Ronald Strada Seminario

Diarrhea is defined as the expulsion of non-formed or abnormally liquid stools accompanied by a greater frequency in the evacuation rhythm. There are diverse criteria in the world for its definition, in the western hemisphere a quantity of feces greater than 200g per day can be considered as diarrhea.

Acute diarrhea is a cause of high morbidity and mortality in developing countries, especially in children, the elderly, and immunosuppressed.


Types of diarrhea


Characteristics and composition



Presence of non-absorbable or poorly absorbable solutes in the intestinal lumen

  • Volume less than 1000 ml / day
  • Decreases with fasting.
  • Osmolar GAP greater than 100
  • Lactose intolerance
  • Excessive intake of sorbitol


Alterations of the hydroelectrolytic transport through the mucosa 

  • Volume greater than 1000 ml / day
  • Does not change with fasting
  • GAP osmolar less than 50
  • Enteropathogenic Escherichia coli
  • Adenoma velloso
  • Anger
  • Medullary thyroid carcinoma
  • Zollinger-Ellison syndrome


Increased speed of intestinal transit 

  • Variable
  • Irritable bowel syndrome
  • Hyperthyroidism 

Inhibition of normal absorption mechanisms 

Chlorine is not absorbed 

  • Increased excretion of chlorine
  • Decreases with fasting 
  • Acute viral diarrhea
  • Congenital hydrochloride 

In general, to calculate the osmolar gap, it is recommended to use a standard value (290) that is the osmolarity of faeces in the distal intestine, in equilibrium with plasma osmolarity. The osmolar gap is calculated by subtracting the fecal osmolarity from the sum of (Na and K fecal) x2. In osmotic diarrhea, the osmolar gap is usually greater than 100, due to osmotically active and poorly absorbable substances in the faeces. In secretory diarrhea, fecal osmolarity is similar to plasma osmolarity, for this reason the osmolar gap is less than 50.

Classification according to the characteristics of the stool

In osmotic and secretory diarrhea, faeces are generally watery and abundant. In malabsorption (celiac disease, for example), the stool is steatorrheic (smelly, foul, and floats due to the abnormally high amount of fat). Inflammatory diarrhea is one that is accompanied by mucus, pus, and blood. Diarrhea with a large amount of mucus can be seen in patients with hairy tumors.

Classification according to time of evolution

Acute diarrhea is defined as diarrhea that lasts for a period of up to 2 weeks. Prolonged diarrhea is that diarrhea that lasts between two weeks and a month.

Chronic diarrhea defines those symptoms that last longer than a month.

Acute diarrhea

Approximately 90% of acute diarrhea is due to infectious agents.

Infectious diarrheas: They are transmitted by the oral faecal route, person to person and / or by ingesting contaminated food and water.

Most episodes of acute diarrhea are self-limiting and do not require additional studies.

However, the study of the cause of diarrhea should be performed when there is dehydration, blood in the stool, fever of 38.5 or more, profuse diarrhea for more than 48 hours, severe abdominal pain and in immunosuppressed patients (HIV, transplant patients , elderly patients, etc.)

The risk of getting gastroenteritis varies depending on age and risk groups. Housing type, population density, living conditions, personal habits, and water sources are determinants of environmental exposure to enteric pathogens.

Infants and children are more prone to infection with rotavirus, Campylobacter Jejuni, Shigella, and Salmonella spp. However, older children are more frequently infected with Norwalk-type viruses.

Escherichia Coli produces a thermolabile (LT) or thermostable (ST) enterotoxin that causes disease in the tropics. Between 20 to 50% of travelers traveling from temperate to tropical areas will have traveler's diarrhea. This pathology is generally due to the ingestion of contaminated food or water and generally tends to limit itself between 1 to 5 days. The most common cause of traveler's diarrhea is enterotoxic Escherichia Coli, with Shigella, Campylobacter Jejuni and Vibrio Cholerae also being causes of traveler's diarrhea. Traveler's diarrhea of ​​parasitic etiology includes Entamoeba Histolytica and Giardia Lamblia.

Gastrointestinal infections are also frequent in hospitals, health institutions and day centers and are generally caused by Clostridium Difficile and Salmonella.


