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What is Giardia?
Giardia lamblia is a common waterborne parasite that causes the diarrheal illness giardiasis.

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How is it Spread?

Giardia lamblia is a waterborne parasite that lives in the intestine of infected humans or animals. You can become infected after accidentally swallowing the parasite or via contact with blood.

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Over 15,000 Documented Cases Each Year in the U.S.

SYMPTOMS: Symptoms of giardiasis may last anywhere between two and six weeks and include diarrhea, stomach cramps, nausea, and other intestinal symptoms.

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Giardia Levels Range From 10,000 to 100,000 CYSTS/L in Untreated Sewage, 10 to 100 CYSTS in Treated Sewage, And 10 Or Fewer CYSTS/L in Tap Water

Giardia is passed in the stool of an infected person, and may also be present in soil, food, and water. It is commonly transmitted in swimming pools or from swallowing water that has come in contact with the feces of a person or animal infected with Giardia.

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Giardia have been proven to be extremely resistant to oxidant treatments such as chlorine.

States with Incidence Higher than 10 Cases per 100,000 Population of Giardiasis

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This map represents the rate of instance annually as reported to the National Notifiable Diseases Surveillance System.


The EPA recommends filtration and UV disinfection for controlling and preventing Giardia in water systems.

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