When Diarrhea Is Contagious: What To Know About Infectious Diarrhea

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

Generally speaking, diarrhea of any kind has a wide range of causes. Certain medicines, food intolerance, and 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 infectious diarrhea.

In the case of infectious diarrhea, the diarrhea is both infectious and contagious. Contagious diseases are spread by contact (usually person to person), while infectious diseases are spread by infectious agents. That means that, while diseases that are contagious are also infectious, not all infectious agents are necessarily contagious.

Specifically, infectious 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, told 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 to know if you have it, and what you can do to prevent and treat it.

What Causes Infectious Diarrhea?

Infectious diarrhea specifically is caused by one of three things: viruses, bacteria, or parasites.

Viruses

Viruses specifically are the most common cause of diarrhea that can be passed between people (e.g., 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

Norovirus, in particular, is notorious for diarrhea that's contagious—specifically on cruise ships (or other situations in which people live in close quarters), said Lisa Ganjhu, DO, a gastroenterologist at NYU Langone.

Bacteria

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

Parasites

Though they're less common than viral infections, the NIDDK says parasitic infections can cause some types of contagious diarrhea due to the following parasites:

• Cryptosporidium enteritis
• Entamoeba histolytica
• Giardia lamblia

How Can You Tell if You Have Diarrhea That's Contagious?

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. Acute diarrhea 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 said.

An acute case of diarrhea is something that "happens like once a year for most people," Dr. Ganjhu said. Because it's so infrequent, and most of us know how to deal with it, infectious diarrhea usually doesn't get diagnosed, Dr. Ganjhu added. If you do want to see a healthcare provider 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 said.

How Can You Treat Infectious 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 explained.

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 said.

Ways To Prevent Infectious Diarrhea

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 said. "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," Dr. Ganjhu added.

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 the water we consume in the US will most often be safe, there can still be danger in areas with sub-par sewer systems or after flooding or heavy storms, which can wash sewage into drinking water. In these situations, your city will send out a water boil alert, Christine Lee, MD, a gastroenterologist at the Cleveland Clinic, told Health. The Centers for Disease Control and Prevention (CDC) says that during a water boil advisory, you may be instructed to not only boil tap water but to use bottled water to avoid getting sick.

Ultimately, you'll want to keep in mind how easily infectious diarrhea spreads from person to person in order to avoid it or avoid giving it to someone else if you're already ill with it. "Diarrhea is probably one of the most communicable disorders out there," Dr. Ganjhu said.