What is Giardiasis?

A tiny parasite called Giardia intestinalis causes this diarrheal disease. This bug lives all around the world in places that don’t have clean drinking water. It’s a common cause of waterborne illness in the U.S.

How Do You Get It?

Usually from the stool of an infected person or animal. Before they’re pooped out, the parasites grow a hard shell called a cyst. It helps them live for months outside the body, either in water or on a surface. The infection comes after you encounter the parasite or a cyst. You might:

  • Touch contaminated surfaces like bathroom handles, changing tables, diaper pails, or toys, then eat without washing your hands
  • Drink water or use ice made from an untreated water source -- like a lake, stream, or well -- that’s home to giardia
  • Swallow the parasite while you swim or play in water
  • Eat uncooked food that contains giardia
  • Come into close contact with someone who has giardiasis
  • Travel to countries where it’s common

Who’s at Risk?

While anyone can catch giardiasis, some people are more likely than others to get the infection:

  • Parents and child care workers who change diapers
  • Children in child care centers
  • People who live in the same household as someone with giardiasis
  • Those who drink water or use ice made from untreated water
  • Backpackers, hikers, and campers who drink unsafe water or who don’t practice good hygiene (like proper handwashing) on the trail
  • International travelers
  • People who have anal sex

How Do You Prevent It?

There isn’t a vaccine, but there are steps you can take:

  • Wash your hands after you use the toilet, after you change diapers, and before you eat or prepare food.
  • Filter or boil water if you’re outdoors.
  • Try not to swallow water when you swim in a pool, lake, or stream.
  • Drink bottled water when you travel to places with unsafe water.
  • Use a condom if you have anal sex.

What Are the Symptoms?

They usually start 1 to 3 weeks after you’re exposed. They’ll probably last for 2 to 6 weeks. The most common include:


When Should I Call a Doctor?

Let your doctor know if:

  • Your symptoms -- including loose stools and nausea -- last more than a week
  • You show signs of dehydration, such as extreme thirst, dizziness, or confusion

Tell her about any recent travels, interactions with children in diapers, or swimming or drinking from a body of water. She’ll collect a series of stool samples over several days to make a diagnosis.

How Is It Treated?

Many people get better without treatment. But if your symptoms last more than several weeks, or you’re likely to spread the parasite, your doctor can give you medication. Metronidazole (Flagyl), nitazoxanide (Alinia), and tinidazole (Tindamax) are among the drugs used to treat giardia infections.

WebMD Medical Reference Reviewed by Laura J. Martin, MD on February 15, 2018



Medscape: “Giardiasis: Background.”

CDC: “Parasites -- Giardia: General Information,” “Parasites -- Giardia: Treatment.”

Mayo Clinic: Dehydration: Overview: Symptoms & causes,” “Giardia infection (giardiasis): Overview: Symptoms & causes,” “Giardia infection (giardiasis): Overview: Diagnosis & treatment.”

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