Contributors:Aileen Lin, MScBMC, Alaina Mueller, Evan Debevec-McKenney, Filip Vasiljević, MD, Nancy Hutnik RN, BSN
Diarrhea is a condition where loose or watery stools are discharged from the intestines more frequently than normal, so more than three times in 24 hours. Now, based on its duration, diarrhea can be classified as acute, if it lasts for 2 weeks or less; persistent, if it lasts for more than 2 weeks but less than 30 days; and chronic if it lasts for more than 30 days.
Okay, let’s focus on the physiology of the intestines, which include the small intestine, as well as the large intestine or colon, and the rectum. The small intestine is the longest portion of the gastrointestinal tract, and it’s the main site for food digestion and absorption of most nutrients, such as amino acids, fatty acids, monosaccharides, vitamins, and minerals, as well as water.
The food that is not digested and absorbed travels to the large intestine, where the remaining nutrients and water are absorbed, and the stools are formed. From the large intestine, stools travel down to the rectum, and are eliminated from the body through the anus.
Moreover, the intestines contain a variety of non-pathogenic bacteria, which form the healthy intestinal flora, and aid with food digestion, as well as with the prevention of intestinal invasion by pathogenic bacteria and other microorganisms.
Now, based on the cause, diarrhea can be defined as infectious or non-infectious diarrhea. As its name implies, infectious diarrhea is caused by pathogenic microorganisms, which include: bacteria, most commonly Salmonella spp, and Shigella spp, as well as Escherichia coli, Vibrio cholerae, and Clostridioides difficile; as well as viruses, such as adenoviruses, norovirus, and rotavirus; and protozoa, such as Giardia lamblia and Entamoeba spp.
On the flip side, non-infectious diarrhea can be subdivided into three main groups. The first group is when diarrhea occurs as a side effect of medications that can disrupt the intestinal flora, such as antibiotics. The second group is food intolerance, like lactose intolerance; and finally, the third group includes underlying conditions, such as irritable bowel syndrome, Crohn disease, ulcerative colitis, and celiac disease.
However, not everyone who gets exposed to a causative agent will get diarrhea. Important risk factors for diarrhea include older age, living in or traveling to places with poor hygiene and sanitation, improper keeping and heating of food, poor water storage and handling practices, and living in overcrowded spaces.
Regardless of the cause, diarrhea occurs when there’s impairment of the normal intestinal absorption of water and nutrients, so diarrhea can also be classified into three major types, including inflammatory, fatty, and watery.
Inflammatory diarrhea occurs when there's damage to the intestinal mucosa due to inflammation, which can be caused by conditions like Crohn disease, or by food poisoning due to contamination by infectious microorganisms. Next, fatty diarrhea is specifically associated with impaired digestion and absorption of fats.
Finally, watery diarrhea occurs when water is abnormally secreted into the stools instead of being absorbed; watery diarrhea can be either osmotic or secretory. Osmotic diarrhea occurs due to an osmotic imbalance in the gastrointestinal tract, and it’s commonly seen in clients with lactose intolerance, who cannot digest lactose. As a result, lactose remains as an osmotically active compound, which attracts water molecules in the intestinal lumen and decreases their absorption, eventually causing diarrhea.
On the flip side, secretory diarrhea is typically caused by infectious microorganisms that secrete toxins, such as Escherichia coli or Vibrio cholerae, or medications, such as laxatives, which stimulate the secretion of water into the intestinal lumen; as well as conditions like diabetic neuropathy, which may alter gastrointestinal motility.
Now, the typical clinical manifestations of diarrhea include frequent, loose stools, often accompanied by abdominal pain and cramps, as well as urgency. Some clients may also experience bloating, nausea, vomiting, and weight loss; as well as fever, especially with infectious diarrhea. In some cases, the stools may have visible blood, mucus, or fat.
The main complication of diarrhea is dehydration, which can present with poor skin turgor and dry mucous membranes; and in severe cases, sunken-appearing eyes and delayed capillary refill. If not recognized in time, dehydration can eventually lead to electrolyte imbalance and metabolic acidosis, and can be life-threatening. Other severe complications of diarrhea include malnutrition, gastrointestinal perforation, sepsis, and even death.
The diagnosis of diarrhea is typically based on the client's history and physical assessment. Additionally, stool tests, such as a stool culture can be ordered to see if there’s an infectious microorganism; while the fecal osmotic gap can be measured in clients with watery diarrhea to determine if it’s osmotic or secretory.
The treatment of diarrhea is mostly supportive and includes oral rehydration and eating a low-fiber diet that’s easy to digest, including bananas, white rice,yogurt, applesauce, noodles, crackers, potatoes, boiled vegetables and soups. Some clients might require administration of glucose-electrolyte solutions, or even antidiarrheal medications, such as loperamide, which reduces the motility of the gastrointestinal tract, eventually reducing the frequency of stools.
It’s important to note that medications that reduce motility should not be used in infectious diarrhea, since their effect might delay the elimination of pathogens and toxins out of the gastrointestinal tract. Instead, these clients might require the administration of antimicrobials to fight the causative microorganism. Finally, clients can also take probiotics to help restore the intestinal flora, and for recurrent episodes of Clostriodiodes difficile diarrhea, fecal microbiota transplant can be helpful.