The most important defense mechanisms of the host are cellular and humoral immunity, saprophytic flora, gastric pH and peristalsis.

Immunity: In the lamina propria of the small intestine (Peyer's patches) and in the colon, there are lymphoid cells that are arranged in nodules and that play an important role in defense against enteropathogenic bacteria.

Humoral immunity, through the secretion of immunoglobulins, also plays an important protective role.

Various components of mucus and intestinal secretions such as lysozyme and lactoferrin contribute to reducing the pathogenic bacterial population of the colon. In the infant, an additional protection mechanism is lactoferrin from breast milk, which, when joined to iron, produces a bacteriostatic effect.

Saprophytic flora: 99% of the saprophytic intestinal flora, located mainly in the last section of the small intestine and in the colon, is predominantly made up of anaerobic microorganisms and prevents the colonization of enteropathogenic bacteria. It is a natural immunity mechanism. In children who have not yet developed normal enteric colonization, or after taking antibiotics, enteropathogenic microorganisms can cause infection with smaller inocula.

Peristalsis: Gastrointestinal motility is also an important mechanism for getting rid of microorganisms. Motility disorders such as those that exist in diabetes or scleroderma favor colonization of enteropathogenic bacteria

Heartburn: pH below 4 destroys most ingested bacteria. Situations of hypo or achlorhydria carry an increased risk of enteric infections.

The microbial factors that influence are the size of the infectious inoculum, the adhesion capacity, the production of toxins and the capacity of the infectious agent to invade the intestinal cells.

Acute infectious gastroenteritis

Food poisoning

They generally have a short incubation period (12 to 24 hours approximately).

They are due to the ingestion of enterotoxins produced outside the host in some foods (mayonnaise, eggs, beef, cheese, salads, etc.)

They cause nausea, vomiting and abdominal pain, the most frequent causes being Salmonella spp, Stafilococo aureus, Bacilus cereus, Clostridium perfringens and Clostridium botulinum.

Invasive infections

When the causative agent is invasive, the incubation period and the duration of the disease are usually longer than those caused by toxins.

The clinical picture is acute dysentery, characterized by fever, diarrhea, abdominal pain, and rectal tenesmus. Shigella, Salmonella, Campylobacter, enteroinvasive Escherichia coli, and Yersinia enterocolitica are the most frequent causative agents.

Some of these microorganisms can produce extraintestinal pathology such as bacteremia, migratory polyarthritis, erythema nodosum and Guillain Barré syndrome. Yersinia enterocolitica produces a picture of mesenteric adenitis that simulates acute appendicitis, with intense pain in the right iliac fossa; Another complication in children is hemolytic uremic syndrome associated with Shigella and enterohemorrhagic Escherichia Coli.

Listeria is increasingly recognized as a cause of gastroenterocolitis with a high percentage of mortality (20%) complicating endocarditis or meningitis.

Pseudmomembranous colitis is caused by Clostridium difficile, with antibiotic intake, prolonged hospitalizations, and advanced age being risk factors for developing it.

Food poisoning


Symptoms and signs 



1 to 6 hours incubation

S. Aureus 

Nausea, vomiting, and diarrhea

Ham, potatoes, egg, mayonnaise, cream pastes


B. Cereus 

Nausea, vomiting, and diarrhea

Fried rice 


8 to 16 hours incubation    

C. Perfringes 

Abdominal pain, diarrhea (rarely vomiting)

Beef, pulses


B. Cereus 

Abdominal pain, diarrhea (rarely vomiting) 

Beef, vegetables, cereals 


incubation over 16 hours    

Vibrio Cholerae 

Liquid diarrhea 



E. Coli enterotoxigenic 

Liquid diarrhea 

Salads, cheese, beef, water


Salmonella spp. 

Inflammatory diarrhea

Beef, eggs, dairy 


Shigelle spp. 


Potatoes, lettuce, raw vegetables 


Vibrio parahaemolyticus 



10% of acute diarrhea is due to medications, the most frequent causes being the intake of certain antibiotics that produce dysbacteriosis, antiarrhythmics, nonsteroidal anti-inflammatory drugs, ischemic colitis, etc.

