Diarrhea can be caused by many conditions. Some types of diarrhea are contagious and can be spread between people and even from animals to people. Diarrhea can also be a symptom of a disease that is not infectious.

For healthy people, occasional diarrhea usually doesn't last long and gets better on its own without causing major problems. However, diarrhea is the second leading cause of death in children in the developing world. It's also a major contributor to work absenteeism and loss of productivity in the United States' workforce.

The elderly, very young children, and people with compromised immune systems are especially vulnerable to diarrheal infections. They are at an increased risk of complications related to severe diarrhea including dehydration and the need for hospitalization and fluid management. They may also be more likely to die from these complications.

This article will go over the types of diarrhea, the causes of diarrhea, how to tell if diarrhea is contagious, and how long infectious diarrhea usually lasts. You will also learn about infectious diarrhea treatments and how to prevent diarrhea.

Infectious vs. Non-Infectious Diarrhea

Diarrhea can be contagious but it is not always. To find out if a case of diarrhea is infectious or not, you'll need to see a healthcare provider.

What is considered infectious diarrhea, how long infectious diarrhea lasts, and what can be done to treat and prevent diarrhea caused by infections depends on the cause.

Infectious Diarrhea

The most common causes of diarrhea are viral, bacterial, and parasitic infections. Infectious diarrheal diseases are contagious, meaning that they can be spread between people.

Diarrheal infections are typically spread through the fecal-oral route. This means that fecal matter that has infectious particles in it gets on a surface or person. Things that people touch a lot, like doorknobs, buttons, and counters can be easily contaminated.

If people don't wash their hands after they use the bathroom, they can spread the infection when they touch other people (for example, by shaking hands). People can also catch infections that cause diarrhea if a sick person makes food for them.

Kids often spread infectious diarrhea easily because they tend to put their hands and objects in their mouths.

Animals can also contaminate sources of water and surfaces with pathogens that spread infectious diarrhea. These illnesses can also be transmitted if people don't wash their hands after touching an animal.

Infectious diarrhea often comes quickly and does not last longer than a few days, though some illnesses may cause diarrhea that lasts a week or two.

Once the cause is found, most infectious diarrheal diseases can be treated. However, some types of infectious diarrhea are harder to treat. People may have diarrhea that lasts a long time and leads to complications.

Viral Causes

Viruses are the most common cause of diarrhea. There are four specific viruses that most often cause infectious diarrhea:

• 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 in 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 a common cause of diarrhea in the elderly, children, and people with compromised immune systems.

Infectious diarrhea caused by a virus is usually highly contagious.

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. The bacteria that commonly cause infectious diarrheal disease include:

• 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 foodborne 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 isolated as a primary cause of the bubonic plague. Humans typically encounter Yersinia species in dairy products.

Bacterial infections that cause diarrhea can spread quickly between people, but it's more common for people to get sick after drinking water or eating food that is contaminated.

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. 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.

Infectious diarrhea caused by parasites is usually transmitted through infected drinking water.

Non-Infectious Diarrhea

Diarrhea can also be non-infectious. People with medical conditions affecting the digestive, immune, or endocrine (hormone) systems can have diarrhea as a symptom. Diarrhea caused by these conditions cannot be spread to other people.

Medical conditions that can cause non-infectious diarrhea include:

• Irritable bowel syndrome (IBS)
• Inflammatory bowel disease (IBD)
• Celiac disease
• Hyperthyroidism
• Lactose intolerance

People with these conditions may have acute episodes of diarrhea when the disease flares up, or they may have chronic diarrhea that lasts a long time.

Diagnosis and Treatment

You may not be able to tell if diarrhea is contagious or not based on how you feel. The symptoms of infectious diarrhea can be similar to non-infectious diarrhea. If you have an infection that's causing diarrhea, you won't necessarily know which pathogen is causing it.

Diagnosing Diarrhea

To diagnose infectious diarrhea, providers will gather information from a patient—for example, if they have been around sick people or traveled recently. They can also run a series of tests to identify the cause of diarrhea.

Finding out whether diarrhea is infectious or not has several steps:

• A stool culture is commonly used to diagnose bacterial infections
• 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

Diarrhea Treatment Guidelines

The treatment for diarrhea depends on the cause and how sick a person is.

For infectious diarrheal diseases, there are medications that can be given. For example, antibiotics and antivirals can treat bacterial and viral infections, respectively, while antimicrobial agents can treat diarrhea caused by protozoans.

Anti-diarrheal medications can be prescribed along with oral rehydration therapy to prevent or treat the loss of fluid from diarrhea. The fluid can also be delivered intravenously (through a vein) if the dehydration is especially severe.

You may have a fever with infectious diarrhea. If you have a fever and feel sick when you have diarrhea, an over-the-counter (OTC) fever-reducing or pain-relieving medication may help.

Prevention

An ounce of prevention is truly worth a pound of cure when it comes to avoiding diarrhea. Here are a few tips for preventing diarrhea infections at home and while you're out:

• Practice frequent proper handwashing with hot water and soap or use an antibacterial handwash,
• Sanitize your bathroom, kitchen, and anywhere in your home where food is prepared and eaten
• Thoroughly cook all poultry, meat, or shellfish and use a kitchen thermometer to ensure the foods reach appropriate internal temperatures
• Clean all cutting boards and utensils immediately after coming into contact with raw meat, poultry, or seafood
• Wash all fruits and vegetables
• Avoid eating raw shellfish if you have any doubt about its origin or freshness
• If traveling overseas, make sure your vaccinations are up to date. If you're planning to visit a developing country, visit the travel health website managed by the Centers for Disease Control and Prevention (CDC) to learn which vaccinations are needed before you go. You can also review any information related to water and local food safety.