pending)
4.  Bloody diarrhea: consider tests for C. difficile toxin, O157:H7 Shiga toxin
5.  Stool for C. difficile if recent antibiotic use + significant diarrhea
6.  Rarely need O&P (see above)

WORD OF CAUTION  —  Beware the dehydrated patient.  If you ever give IV fluids & the patient feels better, you’ve avoided a hospital admission.  But what’ll happen tomorrow (especially if it’s a weekend)?  Anybody that ill needs a diagnosis & close follow-up.

  • If the Dx is “gastroenteritis,” what’s the organism?  What day of illness is it?
  • In the U.S., NEVER say “virus” if dehydration still present after several days.

Though our DiagnosisDude doesn’t deal with treatment, a minor word about anti-motility agents.  I rarely give them.  The main treatment for diarrhea is, well, Diarrhea.  When patients ask about such drugs, I say that they’re OK to take, “But if you stop up the bowel, germs stay in there longer.”  And they may sedate, so no driving, etc.  Most people then decline.

Caveat: no anti-motility agents for bloody diarrhea (may promote invasion).

Next time — Chronic Diarrhea.

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