Chronic diarrhea


  • Laxative use
  • Chronic intake of ethanol
  • Ablations
  • Radiation enteritis
  • Fistulas
  • Partial obstruction or fecal impaction
  • Tumors (Vipoma, Zollinger Ellison syndrome, carcinoid, pheochromocytoma medullary thyroid carcinoma)
  • Adenoma tubulovelloso
  • Colonic adenocarcinoma
  • Adisson disease
  • Birth defects of electrolyte absorption
  • Osmotic diarrhea (lactase deficiency, sorbitol intake, etc.)
  • Exogenous pancreatic insufficiency
  • Celiac Disease
  • Whipple's disease
  • Ulcerative colitis
  • Ischemia
  • Diabetes
  • Crohn's disease
  • Collagenous / microscopic colitis
  • Mucosal immune disorders
  • Infiltrative diseases (amyloidosis, lymphoma)
  • Viral, bacterial, and parasitic infections
  • Miopatías
  • Short bowel syndrome
  • Hyperthyroidism
  • Bulimia
  • Chronic renal insufficiency
  • Bacterial overgrowth
  • Irritable bowel syndrome

The most frequent etiological agents causing chronic diarrhea are parasites (Giardia Lamblia, Oxiurus, Ascaris, etc.)

Chronic diarrhea that does not affect the general state is usually the manifestation of a functional disease, the most frequent being irritable bowel syndrome. It is characterized by abdominal pain, bloating, and changes in bowel movements, without weight loss and without bleeding.

Any dietary change, intake of vitamin supplements, and new medication can cause diarrhea.

A history of a cholecystectomy can result in bile salt diarrhea, usually temporary.

The history of the use of antibiotics within the six months prior to the consultation requires that Clostridium difficile be ruled out. The diagnosis is made by searching for specific toxins and performing a video colonoscopy in which characteristic whitish plaques are observed.

In the population older than 50 years, the appearance of diarrhea with loss of weight and / or blood in the stool should be considered an accurate indication for performing a video colonoscopy.

Celiac disease is an important cause of chronic diarrhea, although it is not uncommon for some patients to debut with constipation. It can be accompanied by anemia, menstrual disorders, a history of abortion or infertility in women, osteopenia and growth disorders in children and adolescents. It is diagnosed with biopsies of the small intestine or with detection of specific antibodies.

Inflammatory bowel diseases (ulcerative colitis and Crohn's disease) are chronic diseases that produce chronic diarrhea, abdominal pain and alteration of the general state. Ulcerative colitis has diarrheal stools with pus mucus and blood. Crohn's disease can affect the small intestine, the colon or both accompanied or not by anorectal pathology. It is characterized by abdominal pain generally focused on the right iliac fossa, diarrhea and weight loss.

Bacterial overgrowth is characterized by diarrhea, weight loss, malabsorption, bloating, and meteorism. It is more frequent in patients with diabetes and in pathologies that affect visceral motility.

Less frequent causes of chronic diarrhea are Whipple's disease, amyloidosis, tuberculosis, etc.


A careful physical examination should be performed looking for signs of chronic disease, weight loss, stigmata of chronic liver disease, hepatosplenomegaly and palpable intra-abdominal masses.

The laboratory examination must include leukocytes in fecal matter. Their presence suggests an inflammatory disease that should be ruled out by video colonoscopy.

In cases of chronic diarrhea, the colon must be biopsied to rule out collagenous or microscopic colitis, the diagnosis of which is pathological.

The collection of fecal matter for the determination of Na and K is useful to calculate the osmolar gap. In cases where suspicious consumption of laxatives is suspected, it is common to find an increase in the concentration of magnesium in fecal matter. A complete blood laboratory will be performed (hemogram, iron profile, glycemia, electrophoresis proteinogram, hepatogram, erythrocyte sedimentation), stool cultures, occult blood and physical-chemical examinations of fecal matter (volume, pH, etc.).

The search for Giardia should be carried out since this is a very frequent parasitic infection that causes chronic diarrhea, bloating and meteorism.

The history of alcoholism should suggest pancreatic insufficiency.

Abdominal ultrasound: it is convenient to perform it because it is not an invasive method and can provide useful information for diagnosis.

Endoscópic Studies and contrast Thomografies should be considerar on  case by case bases