Whereas Nausea & Vomiting can be caused by disease in almost any part of the body, Diarrhea is always due to some problem in the small or large intestine. “Diarrhea” means watery or at least pretty loose stools.
We separate out our approach to diagnosis in terms of how long the symptom has been going on:
- less than 2 weeks = Acute Diarrhea
- over 1 month = Chronic Diarrhea
What about 2-4 weeks? We deal with it as acute, though only time will tell. Also, if the diarrhea has happened before, & keeps recurring, we’d consider it Chronic Diarrhea no matter how long it’s been going on this time.
On the other hand, it’s not unusual for Acute Diarrhea to be bad for a week, & then gradually tail off over 1-2 months. This may be due to temporary lactose intolerance caused by the germ that lived only briefly. Avoiding dairy products may help, but we don’t call it “chronic diarrhea” if it’s gradually getting better.
We also need to be sure the patient actually has diarrhea (loose or watery stools), & not anal discharge (that leaks out, may stain underpants). The latter would suggest STDs from anal sex.
Onward to Acute Diarrhea. Obviously, causes of chronic diarrhea begin acutely, but in the first 1-2 weeks of diarrhea, our Diagnosis is always: “due to Acute Gastroenteritis“ (i.e. a germ in the bowel).
Actually, “gastro” means stomach; viruses affect both stomach and bowel, bacteria that cause diarrhea are only in the bowel (bacteria in the stomach cause mainly vomiting, another topic). Anyway, that’s what we call it (see below for list of germs; see Acute Gastroenteritis for descriptions of them). Also see Differences Among Germs for a discussion of microbes in general.
Before going on, let’s wonder if Covid-19 can be a cause. Diarrhea is common with Covid, but very rarely as its only symptom. Diarrhea with nausea / vomiting might be due to Covid, and certainly if there’s fever, body aches, or cough. In such cases, many offices or clinics wouldn’t let the person inside, & would send them for a Covid test. But for now, we’ll think about diarrhea without considering Covid.
Regardless of the germ responsible, the most important thing we care about with Acute Diarrhea is whether the patient is Dehydrated. As long as there’s no vomiting, most adults & older children are able to drink enough fluids to stay hydrated. We worry about Dehydration if:
- Patient gets dizzy or almost faints after standing up
- Patient hasn’t urinated in 6-8 hours
If in doubt, we check postural vital signs (difference between lying down, & after standing up).
Once again, we want to know the diagnosis, i.e. the cause. Acute Diarrhea is undoubtedly caused by some germ. Sure, any disease causing ongoing Chronic Diarrhea starts on Day #1 as “Acute.” But that won’t make a difference in the beginning. For Acute Diarrhea, we only consider anything other condition besides germ-in-bowel in special cases:
- Sepsis (fatal blood infection)– Both Immunocompromised (weak immunity) and also with Fever are always at risk, and some diarrhea may occur with it. Still, even among those persons, Diarrhea is usually just a simple case of Gastroenteritis
- Bowel Ischemia (cut-off circulation, causing bowel death & gangrene) — Persons at risk include Elderly, & those with cardiovascular diseases. Causes Diarrhea + Abdominal Pain (usually severe) (see topic Abdominal Pain – Generalized)
- Anxiety — when acute, it can easily cause Acute Diarrhea
On to the germs — we get a hint by guessing if the diarrhea is from the small vs. large intestine:
- Small Intestine: stools are large volume and completely watery; non-bloody
- Large Intestine: frequent small-volume stools (squirts), with blood or mucus
Germs that Cause Acute Diarrhea (Gastroenteritis)
see Acute Gastroenteritis for descriptions of them
|xxxxxxSmall Intestine Germs |
• Other viruses
• Clostridium perfringens
• E. coli (Traveler’s diarrhea, other strains)
• Cryptosporidium *
• Microsporidium *
• Isospora *
|xxxxxxLarge Intestine Germs |
• Cytomegalovirus *
• E. coli (hemorrhagic)
• C. difficile
• Entamoeba histolytica (Amebic dysentery)
* = AIDS-related germs (Cryptosporidium also affects people with normal immune systems)
The overriding question we face for a patient with Acute Diarrhea is: do we order lab tests on stools? Since most acute diarrhea is caused by Viruses, for which there are no simple tests & no treatment, 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 the first 3-4 days of illness, we usually don’t order tests.
But in some situations, we do order a Stool Culture & Sensitivity for bacteria:
|• Bloody diarrhea|
• Significant abdominal pain
|• White cells in stool (not always checked)|
• Extreme diarrhea with dehydration
• Maybe food-handlers (if required by job)
Cultures identify the bacteria Salmonella, Shigella, and Campylobacter, sometimes Aeromonas. If the patient has diarrhea + sore throat, we suspect Yersinia (hard to find, so we’d alert the lab search for it as well).
If there’s bloody diarrhea and recent antibiotic use or hospitalization, we need a separate specimen for C. difficile.
