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Infectious Diseases


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What is Giardiasis?

Giardiasis is an infection caused by the parasite Giardia.  When this parasite is ingested it can cause a diarrheal illness. Giardia can be found in soil, food, water and on surfaces or hands that have been contaminated with the stool of an infected person or animal.

How is it spread?

Giardiasis is spread by swallowing the parasite through something that has been contaminated with the stool of an infected person or animal. Common examples are drinking water, recreational water, and contaminated food.

Coming into contact with the stool of an infected person, child or infant (for example, during diaper changes) may be another source of exposure.

Pets and wild animals can be infected with Giardia. Not properly washing your hands after handling or cleaning up after these animals can expose you to the parasite.

What symptoms should I watch for?

Some people can be infected and not have any symptoms.  Common symptoms may frequent diarrhea, pale and greasy stools, abdominal cramps and bloating. These symptoms may lead to weight loss and dehydration. Symptoms can begin 3-25 days (average is 7-10 days) after you are exposed to the parasite. Most healthy persons recover in 2 to 4 weeks.

What is the treatment for Giardiasis?

Your health care provider may suggest antibiotics. It is important to drink plenty of fluids when you have diarrhea so you do not become dehydrated.

How do I protect myself and others?

  • Always wash your hands after using the toilet, before preparing or eating meals, after changing diapers, after engaging in sexual activity, and after being in close contact with pets and wild animals.
  • Do not drink untreated water from shallow wells, lakes, rivers, springs, ponds and streams. The amount of chlorine used in routine water treatment does not kill Giardia, especially when the water is cold. If you are unsure of the safety of your drinking water, boil your water for 1 minute to destroy the parasite or use an approved filtration system that will remove it.
  • Avoid swallowing potentially contaminated recreational water (e.g. swimming pools, wading pools, lakes, rivers, streams).
  • Do not drink raw or unpasteurized milk and fruit juices.
  • Wash and/or peel all raw vegetables and fruits before eating. Use safe, uncontaminated water to wash all foods that are to be eaten raw.
  • When travelling in countries where you are unsure of the water treatment and sanitation systems, avoid eating uncooked foods. Eat foods that have been thoroughly cooked and are still hot. Safe beverages include tea and coffee made with boiled water and carbonated bottled beverages with no ice. Avoid tap water, or ice made from tap water.

Is there anything special I need to know?

If you are diagnosed with Giardiasis and you provide services to others, particularly seniors or children, you should not go to work while you are experiencing symptoms. You should consult with your health care provider and employer to determine when it is safe for you to return to work.   

Protect others by not swimming if you are experiencing diarrhea. Avoid public recreational waters for 2 weeks after your symptoms have gone away. It is possible that even after you are feeling better you will still be shedding the parasite in your stool for a period of time. 

To prevent spreading the disease to people around you always practice good hand washing and hygiene.


For data on the incidence of Giardiasis in Simcoe Muskoka and Ontario, please visit the Giardiasis page on the health unit’s HealthSTATS site

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