Fact sheet about Giardia

What is Giardia?

Giardia is germ (a parasite) that causes an infectious disease (called “giardiasis”) that affects the stomach and bowels. Giardia germ is a common cause of diarrhea in the United States.

What are the symptoms of giardiasis?

The most common symptoms are diarrhea, foul-smelling soft stools, abdominal cramps, bloating, increased gas, weakness, loss of appetite and weight loss. Symptoms of giardiasis usually appear seven to ten days (but sometimes as long as four weeks) after the germs are swallowed. The symptoms may come and go for weeks in a person who is not treated.

Do all people who are infected with Giardia get sick?

No. Some people who are infected with the parasite may only have minor symptoms and some people may not have any symptoms at all.

How is giardiasis spread?

The parasites must be swallowed to cause disease. You can get a Giardia infection if you swallow food or water which has been contaminated with the parasite. Once swallowed, the parasites multiply in the small intestine and are passed out with bowel movements. Giardiasis is often spread when people do not wash their hands with soap and water after using the toilet or changing a diaper. People who get the germs on their hands can infect themselves by eating, smoking, or touching their mouths. They can also spread the germs to things they touch, including food, which can then make others sick. The giardia parasites are mainly spread from person to person, such as in daycare centers and institutions where personal hygiene may be poor due to age (infancy, elderly) or disability. Giardiasis can also be spread this way in a household setting.

Can giardiasis be spread by animals?

Yes. Giardia parasites have been found in the stools of many animals, including rodents, dogs, cats, cattle, and wild animals. Animals living near water supplies, such as beavers and muskrats, have been found to be infected with Giardia. When those animals contaminate the water with their stool, people can get sick if they drink the water.

How can you know for sure if you have giardiasis?

Your doctor, nurse, or health center must send your stool sample to a laboratory. The laboratory will look at the sample with a microscope to see if there are any Giardia parasites in it. The germs are often hard to see, so they may need several stool samples from you. This is the most common way of finding out if someone has giardiasis. Giardia can also be diagnosed by a laboratory test of a sample of fluid or a biopsy from the small intestine.

What is the treatment for giardiasis?

There are several medicines that are used to treat Giardia infection. They are only available by prescription from your physician. Other treatment for diarrhea, such as drinking more fluids, may also be recommended by your physician.

How can giardiasis be prevented?

Giardiasis can be prevented by practicing good hygiene and by using caution before drinking water from an unknown source.

Some general guidelines are:

  • Always wash your hands thoroughly with soap and water before meals, before preparing food, after using the toilet, after changing diapers, and after handling your pets.
  • Do not drink untreated water from a surface water supply, such as a pond, lake, or stream. Although the water may appear to be clean, it may contain Giardia parasites, which cannot be seen without a microscope. If untreated water is all that is available, boil the water for one minute before drinking it.
  • If you are taking care of a person with giardiasis, scrub your hands with plenty of soap and water after contact with the person’s stool (for example, after changing diapers). Promptly and carefully dispose of any material that has been contaminated with stool, and always wash your hands after such contact.
  • If your source of drinking water is a well or a private surface water supply, do not allow humans or animals to defecate (have bowel movements) near the water. Contact your local health department for advice on how keep your water supply safe. Also, some water filters can help to get rid of parasites from contaminated water.

Are there any health regulations for people with giardiasis?

Yes. Because giardiasis is a disease that can easily spread to other people, health care providers are required by law to report cases to the local board of health.

In order to protect the public, workers at food-related businesses who have giardiasis must stay out of work until they don’t have diarrhea and a lab test on a stool sample shows that there are no Giardia parasites. Workers in food-related businesses who have diarrhea and live with someone who has giardiasis must also show that they have no Giardia parasites in their stool. Food-related businesses include restaurants, sandwich shops, hospital kitchens, supermarkets, dairy or food processing plants. This regulation also includes workers in schools, residential programs, day-care and health care facilities, who feed, give mouth care or dispense medications to clients.

Where can you get more information?

  • Your doctor, nurse or clinic
  • The Centers for Disease Control and Prevention (CDC) website
  • Your local board of health (listed in the telephone directory under “government”)
  • The Massachusetts Department of Public Health (MDPH), Division of Epidemiology and Immunization at (617) 983-6800.

Spanish and Portuguese translations of this fact sheet are available under additional resources.

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