Reviewed August 2017

What Is Giardiasis?

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.

How Is Giardiasis Spread?

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.

What Are the Symptoms of Giardiasis Infection?

Some people can be infected and not have any symptoms. For those who do get sick, symptoms may include:

  • Diarrhea
  • Frequent pale and greasy stools
  • Bloating
  • Abdominal Cramps
  • Weight Loss
  • Dehydration

How Soon After Exposure to the Parasite Do Symptoms Usually Begin?

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.

How Do I Know That I Have Giardiasis?

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.

How Is Giardiasis Infection Treated?

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.

What Are the Possible Complications of Giardiasis?

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.

Are There Any Restrictions for People with 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.

What Can Be Done to Prevent the Spread of Giardiasis?

There are a number of steps you can take to protect yourself and those around you:

  • Thorough hand washing is the best prevention. Since the parasite is passed in stool, the single most important prevention activity is careful hand washing after using the washroom, handling diapers, before and after preparing food and before eating.
  • Clean and sanitize diaper changing areas after each use.
  • Do not prepare food for others if you have diarrhea.
  • Peel fruits and vegetables, or wash with uncontaminated or bottled water before eating.
  • Drink water that you are certain has been properly treated and not directly from rivers, creeks and lakes. Do not swallow recreational water.
  • If treated or bottled water isn’t available, boil water for at least one minute. The boiled water should be used for drinking, brushing teeth, making ice cubes, washing uncooked fruits and vegetables, cooking and washing dishes.
  • Avoid contact with stool during sex.
  • Do not swim in recreational water (e.g., swimming pool, hot tub) until at least 24 hours after symptoms have gone away.

What Is the Role of Toronto Public Health in Investigating Giardiasis?

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.

More Information

Call Toronto Public Health at 416-338-7600 (TTY at 416-392-0658) or speak to your healthcare provider.