When you were a kid, did you like to chant "diarrhea, diarrhea" to make your friends laugh? Now you probably associate the word with discomfort and embarrassment because having diarrhea is no fun. But nearly everybody gets it once in a while, and it's usually caused by gastrointestinal infections.

What Are Gastrointestinal Infections?

Diarrhea, which is characterized by frequent and watery bowel movements, is often caused by gastrointestinal infections, although it can also come from other illnesses or changes in diet. Germs such as parasites, viruses, or bacteria all can cause gastrointestinal (GI) infections.

Which germs are responsible for diarrhea depends on the geographic area a person lives in and its level of sanitation, economic development, and hygiene standards. For example, countries that have poor sanitation or use human waste as fertilizer tend to have outbreaks of diarrhea when intestinal bacteria or parasites contaminate crops or drinking water.

In developed countries like the United States, outbreaks of diarrhea are most often caused by what we call food poisoning. Food poisoning happens when toxins made by bacteria in food that is not handled, stored, or cooked properly make a person sick.

The viruses that cause diarrheal illness, also known as viral gastroenteritis, can pass through a household (or a college dorm or other place where lots of people live together) quickly because they're highly infectious. Luckily, the diarrhea usually goes away on its own in a few days. For healthy teens and adults, viral gastroenteritis is a common but minor inconvenience. But for small children and people with chronic illnesses, it can lead to dehydration that requires medical attention.

Many different types of bacteria and parasites can also cause GI infections and diarrhea. Most are not serious and go away after a few days, but others can be quite serious.

Common GI Infections

Here are a few types of GI infections that you may have heard about:

• Salmonella bacteria lead to between 1 and 5 million cases of diarrheal illness in the United States each year. These bacteria are a major cause of food poisoning and are frequently found in raw chicken or eggs.
• Shigella bacteria are highly contagious and spread easily from person to person. They attack the intestinal wall and may cause ulcers that bleed. Shigella infections account for more than 160 million cases of diarrhea around the world each year.
• E. coli bacteria are found in the bowel movements of people and animals. Some strains of the bacteria secrete a toxin that can be life threatening for small children and older people. Others can cause traveler's diarrhea, a milder infection. E. coli infections spread through direct person-to-person contact or contaminated water or food, such as undercooked beef in hamburgers or unwashed fruit that came into contact with animal manure.
• The Giardia parasite, which spreads easily through contaminated water and human contact, is another common cause of diarrheal infections in the United States. This parasite can spread in water parks and pools because it is resistant to chlorine treatment. Bathing in and drinking water from contaminated streams or lakes can also lead to an infection and chronic diarrhea. Infants in child-care settings often become infected with Giardia and can bring the parasite home, causing diarrhea in family members.
• Another parasite, Cryptosporidium, is a common culprit behind diarrhea epidemics in childcare centers and other public places. Cryptosporidium often causes watery diarrhea that can last for 2 weeks or more.

What Are the Signs and Symptoms?

Usually GI infections cause abdominal cramping followed by diarrhea. You may also experience:

• fever
• loss of appetite
• nausea
• vomiting
• weight loss
• dehydration
• mucus or blood in the stool

These symptoms typically last for a few days or longer. If your symptoms last for more than 2 weeks, however, you have chronic diarrhea. Call your doctor if you think that you have chronic diarrhea or if you see blood in your stool.

When Will Symptoms Appear?

The incubation period for a gastrointestinal infection can vary depending on the particular germ causing it. For example, the Shigella incubation period is usually 2 to 4 days, but the period for viral infections ranges from 4 to 48 hours.

Parasitic infections generally have longer incubation periods, such as a Giardia infection, in which symptoms can take from 1 to 4 weeks to appear. Then, depending on the type of germ and the person's overall health, a diarrheal infection can last for a few days or a few weeks.

How Long Are GI Infections Contagious?

Diarrheal infections are highly contagious. They can spread from person to person via dirty hands, contaminated food or water, and some pets. Most cases are contagious for as long as a person has diarrhea, but some infections can be contagious for even longer.

Can I Prevent These Infections?

The most effective way to prevent contagious diarrheal infections is to wash your hands frequently. Dirty hands carry germs into the body when you do things like bite your nails or use your hands when eating.

It's important to always wash your hands with soap and water thoroughly after using the bathroom and before eating, especially if you know there's an illness going around. Making sure your bathroom surfaces are clean can also help to prevent infections.

Food and water can also spread germs that cause diarrhea. To help protect yourself, cook foods thoroughly and wash raw fruits and vegetables well before eating them. Avoid eating pink hamburgers or other undercooked meat, and always refrigerate leftovers quickly — your delicious turkey dinner can grow nasty bacteria after just a few hours of sitting on the counter.

Make sure your kitchen counters and cooking utensils are clean, too, especially after they've been in contact with raw meat, eggs, and poultry. Avoid eating food that's been left out for a few hours, even if it's been reheated, because toxins can still survive in the food.

If you're traveling or camping, never drink from streams, springs, or lakes unless local health authorities have certified the water safe for drinking. In some developing countries, you may want to stick to bottled water and drinks rather than tap water — and be careful about buying food from street vendors.

Pets, particularly reptiles, can also spread germs if they aren't kept away from family eating areas. Never wash pet cages or bowls in the same sink that your family uses to prepare meals. And always wash your hands after handling your pet!

Should I Call My Doctor?

Sometimes, despite your best efforts, you can't prevent diarrheal infections. Tell an adult if you have diarrhea, fever, vomiting, or severe abdominal pain. That person can help you decide whether to call your doctor.

If you feel listless and your mouth and skin feel dry, or if your bowel movements contain blood or mucus, you should contact or see a doctor right away. You should also go to the doctor if you are vomiting so much that you can't keep down fluids or if your symptoms last more than 3 days.

How Are These Infections Treated?

Most infections that cause diarrhea, especially viral infections, will go away without treatment. Taking it easy at home and drinking plenty of fluids to avoid dehydration are the best ways to ride out the illness. If you do become dehydrated, you might need to go to the hospital for intravenous (IV) fluids to replace those lost to diarrhea, vomiting, and fever.

If you end up visiting your doctor, you may need to give a stool sample so he or she can find out what type of infection you have. Whether you need medicine will depend on which germ is causing the illness. If you have a parasitic infection, it will probably be treated with antiparasitic medicine to cure the illness.

Most GI infections caused by viruses and many bacterial infections do not need treatment, but someone with a weakened immune system who gets a bacterial intestinal illness may need to take prescription antibiotics to prevent the infection from spreading throughout the body.

What Can I Do to Feel Better?

You'll feel better if you stay well hydrated, so drink lots of water. In addition to fluid that is lost during bouts of diarrhea, electrolytes (sodium and potassium) are also lost and need to be replaced because the body cannot function properly without them. Try sipping broth or soup, which contain sodium, and 100% fruit juice (with no added sugar), which contains potassium.

When you feel ready to eat something more substantial, try soft fruits or vegetables, which also contain potassium. Avoid milk products and fatty, high-fiber, or very sweet foods until the diarrhea subsides, and don't drink sports drinks or soft drinks — although they contain electrolytes, their high sugar content may aggravate diarrhea.

As uncomfortable as diarrhea may be, it is usually short-lived. Drink enough fluids and follow your doctor's instructions, and usually you'll be feeling better in no time.

Reviewed by: J. Fernando del Rosario, MD
Date reviewed: March 2012