Infectious Diarrhea

Causes Include Viruses, Bacteria, and Parasites

Diarrhea is the second leading cause of death in children in the developing world and a major contributor to work absenteeism and loss of productivity in the American workforce.

The elderly, young children, and people with compromised immune systems are especially vulnerable and are at an increased risk of complications related to severe diarrhea including dehydration, the need for hospitalization and fluid management, and rarely even death.

Clostridium difficile Cell

Infectious vs. Non-Infectious Diarrhea

Viral, bacterial, and parasitic infections are the most common cause of diarrhea, and they are typically spread through the fecal-oral route. This occurs when an individual comes into contact with a contaminated surface (doorkob, button, counter top, or handshake) or by ingesting contaminated food or beverages.

There are also non-infectious reasons that a patient might develop diarrhea, and these are often related to medical conditions affecting the digestive, immune, or endocrine (hormone) systems. These conditions include irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), celiac disease, hyperthyroidism, and lactose intolerance.

The term gastroenteritis typically refers to bacterial of viral infections the affect both the stomach and small/large intestines. These patients present with nausea, vomiting, and abdominal pain, as well as diarrhea.

"Dysentery" refers to patients with infectious or inflammatory diarrheal diseases that result in the frequent passage of smaller stools containing varying amounts of mucus and/or blood.

Viral Causes

Viruses are the most common cause of diarrhea and are related predominately to four specific types:

  • Norovirus, also known as the "cruise ship virus," is the most common cause of food-borne gastroenteritis in the U.S.
  • Rotavirus is the most common cause of diarrhea in American children and a leading cause of death of children in the developing world.
  • Adenoviruses include a family of more than 50 subtypes. Types 40 and 41 are primarily responsible for causing diarrhea in humans. (Other adenoviral subtypes include cold viruses).
  • Astroviruses are common causes of diarrhea in the elderly, children, and people with compromised immune systems.

Bacterial Causes

Bacterial diarrhea is a major contributor to illness and death worldwide. Although less common in the U.S. than viral diarrhea, bacterial diarrhea disorders more often lead to dysenteric disease due to the development of ulcers and inflammation in the intestines. Among the most common causes:

  • Salmonella enteritidis can cause diarrhea, fever, and abdominal cramps within 12 to 72 hours of consuming contaminated food or beverage.
  • Escherichia coli (especially E. coli 0157) is spread through contaminated food and dairy products and can lead to a condition known as hemorrhagic colitis.
  • Shigella is common both in the U.S. and around the world and can often cause bloody diarrhea, particularly in children of preschool age.
  • Campylobacter is among the most common bacterial food-borne infections and can cause bloody diarrhea due to acute intestinal inflammation
  • Vibrio infection is often associated with eating raw seafood or sushi.
  • Staphylococcus aureus can cause explosive diarrhea due to toxins released by the bacteria.
  • Clostridium difficile is unique in that the rise of the infection is frequently linked to prior or concurrent antibiotic use. It is today the most common cause of hospital-acquired diarrhea.
  • Yersinia is a species of bacteria that can cause a number of different diseases in humans. Yersinia enterocollitica is a common cause of infectious diarrhea. In contrast, Yersinia pestis has been isololated as a primary cause of the bubonic plague. Humans typically encounter Yersinia species in dairy products.

Parasitic Causes

Protozoa are the primary cause of parasitic diarrhea both in the U.S. and around the world. These single-celled organisms come in many forms and are often transmitted through infected drinking water. Among the three most common causes of parasitic diarrhea:

  • Giardia lamblia is passed through contaminated food or by person-to-person contact and can result in explosive diarrhea within two days of infection.
  • Entamoeba histolytica is related to fecal-oral transmission and can cause bloody diarrhea as these invasive parasites bore their way into the intestinal wall.
  • Cryptosporidium is known to cause both respiratory and gastrointestinal illness and is characterized by the development of watery stools.

Diagnosis and Treatment

Based on the type of diarrhea experienced—as well as other symptoms and characteristics (including a person's travel history)—a doctor will run a series of tests to identify the source of the illness.

A stool culture is commonly used to diagnose bacterial infections, while a combination of microscopic and antigen-based tests can help identify protozoa in stool samples. Viral infections can be diagnosed by running a PCR test on a person's stool, blood, or other body fluids.

Treatment can vary based on the cause. Antibiotics and antivirals are typically used to treat bacterial and viral infections, respectively, while any number of antimicrobial agents may be used if the cause is protozoan.

In addition, anti-diarrheal medications may be prescribed along with oral rehydration therapy to prevent or treat the loss of fluid. Fluid can also be delivered intravenously (through a vein) if the dehydration is especially severe. Pain relief medications can help alleviate pain and fever.


An ounce of prevention is truly worth a pound of cure when it comes to avoiding infectious diarrhea. Chief among the prevention efforts is good hygiene and regular hand washing. While many people will invest in an antibacterial handwash, a thorough cleansing with hot water and soap will usually do the trick. Keeping sanitary conditions in the bathroom, kitchen, and anywhere where food is consumed is also key.

When cooking poultry, meat, or shellfish, make sure that they are thoroughly cooked and use a kitchen thermometer, if needed; these are useful to ensure that foods reach appropriate temperatures.Take extra care to wash all fruits and vegetables and avoid eating raw shellfish if you have any doubt about its origin or freshness. Cutting boards and utensils should also be cleaned immediately after coming into contact with raw meat, poultry, or seafood.

Finally, if traveling overseas, make sure your vaccinations are up to date. If planning to visit a developing country, visit the travel health website managed by the Centers for Disease Control and Prevention to learn which vaccinations are needed and to review any information related to water and local food safety.

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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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