In the medical literature, you can read about several types of E. coli (“E” stands for Escherichia), with such similar terminology that the abbreviations become awfully confusing:
- Enterotoxigenic E. coli (ETEC): Travelers’ diarrhea
- Enteropathogenic E. coli (EPEC): similar, but different strain
- Enteroaggregative E. coli (EAEC): similar, found in rich countries too
- Enteroinvasive E. coli (EIEC): invades colon, like Shigella
- Enterohemorrhagic E. coli (EHEC): toxin-producing
See what I mean?! And regular cultures can’t distinguish any of these strains from the plain old regular E. coli bacteria that live harmlessly in our healthy bowels & may constitute up to 4 lbs. of normal body weight. None of the diarrhea-causing strains require a different approach from other small- or large-bowel germs, except among returning travelers (see below), and cases of…
Enterohemorrhagic E. coli (EHEC). This was the “Jack-in-the-Box” 1993 bacteria from undercooked meat (also an Odwalla apple juice outbreak, & many other sources) which caused Hemolytic Uremic Syndrome (HUS), a life-threatening complication with anemia (“hemolytic”) and kidney failure (“uremic”). EHEC causes bloody diarrhea with abdominal tenderness and without fever. It can be detected by a special stool test for Shiga Toxin.
Unfortunately, antibiotics are associated with increased possibility of HUS, so they should never be given for bloody diarrhea without fever. The Shigella bacteria usually causes fever, and has its own dangers. So the presence or absence of fever determines whether we do or do not give antibiotics for bloody diarrhea while waiting for test results (both the stool culture, and also the special test for Shiga Toxin).
Salmonella is another problem. It can cause blood in stools, but antibiotic treatment doesn’t hasten cure and may prolong a carrier state (the germ stays in you). The bloody diarrhea from Salmonella is usually minimal, not like Shigella, Campylobacter, or EHEC.
By the way, it’s a bad habit to do tests for “occult blood” (blood we can’t see) with diarrhea, because the result tells us nothing (both false-positives and false-negatives!!!), & can lead to improper treatment. “Bloody diarrhea” as a reason to prescribe antibiotics should really mean “lots of visible blood.” Unfortunately, many clinicians still make decisions off tests for occult blood, which is simply wrong.
Listeriosis can include a self-limited diarrhea that gets better on its own. The bacteria is dangerous in pregnancy, but because it causes Sepsis and Meningitis, not because of the diarrhea. We worry about Listeriosis when a pregnant woman has fever, not just diarrhea. Routine stool cultures won’t even find the bacteria. To prevent serious complications of Listeriosis, pregnant women should avoid consuming unpasteurized dairy products, especially Mexican cheeses.
Parasites – Tests to detect protozoa are rarely useful. We have to obtain at least 3 specimens (testing for “Ova & Parasites“), each 24 hrs. apart, & will still miss some diagnoses. If we do order them, positive results are more likely when from diarrheal stools than semi-formed ones. AIDS-related germs are not detected on routine parasite tests. We have to order them separately.
Probably the best alternative to standard parasite tests is to order a single specimen for “Giardia antigen” (Giardia is the most common parasite to cause diarrhea). Some test kits can detect Cryptosporidium simultaneously. The difference between these tests & routine ones for parasites is that the lab test can find just a fragment of the germ, instead of searching for a live parasite or an entire egg manually by microscope. Results are usually faster as well.
We mostly consider tests for such Protozoa if there’s a history of:
- Traveled in Underdeveloped Countries: Giardia, Ameba, Cyclospora
- Travel to Russia: Giardia
- Wilderness hiking: Giardia
- Men-having-Sex-with-Men (MSM): Giardia, maybe Ameba
- Bloody Diarrhea + MSM, or + Traveled in Underdeveloped Countries: Ameba
- AIDS / severe immunocompromised: All possibilities (plus extra tests for AIDS parasites)
- Community Outbreak: Giardia, Cryptosporidium
Children >5 yrs. old with diarrhea are similar to adults, whereas causes in a younger child include non-infectious conditions such as ear or kidney infections, intussusception (collapsing of bowel), etc. But we do need worry about Hemolytic-Uremic Syndrome, and order kidney tests in all kids with bloody diarrhea (this website doesn’t address young children, due to author’s current lack of experience).
Travelers’ Diarrhea: Antibiotics may work for diarrhea if the patient had been traveling in poor countries within the last 2 weeks. Our usual treatment is Levofloxacin or Azithromycin 500 mg daily for 3 days. If the patient had been in poor parts of Asia, where E. coli bacteria are often resistant to that medication, treatment should be Azithromycin.
Anxiety can certainly cause acute diarrhea, especially acute anxiety. If you read All Quiet on the Western Front, you may remember how a new World War I German recruit, bravely eager for battle, pooped in his pants at the first cannonball. During El Salvador’s civil war, a woman I knew got diarrhea whenever she heard a nearby firefight. Unfortunately, that meant running outside (no indoor plumbing in poor rural huts), which increased the anxiety. Vicious cycle.
BEWARE – A dehydrated patient requires special caution. IV fluids in a clinic or ER can avoid 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 diagnosis is “gastroenteritis,” what’s the germ? What day of illness is it? Does the diagnosis fit with the normal course of illness?
- In the U.S., we should NEVER say “virus” if dehydration still persists after several days. See link for a Precautionary Tale.
TREATMENT — Though our Diagnosis123 doesn’t deal with treatment, a minor word about anti-diarrheal medications like loperamide (Imodium®) or Lomotil® that “stop up the bowel.” I rarely give them. The main treatment for diarrhea is, well, the Diarrhea itself (it’s the body’s way to get rid of germs)! When patients ask about such drugs, I say that they’re OK to take, “But if you stop up the bowel, germs stay inside longer.” And the drugs may sedate, so no driving, etc. Most people then decline.
- IMPORTANT: no anti-diarrheal meds for bloody diarrhea (may help bacteria work their way into the bloodstream)
See also Acute Diarrhea for the clinician’s condensed thought-process when face-to-face with a patient.