Viruses, Bacteria and Parasites in the Digestive Tract

Viruses, bacteria and parasites are living organisms that are found all around us. They exist in the water and soil, on the surfaces of foods that we eat and on surfaces that we touch. Some bacteria live in and on our bodies and do not cause problems. Other kinds of bacteria (as well as parasites and viruses) can make us quite ill if they invade our bodies. Bacteria and viruses can live outside of the human body (for instance, on a countertop) sometimes for many hours or days. Parasites, however, require a living host in order to survive.

Bacteria and parasites can usually be destroyed with antibiotics. On the other hand, antibiotics cannot kill viruses. Children with viral illnesses can be given medications to improve their course or outcome, but antibiotics are ineffective against treating these infections.

Bacteria, viruses and parasites can cause a wide variety of illnesses, and can infect any of the organs of the body. Viruses are often responsible for respiratory illnesses (such as the common cold) and digestive illnesses (such as vomiting and diarrhea). Bacteria can infect any part of the body, but often cause diarrhea when they invade the digestive tract. A child is considered to have diarrhea when their bowel movements are both more frequent and looser than usual. Learn more about diarrhea.

Frequently Asked Questions about Viruses, Bacteria and Parasites in the Digestive Tract

How does a child usually come in contact with bacteria, viruses or parasites that cause diarrhea?

  • When touching the stool of an infected person (such as when touching soiled diapers)
  • When touching an object contaminated with the stool of an infected person, and then ingesting the germs–this usually occurs by touching the mouth with a contaminated hand (can occur at day care centers or at home in areas where diapered babies play)
  • By ingesting contaminated food or water.

Why is infection with these organisms a concern?

Viruses, bacteria and parasites that invade the digestive tract usually cause diarrhea. Large amounts of water can be lost with the diarrhea. Children become dehydrated much quicker than adults, and this can lead to serious problems if fluids are not replaced. Infections caused by parasites and bacteria may need treatment with medications.

Children with a severely weakened immune system are at an increased risk for more serious side effects from the diarrhea. These children include those with HIV/AIDS, cancer or inherited diseases that affect the immune system. Transplant patients who are taking certain immunosuppressive drugs are also at increased risk for more severe symptoms that could lead to serious illness.

Can my child get germs from food?

Almost everyone has experienced a foodborne illness at some point in time. Contrary to popular belief, foodborne illnesses can occur when food is prepared at a restaurant or at home. If food is handled and prepared safely, most foodborne illnesses can be avoided.

All food may contain some natural bacteria, and improper storage or handling gives the bacteria a chance to grow. Also, food can be contaminated with bacteria from other sources that can make people sick. Contaminated or unclean food can be very dangerous, especially to children. According to the CDC, each year foodborne illnesses kill 3,000 people of all ages. They also cause fever, stomach cramps, vomiting and diarrhea in an estimated 48 million Americans.

Four major tips recommended by the CDC to prevent contaminating food

  • Use caution when buying food:
    – When at the grocery store, pick up perishable food such as meat, eggs and milk at the very end of your shopping, so they will stay cool.
    – Take food home right away so that it does not spoil in a hot car.
    – Avoid raw or unpasteurized milk.
    – Because eggs, meat, seafood and poultry are most likely to contain bacteria, do not allow their juices to drip on other food.
  • Store food properly:
    – Store eggs, raw meat, poultry and seafood in the refrigerator.
    – A refrigerator should be set between 32 degrees F and 40 degrees F.
    – A freezer should be set at or below 0 degrees F.
    – Regularly clean and disinfect the refrigerator and freezer.
    – Use containers to prevent contaminating other foods or kitchen surfaces. Do not store food uncovered in the refrigerator or freezer.
  • Use special precautions when preparing and cooking food:
    – Wash your hands and clean and disinfect kitchen surfaces before, during and after handling, cooking and serving food.
    – Defrost frozen food on a plate either in the refrigerator or in a microwave, but not on the counter.
    – Cook food immediately after defrosting.
    – Use different dishes and utensils for raw foods than you use for cooked foods.
    – Wash raw fruits and vegetables before eating them.
  • Cool and promptly store leftovers after food has been served:
    – Because harmful bacteria grow at room temperature, keep hot food hot and keep cold food cold. This is especially important during picnics and buffets.
    – Do not leave perishable foods out for more than two hours.
    – Promptly refrigerate or freeze leftovers in shallow containers or wrapped tightly in bags.

Wash Up For Good Health

Practicing proper handwashing inside and outside the home goes a long way in minimizing the risks of illness from viruses, bacteria and parasites.

What To Do When Diarrhea Strikes

Every child end ups up with diarrhea every once in a while no matter how hard families try to protect their children from illness. Learn what to do if your child has diarrhea and when to call the doctor.

