Is Diarrhea Contagious? Here's What to Know About Infectious Diarrhea, According to Gastroenterologists

Not all cases of diarrhea can be passed from person to person—but many of the main causes of diarrhea are contagious.

Unpleasant as it is, diarrhea—that loose, watery stool—is a common and normal part of life. Diarrhea is technically characterized as having a loose bowel movement three or more times in one day, according to the US National Library of Medicine (MedlinePlus), and it can be chronic or acute.

Generally speaking, diarrhea of any kind can be caused by a wide range of things. Certain medicines, food intolerance, chronic diseases are all things that can cause chronic, non-infectious diarrhea. But acute diarrhea specifically—the kind that comes on quickly and lasts up to a few days—is usually contagious, meaning you picked it up from contact with another person who also had diarrhea.

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How that happens is unnerving, to say the least: Contagious diarrhea usually makes its way into your body through what's known as fecal-oral transmission, Carolyn Newberry, MD, a gastroenterologist at Weill Cornell Medicine, tells Health. That means, technically, the infectious agent is shed in the stool of another host or person, and somehow enters the mouth of the next host or person.

Here, gastroenterologists help explain when diarrhea is contagious, how you know if you have contagious diarrhea, and what you can do to prevent and treat it.

When is diarrhea contagious—and what causes it?

Let's dial it back a bit here: Infectious diarrhea specifically is caused by one of three things: bacteria, viruses, or parasites. Though the words "contagious" and "infectious" may often be used interchangeably, they're not exactly the same thing. Contagious diseases are spread by contact (usually person to person), while infectious diseases are spread by infectious agents. That means, while diseases that are contagious are also infectious, not all infectious agents are necessarily contagious.

Viruses specifically are the most common cause of diarrhea that can be passed between people (think: when someone neglects to wash their hands after using the bathroom and then touches a commonly-used surface). According to MedlinePlus and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), the most common viruses that can cause diarrhea include:

  • Norovirus
  • Rotavirus (in children)
  • Influenza

Of course, that's not an exhaustive list of viral causes of diarrhea. According to the Mayo Clinic, adenoviruses, astrovirus, cytomegalovirus, and viral hepatitis are also known causes of diarrhea. Norovirus in particular is notorious for contagious diarrhea—specifically on cruise ships (or other situations in which people live in close quarters), says Lisa Ganjhu, DO, a gastroenterologist at NYU Langone.

Bacteria, too, can cause diarrhea. While many types of bacteria that cause infectious diarrhea stem from ingesting contaminated food, it is possible for people infected with the bacteria to spread it to others. According to the NIDDK, the most common types of bacteria that can cause diarrhea include:

  • Campylobacter
  • Escherichia coli (E. coli)
  • Salmonella
  • Shigella

Parasitic infections can also be the root cause of some cases of contagious diarrhea. Though they're a less common that viral infections, the NIDDK says the following parasites that can cause contagious diarrhea include:

  • Cryptosporidium enteritis
  • Entamoeba histolytica
  • Giardia lamblia

How can you tell if you have contagious diarrhea?

Obviously, not all instances of diarrhea are contagious. Most often, when diarrhea is chronic or lasts for an extended period of time, it's indicative of underlying issues or diseases like irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), food intolerances, or medications.

In that case, the biggest indicator that your diarrhea is contagious is that it comes on quickly, rather than being an expected part of your life. Acute diarrhea, as it's called, is almost always contagious. "So things like that can clue you in — it comes on all of a sudden, you've been around someone sick, recently traveled, or ate spoiled food," Dr. Newberry says.

An acute case of diarrhea is something that "happens like once a year for most people," Dr. Ganjhu says. Because it's so infrequent, and most of us know how to deal with it, contagious diarrhea usually doesn't get diagnosed, she says. If you do want to see a doctor for your diarrhea, however, they'll be able to tell whether it's caused by parasites, bacteria, or a virus through a simple stool test. "There are a lot of different bugs we can actually test for," Dr. Ganjhu says.

How can you treat (and prevent) contagious diarrhea?

Although you might not have known it, you've almost certainly had contagious diarrhea before and already know how to treat it: with lots of fluids and rest. "If you have a healthy immune system, you'll be sick for a few days and it will clear up on its own," Dr. Newberry says.

To help you get through a bout of acute diarrhea, stick to foods that are gentle on your stomach and drink lots of water and something with minerals (like sports drinks or enhanced waters) to replenish electrolytes. If you need it, you can also use an over-the-counter medicine like Pepto Bismol to calm your stomach. "Just let your body fight the infection off," Dr. Newberry says.

As for avoiding contagious diarrhea (or avoiding giving it to someone else if you're already ill with it), keep in mind how easily is spreads from person to person. "Diarrhea is probably one of the most communicable disorders out there" says Dr. Ganjhu.

To protect yourself (or others), you'll want to keep your distance, avoid touching commonly-used surfaces, and wash or sanitize your hands when necessary. If you share a space with someone who has a bacterial form of diarrhea specifically, make sure you sanitize or disinfect surfaces as much as possible, Dr. Ganjhu says. "It's very important that if that person uses the toilet to make sure you bleach down all the surfaces to kill any potential cross contamination," she says.

However, because diarrhea-causing bacteria and parasites are also often found in contaminated food and water, it's important to know how to avoid that contamination. That means making sure to cook poultry, meat, or shellfish all the way through before eating; and abiding by other food-safety practices, like keeping perishable items refrigerated, and properly washing all fruits and vegetables.

And while, most often, the water we consume in the US will be safe, there can still be danger in areas with sub-par sewer systems or after flooding or heavy storms, which can wash sewer into drinking water (in these situations your city will send out a water boil alert, Christine Lee, MD, a gastroenterologist at the Cleveland Clinic, tells Health).

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