Diarrhea – Diagnosis, Symptoms, and Treatment

Doctor Nathan LeDeaux, MD

Medically reviewed by Dr. Nathan LeDeaux, MD

Medical Professional

Updated - December 28, 2020

Nathan LeDeaux is an emergency medicine physician at the University of Wisconsin and got his M.D. from Northwestern University in Chicago Illinois.

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What is Infectious Diarrhea?

Infectious diarrhea is a medical term for diarrhea caused by an infectious organism – these typically include viruses, bacteria, and occasionally parasites.  Patients may develop this condition through food contamination, accidental ingestion of fecal material from another individual - typically through drinking water, drinking out of streams, antibiotic use, and hospitalization.  Individuals also frequently acquire infectious diarrhea or gastroenteritis by traveling to resource-poor countries (traveler’s diarrhea).

Infectious diarrhea generally presents as acute watery diarrhea that may be associated with fever, bloody stool, and abdominal pain.  Less commonly, a parasitic infection can cause chronic symptoms that present with malabsorption and weight loss. Severe cases can result in sepsis, an infection that spreads to all areas of the body, becoming potnetially life-threatening.  Other conditions such as inflammatory bowel disease can have similar manifestations to infectious diarrhea and must be considered.

What Causes Infectious Diarrhea?

Infectious diarrhea can be caused by viruses, bacteria, or parasitic infections of the gastrointestinal tract.  Infections of the stomach or upper small intestine often result in nausea and vomiting, whereas infection of the lower small intestine and colon generally causes diarrhea.

Common viruses responsible for diarrhea consist of:

  • Rota virus
  • Influenza virus
  • Adenovirus
  • Cytomegalovirus (CMV)
  • Human immunodeficiency virus (HIV)

Common bacteria responsible for diarrhea include:

  • Bacillus cereus
  • Staphylococcus aureus
  • Campylobacter
  • Shigella
  • Salmonella
  • Enterohemorrhagic coli
  • Enteroinvasive coli
  • Clostridium difficile

Parasites that are implicated in infectious diarrhea include:

  • Giardia lamblia
  • Entamoeba
  • Cryptosporidium
  • Microspora

The viruses that cause diarrhea almost all cause a classic watery diarrhea that is associated with nausea and vomiting. The bacteria and parasites cause a far more diverse set of symptoms and are the cause of severe cases.

How Common is Infectious Diarrhea?

Infectious diarrhea is relatively common in the United States. Viral causes are far more common and mainly occur in children. It is estimated that 1 to 3 episodes of infectious diarrhea occur per child in the US per year. 

In addition to the cases in young children, an estimated 76 million cases of infectious diarrhea occur in the United States each year. The more severe cases occur in the very young and very old. These lead to 350,000 hospitalizations per year and about 5,000 deaths. The number of cases and deaths from infectious diarrhea is much higher in resource-poor countries. 


Signs and Symptoms

Almost all cases of infectious diarrhea result in the following symptoms. 

  • Malaise
  • Nausea & vomiting
  • Water & non-bloody stool
  • Mild abdominal discomfort

More severe parasitic and bacterial infections result in a group of symptoms that are often referred to as dysentery. These symptoms generally progress over the course of days, starting with the more mild symptoms listed above and progressing to the following:

  • Fever
  • Bloody diarrhea with mucous
  • Severe abdominal pain
  • Dehydration


The diagnosis of infectious diarrhea is based on your history of symptoms and any potential exposures to organisms that can cause diarrhea. If you have mild symptoms few to no studies will be needed and you will be asked to monitor your symptoms and return to the office if more severe symptoms develop. The more mild cases of infectious diarrhea will resolve without treatment.

If you have more severe symptoms such as fever, bloody stool, or persistent symptoms that last for several days your doctor will likely order stool tests such as white blood cell count, fecal occult blood test, stool ova and parasites, a stool culture, and tests for specific pathogens known as PCR tests.  They may even refer you to a gastroenterologist to undergo colonoscopy.  Cases accompanied by severe abdominal pain may require a CT scan of the abdomen.

Commonly ordered blood tests include a CMP (comprehensive metabolic panel), CBC (complete blood cell count), thyroid function (TSH, free T4), and coagulation studies (PT/INR, PTT).

Infectious Diarrhea Medication and Treatment

Mild cases of infectious diarrhea are typically treated with rest and adequate fluid intake.  Patients are typically encouraged to drink fluids that contain solutes and carbohydrates to ensure that electrolytes lost in diarrhea do not result in severe electrolyte deficiencies.  Patients with non-bloody diarrhea and the absence of fever may benefit from antidiarrheal medications such as Imodium (loperamide) as needed.  Those with nausea may benefit from antiemetics such as Reglan (metoclopramide) or Zofran (ondansetron). These medications should not be used in patients with severe bloody diarrhea as it may worsen the infection resulting in bloody diarrhea. 

Viral infections typically do not have a specific antimicrobial therapy.  Treatment is normally supportive with fluids, Tylenol (acetaminophen) for fever or body aches, and Imodium (loperamide) as needed.

Certain bacterial forms of diarrhea such as Clostridium difficile require treatment with antibiotics.  This typically includes Flagyl (metronidazole) or occasionally Vancocin(oral vancomycin) in those with recurrent C. difficile infection. Infections caused by these bacteria generally only occur in those that have recently been admitted to a hospital or a nursing home. 

Traveler’s diarrhea in those visiting resource-poor countries often responds to fluoroquinolone antibiotics such as Cipro (ciprofloxacin) or macrolide antibiotics such as Zithromax (azithromycin). The best treatment for this form of diarrhea is prevention. Avoiding uncooked foods, tap water, and ice can help prevent exposure to the bacteria that commonly cause travelers diarrhea. 

Parasitic infections are typically treated with Flagyl (metronidazole) or sometimes Albenza (albendazole).


  1. Guerrant RL, Van Gilder T, Steiner TS, et al. Practice guidelines for the management of infectious diarrhea. Clin Infect Dis 2001; 32:331. - https://www.ncbi.nlm.nih.gov/pubmed/11170940
  2. Musher DM, Musher BL. Contagious acute gastrointestinal infections. N Engl J Med 2004; 351:2417. -https://www.nejm.org/doi/full/10.1056/nejmra041837
  3. Bresee JS, Marcus R, Venezia RA, et al. The etiology of severe acute gastroenteritis among adults visiting emergency departments in the United States. J Infect Dis 2012; 205:1374. - https://www.ncbi.nlm.nih.gov/pubmed/22454468


Diarrhea Medication

The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.