Common Bacteria, Viruses and Parasites That Cause Diarrhea

Escherichia coli O157:H7 is just one of the hundreds of strains of the bacterium Escherichia coli (E. coli). Most strains of E. coli are harmless and live in the intestines of healthy humans and animals. E. coli, however, produces a powerful toxin that can cause a severe infection. (The combination of letters and numbers in the name of the bacterium refers to the specific markers found on its surface and distinguishes it from other types of E. coli.)

The CDC recognizes E. coli as a foodborne illness, which means the bacteria spreads because it is on a piece of food, eaten by a person or people and then the person gets sick. Infection often leads to bloody diarrhea, stomach cramps, vomiting and fever.

How does E. coli spread?

Most E. coli illness has been associated with eating undercooked, contaminated ground beef. E. coli bacteria live in the intestines of healthy cattle and, although the number of organisms required to cause disease is not known, it is suspected to be very small. Meat becomes contaminated during slaughter, and organisms can be thoroughly mixed into beef when it is ground. Contaminated beef looks and smells normal. Other ways to transmit E. coli include:

  • Person-to-person contact in families and in child-care and other institutional-care centers can also be places where the transmission of the bacteria can occur.
  • Bacteria present on a cow's udders, or on equipment, may get into raw milk causing the infection.
  • Infection may also occur after swimming in or drinking sewage-contaminated water.
  • It has been confirmed that unpasteurized juices, such as apple cider, may also cause the infection.
  • Bacteria in diarrhea stools of infected people can be passed from one person to another if hygiene or handwashing habits are inadequate. This is particularly likely among toddlers who are not toilet trained. Family members and playmates of these children are at high risk of becoming infected.

Young children typically shed the organism in their feces for a week or two after their illness resolves.

How to prevent getting sick from E. coli:

The CDC recommendations for preventing of E. coli infection include:

  • Cook all ground beef or hamburger thoroughly. Make sure that the cooked meat is gray or brown throughout (not pink), any juices run clear, and the inside is hot.
  • Using a digital instant-read meat thermometer, the temperature of the meat should reach a minimum of 160 degrees F.
  • If you are served an undercooked hamburger in a restaurant, send it back.
  • Consume only pasteurized milk and milk products. Avoid raw milk.
  • Consume only pasteurized juices and ciders.
  • Make sure that infected people, especially children, wash their hands carefully and frequently with soap to reduce the risk of spreading the infection.
  • Drink municipal water that has been treated with adequate levels of chlorine, or other effective disinfectants.
  • Avoid swallowing lake or pool water while swimming.
  • Wash hands thoroughly after using the toilet.
  • People with diarrhea should not: - Swim in public pools or lakes - Bathe with others - Prepare food for others.

Salmonella is a bacterium that infects the intestines and causes diarrhea, fever, and abdominal cramps 12 to 72 hours after infection. Over 1 million cases of salmonella infection are reported in the United States each year. The illness usually lasts four to seven days and most people recover without treatment.

However, in some people the diarrhea may be so severe that the patient needs to be hospitalized. In those patients, the Salmonella infection may spread from the intestines to the blood stream and then to other body sites, and can cause death unless the person is treated promptly with antibiotics. Infants and those with impaired immune systems are more likely to have a severe illness.

How does Salmonella spread?

Salmonella may be spread by:

  • Eating raw foods contaminated with animal feces. Contaminated foods usually look and smell normal. Contaminated foods are often of animal origin, such as beef, poultry, milk or eggs. However, all foods may become contaminated, including some unwashed fruits and vegetables and peanut butter. Many raw foods of animal origin are frequently contaminated, but thorough cooking kills Salmonella.
  • Handling reptiles. Reptiles (such as iguanas and turtles) are particularly likely to harbor Salmonella and people should always wash their hands immediately after handling a reptile, even if the reptile is healthy. Adults should also be careful that children wash their hands after handling a reptile.

How to prevent getting sick from Salmonella:

Since foods of animal origin pose the greatest threat of Salmonella contamination, do not eat raw or undercooked eggs, poultry or meats. Remember that some sauces and desserts use raw eggs in their preparation, so be cautious of these, particularly in foreign countries. Also, follow these recommendations by the CDC:

  • Make sure poultry and meat, including hamburgers, are well cooked, not pink in the middle.
  • Do not consume raw or unpasteurized milk or other dairy products.
  • Thoroughly wash produce before eating it.
  • Avoid cross-contamination of foods. Uncooked meats should be kept separate from produce, cooked foods, and ready-to-eat foods.
  • All utensils, including cutting boards, knives, etc. and counters should be thoroughly washed after handling uncooked foods.
  • Thoroughly wash hands before handling foods and between handling different food items.
  • Thoroughly wash hands after contact with feces.
  • Thoroughly wash hands after handling any reptiles, since reptiles are particularly likely to have Salmonella.

Rotavirus is a very common cause of diarrhea among children.

In the United States, the disease occurs most often in the winter, with annual epidemics occurring from December to June. The highest rates of illness occur among infants and young children, and most children in the United States are infected by 5 years of age. Adults can also be infected, but their illnesses tend to be mild.

