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, fecal-oral transmission from another individual, 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).

It typically causes an acute diarrhea that may occasionally be associated with fever, bloody stool, abdominal pain, and systemic symptoms.  Less commonly, a parasitic infection can cause chronic symptoms associated with malabsorption and weight loss.  Severe cases can result in sepsis and may be life-threatening.  Other conditions such as inflammatory bowel disease can have similar manifestations and must be considered.

What Causes Infectious Diarrhea?

It is caused by viruses, bacteria, or parasitic infections of the gastrointestinal tract.  Infections of the stomach or upper small intestinal often result in nausea and vomiting, whereas infection of the lower small intestine and colon (colitis) generally cause 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

How Common is Infectious Diarrhea?

It is relatively common in the United States and is often evaluated in the primary care clinic.  The condition may require referral to a gastroenterology specialist if symptoms are severe or first-line measures are unsuccessful.

Estimates show that there are about 1-3 infectious diarrhea illness per child per year.  Furthermore, there are approximately 76 million diarrheal illnesses per year, resulting in 350,000 hospitalizations, and 5,000 annual deaths.  In resource poor countries, the incidence of infectious diarrhea in individuals age >5 is about 30 episodes per 100 person-years in southeast Asia and 88 episodes per 100 person-years in the eastern Mediterranean.

Signs and Symptoms

Symptoms of infectious diarrhea often include:

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

Dysentery is characterized by:

  • Fever
  • Bloody diarrhea with mucous
  • Severe abdominal pain
  • Nausea & vomiting
  • Dehydration


The diagnosis is based on symptoms and physical examination, but is often confirmed with laboratory and occasionally imaging studies.  If you have mild symptoms without signs of dysentery, your doctor may not order any tests and will monitor your symptoms.  Many viral and bacterial forms of infectious diarrhea are self-limited and improve on their own.

If you have fever, bloody stool, or persistent symptoms your doctor will likely order stool tests such as white blood cell count, fecal occult blood test, ova and parasites, stool culture, and specific infectious antigen or 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 adequate hydration.  Patients with non-bloody diarrhea and 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).

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.

Traveler’s diarrhea often responds to fluoroquinolone antibiotics such as Cipro (ciprofloxacin) or macrolide antibiotics such as Zithromax (azithromycin).

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.