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Giardiasis is an intestinal illness caused by a microscopic parasite called Giardia lamblia. It is a very commonly reported cause of diarrheal illness in Wisconsin, with an average of 1,200-1,300 cases reported in Wisconsin each year. Cases may occur sporadically or in outbreaks.

Giardia 101

You can get giardiasis if you swallow the Giardia parasite (germ). Giardia—or poop from people or animals infected with Giardia—can contaminate anything it touches. Giardia spreads very easily; even getting tiny amounts of poop in your mouth could make you sick.

Giardiasis can be spread by:

  • Swallowing unsafe food or water contaminated with Giardia germs
  • Having close contact with someone who has giardiasis, particularly in childcare settings
  • Traveling within areas that have poor sanitation
  • Exposure to poop through sexual contact from someone who is sick or recently sick with Giardia
  • Transferring Giardia germs picked up from contaminated surfaces (such as bathroom handles, changing tables, diaper pails, or toys) into your mouth
  • Having contact with infected animals or animal environments contaminated with poop

Giardia infection (giardiasis) can cause a variety of intestinal symptoms, which include:

  • Diarrhea
  • Gas
  • Foul-smelling, greasy poop that can float
  • Stomach cramps or pain
  • Upset stomach or nausea
  • Dehydration

Symptoms of giardiasis generally begin by having two to five loose stools (poop) per day and progressively increasing fatigue. Other, less common symptoms include fever, itchy skin, hives, and swelling of the eyes and joints. Over time, giardiasis can also cause weight loss and keep the body from absorbing nutrients it needs, like fat, lactose, vitamin A, and vitamin B12. Some people with Giardia infections have no symptoms at all.

How long after infection do symptoms appear?

Symptoms of giardiasis normally begin one to two weeks after becoming infected.

How long will symptoms last?

Symptoms generally last anywhere from two to six weeks. In people with weakened immune systems (e.g., due to illness such as HIV), symptoms may last longer. Healthcare providers can prescribe the appropriate antiparasitic medications to help reduce the amount of time symptoms last.

How is giardiasis diagnosed?

Contact your healthcare provider if you think you may have giardiasis. Your healthcare provider will ask you to submit stool (poop) samples to see if you are infected. Because it can be difficult to detect Giardia, you may be asked to submit several stool specimens collected over several days to see if you are infected.

What is the treatment for giardiasis?

Many prescription drugs are available to treat giardiasis. Although Giardia can infect all people, infants and pregnant women may be more likely to experience dehydration from the diarrhea caused by giardiasis. To prevent dehydration, infants and pregnant women should drink a lot of fluids while sick. Dehydration can be life-threatening for infants, so it is especially important that parents talk to their healthcare providers about treatment options for their infants.

Giardia germs spread easily from one person to another; just a small amount of Giardia germs can make someone sick. Because the Giardia germs are in stool (poop), anything that gets contaminated by poop can potentially spread the germs. Understanding how to prevent the spread of Giardia germs can help you protect yourself and your loved ones from getting sick.

Provider Information

Wisconsin case reporting and public health follow-up guidelines: Case Reporting and Investigation Protocol (EpiNet): P-01990 Giardia (PDF)

Guidelines for Prevention and Control - for local public health agencies: Wisconsin Routine Enteric Follow-up Worksheet (PDF)

Questions about Giardia? Contact us!
Phone: 608-267-9003 | Fax: 608-261-4976

Wisconsin Local Health DepartmentsRegional officesTribal agencies

Last revised September 20, 2021