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What is Giardia?

Giardia is a parasite that causes a disease called giardiasis. Giardia is found worldwide, including in the United States.

What are the symptoms of giardiasis?

The most common symptoms are diarrhea, gas or flatulence, stomach cramps, weakness, loss of appetite, and weight loss. Symptoms of giardiasis usually develop 1 to 3 weeks after initial contact. Symptoms can last 2 to 6 weeks. If left untreated, the symptoms can last longer.

Do all people who get infected with Giardia get sick?

No. Some people may not have any symptoms at all.

How is Giardia spread?

Giardia comes out in the stool (poop) of people who are infected. Other people get Giardia by eating the germ. Some ways the infection can spread are:

  • Swallowing Giardia picked up from contaminated surfaces (such as toilets, changing tables, diaper pails, or toys) that contain stool from an infected person or animal
  • Drinking water or using ice made from water sources contaminated with Giardia (such as untreated or improperly treated water from lakes, streams, or wells)
  • Swallowing water while swimming or playing in water contaminated with Giardia, especially in lakes, rivers, springs, ponds, and streams
  • Eating uncooked food that contains Giardia
  • Having contact with the stool of someone who is ill with giardiasis
  • Traveling to countries where giardiasis is common

It is not possible to become infected through contact with blood.

Who can get Giardia?

Anyone can get giardiasis. People more likely to become infected include:

  • Children in child care settings, especially diaper-aged children
  • Close contacts (such as people living in the same household) or people who care for those sick with giardiasis
  • Backpackers, hikers, and campers who drink unsafe water or do not practice good hygiene (such as proper handwashing)
  • People who swallow water while swimming and playing in recreational water where there is Giardia, especially in lakes, rivers, springs, ponds, and streams
  • International travelers
  • People exposed to human feces (poop) through sexual contact
Can pets spread Giardia?

The risk of humans acquiring Giardia infection from dogs or cats is small. The exact type of Giardia that infects humans is usually not the same type that infects dogs and cats.

How is Giardia diagnosed?

If you think you have Giardia, talk to your healthcare provider. Your stool (poop) sample will be tested in the laboratory. The laboratory will look at the sample using a microscope or other test to see if there are any Giardia parasites in it.

How can I prevent Giardia?
  • Always wash your hands for at least 20 seconds with soap and water before preparing or eating food, after using the bathroom, after changing diapers, and after handling your pets.
    • Help young children and other people you are caring for with handwashing as needed.
    • If soap and water are not available, use an alcohol-based hand sanitizer.
  • Do not drink untreated water from a surface water supply, including lakes, rivers, springs, ponds, and streams.
    • If you are not sure the drinking water is safe,, drink bottled water or disinfect tap water by heating it to a rolling boil for 1 minute.
  • Do not swallow water while swimming or playing in water, including lakes, rivers, springs, ponds, and streams.
  • Follow general food safety guidelines, including:
    • Use safe, treated water to wash all food, including fruits and vegetables.
    • Avoid eating raw or uncooked foods when traveling in countries with poor food and water treatment.
    • Learn more at
  • If you are taking care of a person with Giardia, scrub your hands with 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. Always wash your hands after such contact.
 Are there any health regulations for people with Giardia?

Yes. Giardia is a disease that can be spread to other people, so health care providers in Boston are required by law to report cases of Giardia to the Boston Public Health Commission. 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.

Food-related businesses include restaurants, sandwich shops, hospital kitchens, supermarkets, and food processing plants. This regulation also includes workers in schools, residential programs, and child care and health care facilities who feed, give mouth care, or dispense medications to clients.

Boston Public Health Commission
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