Giardia: The Most Common Gut Parasite in the U.S. — Symptoms, Spread and Prevention

Giardia (Giardia duodenalis) is a tiny parasite that causes diarrhea. The illness it causes is called giardiasis. In the United States, more people get sick from Giardia than from any other parasite living in the gut — more than 1 million people every year — and it is found in every region of the country and around the world.

Giardia lives in the intestines of infected people and animals and leaves the body in their stool. Outside the body, in soil for example, it can survive for weeks to months.

Symptoms

Illness usually starts with diarrhea 2 to 5 times a day and growing tiredness. Short-term symptoms include:

• diarrhea
• gas
• smelly, greasy stools that can float
• stomach cramps or pain
• upset stomach or nausea
• dehydration

Symptoms usually appear 1 to 2 weeks after infection and last 2 to 6 weeks. Occasionally they last for years.

Who is at risk

Anyone can get Giardia, but children are more likely to get sick than adults. The risk is higher if you:

• are in close contact with someone who has it, especially in child care
• live somewhere with limited access to safe drinking water
• drink untreated water from springs, lakes, rivers or shallow wells
• swallow water from pools, splash pads, lakes or rivers — while swimming, for example
• have a weakened immune system
• have contact with stool during sex
• have contact with infected animals, or places animals have contaminated with stool

How it spreads

You get sick by swallowing Giardia. Because the germs are in stool, anything stool contaminates can spread them — from person to person, or through water, food, surfaces or objects. It spreads easily: swallowing just a few germs can make you ill.

Prevention

• Wash your hands with soap and water at key times.
• Try not to swallow water when swimming.
• Boil or filter water from lakes, springs or rivers before drinking it or cooking with it. Boiling for at least 1 minute kills Giardia; above 6,500 feet, boil for 3 minutes.
• Wait several weeks after you or your partner no longer have diarrhea before having sex.
• Avoid touching animal stool.
• Clean and disinfect areas where a person or pet recently had diarrhea.

Diagnosis and treatment

If you think Giardia is making you sick, see a health care provider, who will ask for stool samples to test. The provider may prescribe medicine to treat it. If you have diarrhea, drink plenty of water or other fluids to avoid dehydration.

Pets

Animals can pass Giardia to people, but you are unlikely to catch it from a dog or cat: the type of Giardia that sickens people is usually not the type that sickens dogs and cats.

Sources

Based on "About Giardia Infection," Centers for Disease Control and Prevention; a work of the United States government in the public domain.