Updated: May 21, 2026
What is Giardiasis?
Giardiasis (GEE-are-DYE-uh-sis) is a diarrheal illness caused by the flagellated, protozoan parasite Giardia duodenalis (also known as G. lamblia or G. intestinalis). Giardia is a common cause of waterborne disease (drinking and recreational) in humans and can be found in every region of the United States and throughout the world. In 2022, the Centers for Disease Control and Prevention (CDC) reported 13,819 cases of giardiasis in the United States. Annually, South Carolina reports an average of 128 cases.
What are the symptoms?
Symptoms include diarrhea, stomach cramps, and upset stomach. These symptoms may lead to weight loss and dehydration. Symptoms generally begin 1-2 weeks after being infected. In otherwise healthy persons, symptoms generally last up to 2-6 weeks; however, symptoms may last longer. Some people have no symptoms.
How is Giardiasis treated?
Several prescription drugs are available to treat Giardia, so be sure to contact your health care provider. Although Giardia can infect all people, young children and pregnant women may be more susceptible to dehydration resulting from diarrhea. Thus, it is advised that these people should drink plenty of fluids while ill.
How do people catch this disease?
Giardia lives in the intestines of infected humans or animals. You can become infected after accidentally swallowing the parasite. Giardia may be found in soil, food, water, or surfaces that have been contaminated with the feces from infected humans or animals. Giardia spreads quickly and ingesting even a small number of Giardia germs can make you ill. Giardiasis can be spread by:
- Putting something in your mouth, or accidentally swallowing something, that has come in contact with the stool of a person or animal infected with Giardia
- Swallowing recreational water contaminated with Giardia. Recreational water is water in swimming pools, hot tubs, jacuzzis, fountains, lakes, rivers, springs, ponds, or streams that can be contaminated with sewage or feces from humans or animals
- Eating uncooked or undercooked food contaminated with Giardia
- Accidentally swallowing the parasite picked up from surfaces (such as toys, bathroom fixtures, changing tables, diaper pails) contaminated with stool from an infected person
*Note: Giardiasis is not spread by contact with blood. Additionally, while animals can transmit Giardia to humans, it's unlikely you'll contract a Giardia infection from dogs or cats. The strain of Giardia that affects people is typically different from the one that causes illness in dogs and cats.
What can be done to stop the spread of this disease?
- Washing your hands with soap and water after using the toilet, changing diapers, and before eating or preparing food is the best way to stop the spread of Giardia.
- Avoid water that might be contaminated. Avoid swallowing recreational water. Avoid drinking untreated water from shallow wells, lakes, rivers, springs, ponds, and streams. Avoid using ice or drinking untreated water when traveling in countries where the water supply might be unsafe.
- Avoid swimming in recreational water (pools, hot tubs, lakes or rivers, the ocean, etc.) if you have Giardia, and for at least 2 weeks after diarrhea stops. You can pass Giardia in your stool and contaminate water for several weeks after your symptoms have ended.
- Wash and/or peel all raw vegetables and fruits before eating.
- Wash all food that is to be eaten raw. Avoid eating uncooked foods when traveling in countries with minimal water treatment and sanitation systems.