Reviewed August 2017
Giardiasis is an infection caused by the parasite Giardia lamblia (G. lamblia). When this parasite is swallowed it can cause a diarrheal illness. The parasite lives in the intestines of infected humans and animals and is passed in the stool. Once in the environment, it can survive for a long time. Giardiasis occurs around the world and is more common in children than adults.
People get infected by eating, drinking or putting something into their mouth that is contaminated with the stool of an infected person or animal. The parasite can be found in soil, food, water and on surfaces or hands that have been contaminated with the stool of infected humans or animals. People can be exposed by drinking contaminated lake or river water, by touching your mouth after touching contaminated surfaces such as bathroom handles, changing tables, diapers and toys or by oral-anal contact during sex with someone who is infected.
Some people can be infected and not have any symptoms. For those who do get sick, symptoms may include:
Symptoms can start between 3 and 25 days after you become infected, but usually start after 7 to 10 days. Symptoms can last for 1 to 6 weeks.
The signs and symptoms of giardiasis are similar to other stomach infections. Giardiasis can be confirmed through lab testing of stool samples. Multiple stool samples may be required to detect the parasite.
If you have symptoms, your healthcare provider may recommend antibiotics. It is important to drink extra fluids if you have diarrhea to prevent dehydration. For people without any symptoms, treatment is generally not required.
Most people fully recover without complications. People who are immune deficient, have HIV or have had previous gastric surgery are at higher risk of more severe disease. Severe giardiasis can cause damage to the lining the intestine and painful swelling of the joints (reactive arthritis). Infants and pregnant women are more likely to experience dehydration from diarrhea caused by giardiasis.
Anyone who is infected with giardiasis should stay at home while they have symptoms and until at least 24 hours after the symptoms have gone away. It is important that food handlers, those who provide healthcare services, those who work or attend a childcare centre and those who come into contact with water as part of their job (e.g., swimming pools, hot tubs or water parks) stay home and away from work or daycare until at least 24 hours after their symptoms have gone away.
There are a number of steps you can take to protect yourself and those around you:
Giardiasis is a reportable communicable disease. Individuals living in Ontario who test positive for giardiasis must be reported to their local health department by either the lab or their healthcare provider. Toronto residents infected with giardiasis will be contacted by Toronto Public Health to get additional information to determine the source of the infection. This information can be helpful in ensuring that contaminated food or water does not cause illness to other people.
Call Toronto Public Health at 416-338-7600 (TTY at 416-392-0658) or speak to your healthcare provider.