Giardia Infection: Frequently Asked Questions

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Many people ask if Giardia is bacteria, but in fact it is a parasite. Giardia infection (giardiasis) is caused by the parasite Giardia lamblia, which can be found everywhere in the world. It lives in soil, water, food and feces. You can become infected by ingesting the parasite. Here’s what you need to know about this increasingly common parasitic infection.

How do you get a Giardia infection?

In the United States, people most commonly ingest the Giardia parasite by:

  • Eating food contaminated by the parasite
  • Transferring the parasite from a contaminated surface or substance to their hands and then to their mouths
  • Swallowing (or consuming ice made from) untreated water from rivers, lakes or wells
  • Accidental ingestion of contaminated water in swimming pools, spas/hot tubs, and interactive water features

Because Giardia lives everywhere in the world, your risk of becoming ill from giardiasis increases if you drink from local sources when traveling to places with untreated water or poor sanitation.

Is Giardia contagious?

Giardia infection is not directly contagious, but the Giardia parasite is highly transmissible. When it is not inhabiting a host, this parasite encases itself in a hard shell called a cyst. These cysts survive easily in human feces, which is the primary way this parasite is transmitted between people. In fact, Giardia transmission is common in childcare settings due to fecal transfer during diaper changes. If a person picks up Giardia on their fingers when changing a diaper and does not thoroughly wash their hands afterwards, they can deposit the parasite’s cysts on everything else they touch—where the next person to touch the item can pick up the cysts and ingest them.

The best way to prevent transmitting Giardia (and many other infectious agents) is by washing your hands frequently—and especially after performing a diaper change, having a bowel movement, or performing other personal hygiene tasks for yourself or someone else.

What are the symptoms of giardiasis?

Not everyone with a Giardia infection develops symptoms. When people do get sick from this parasite, the symptoms typically develop within two weeks of ingesting the parasite and include:

  • Diarrhea that is watery and sometimes smells bad
  • Gas and bloating
  • Greasy stools, especially ones that alternate with diarrhea
  • Weight loss

Severe symptoms can also cause dehydration. If an infant, pregnant woman, or elderly person exhibits signs or symptoms of giardiasis, they should seek medical attention and drink plenty of water.

Does Giardia go away on its own?

In many cases, Giardia infection goes away on its own. Symptoms of giardiasis usually last from 2 to 6 weeks. However, some people develop an ongoing infection without treatment. You can become infected with Giardia more than once, although symptoms may not be as severe with future infections.

People with poorly functioning immune systems may not clear the infection as quickly as people with health immune systems.

How is Giardia infection treated?

Anyone with suspected giardiasis should seek medical care. Giardia treatment in humans involves a prescription medicine that destroys the parasite and clears your symptoms faster. Treatment may be necessary for complications of giardiasis too, such as dehydration or nutritional deficiency.

If a person does not develop symptoms of giardiasis, no treatment is necessary.

Can Giardia be prevented?

Giardiasis cannot be entirely prevented, because the parasite is so widespread. However, you can reduce your risk of ingesting the parasite by:

  • Drinking bottled water when traveling
  • Practicing good hand hygiene at all times
  • Purifying fresh water from lakes, rivers and streams when camping or engaging in backcountry activities
  • Washing fresh fruits and vegetables
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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Dec 14
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. Giardia Infections. MedlinePlus, U.S. National Library of Medicine.
  2. Giardia Infection. MedlinePlus, U.S. National Library of Medicine.
  3. Parasites – Giardia. General Information. U.S. Centers for Disease Control and Prevention.
  4. Giardia Infection (Giardiasis). Mayo Clinic.