The incubation period for rotavirus disease is approximately two days. The disease is characterized by vomiting and watery diarrhea for three to eight days, and fever and abdominal pain occur frequently. Immunity after infection is incomplete, but repeat infections tend to be less severe than the original infection.

How is rotavirus spread?

Rotavirus may be spread:

  • Through accidentally swallowing the virus picked up from surfaces contaminated with stool from an infected person, such as toys, bathroom fixtures, changing tables and diaper pails.
  • Through ingestion of contaminated food, or contaminated water, such as the type of water found in a public swimming pool.

How to prevent rotavirus infection:

Infants can receive a vaccination for rotavirus. Additionally, handwashing is a very important means of preventing the spread of rotavirus. Careful and frequent handwashing can prevent the spread of infection to other people.

The CDC recommends:

  • Adults should wash their hands after using the toilet, after helping a child use the toilet, after diapering a child and before preparing, serving or eating food.
  • Children should wash their hands after using the toilet, after having their diapers changed (an adult should wash infant's or small child's hands) and before eating snacks or meals.
  • Frequently disinfect toys, bathrooms and food preparation surfaces, especially if a sick child has been in the home.
  • Use diapers with waterproof outer covers that can contain liquid stool or urine, or use plastic pants.
  • Make sure that children wear clothes over diapers.

During the past 15 years, Giardia lamblia has become recognized as one of the most common waterborne diseases in the United States. Giardia is a tiny parasite that lives in the intestines of people and animals. The parasite is passed in the bowel movement of an infected person or animal. It is found in every region of the United States and throughout the world. Diaper-aged children who attend day care centers, international travelers, hikers, campers and others who drink untreated water from contaminated sources are most at risk for developing infection with Giardia. Several community-wide outbreaks of infection have been linked to drinking municipal water contaminated with Giardia.

How does Giardia spread?

People become infected after accidentally swallowing the parasite. Giardia may be found in soil, food, water or on surfaces.

Some of the ways people can become infected with Giardia include:

  • Eating uncooked food contaminated with Giardia.
  • Swallowing water from swimming pools, lakes, rivers, springs, ponds or streams contaminated with sewage or feces from humans or animals.
  • Accidentally swallowing the parasite picked up from surfaces contaminated with stool from an infected person, such as toys, bathroom fixtures, changing tables and diaper pails.

How to prevent ingesting Giardia:

The CDC recommends:

  • Washing hands with soap and water after using the toilet, changing diapers and before handling food.
  • Washing and peeling all raw vegetables and fruits before eating. • Avoiding drinking water from lakes, rivers, springs, ponds or streams unless it has been filtered and chemically treated.
  • Boiling drinking water for one minute to kill the Giardia parasite. This will ensure safe drinking water during community-wide outbreaks caused by contaminated drinking water.
  • When camping or traveling in countries where the water supply may be unsafe, avoid drinking unboiled tap water and avoid uncooked foods washed with unboiled tap water. Bottled or canned carbonated beverages, seltzers, pasteurized fruit drinks and steaming hot coffee and tea are safe to drink.
  • If your child has Giardia, avoid swimming in pools for two weeks after the diarrhea or loose stools have cleared. Giardia is fairly chlorine resistant and is passed in the stools of infected people for several weeks after they no longer have symptoms.

Cryptosporidium, often referred to as "crypto," is a tiny parasite that can live in the intestines of humans and animals. The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very resistant to chlorine disinfection.

How does cryptosporidium spread?

Cryptosporidium may be spread by:

  • Accidentally swallowing anything that has come in contact with the stool of a person or animal.
  • Swallowing contaminated water from swimming pools, hot tubs, lakes, rivers, springs, ponds or streams contaminated with sewage or feces from humans or animals.
  • Eating uncooked contaminated food.
  • Picking cryptosporidium up from surfaces contaminated with stool from an infected person (such as toys, bathroom fixtures, changing tables and diaper pails).

How to prevent getting ill from cryptosporidium:

The CDC recommends:

  • Your child should wash their hands with soap and water after using the toilet, changing diapers and before eating or helping prepare food.
  • Avoid water or food that may be contaminated.
  • Washing and/or peeling all raw vegetables and fruits before giving them to your child to eat.
  • Avoiding drinking water from lakes, rivers, springs, ponds or streams unless it has been filtered and chemically treated.
  • Boiling drinking water for one minute to kill the cryptosporidium parasite. This will ensure safe drinking water during community-wide outbreaks caused by contaminated drinking water.
  • When camping or traveling in countries where the water supply may be unsafe, avoid drinking unboiled tap water and avoid uncooked foods washed with unboiled tap water.
  • Avoiding swimming in pools if your child has had cryptosporidium and for at least two weeks after diarrhea stops. Crypto can be passed in the stool and contaminate water for several weeks after your child no longer has symptoms. This has resulted in several outbreaks of cryptosporidium among pool users. Crypto can survive in chlorinated pools for several days.