For health professionals: Giardia infection (giardiasis)

Find detailed information on Giardia infection for health professionals.

On this page

What health professionals need to know about Giardia infection

Giardia is a parasite that occurs worldwide. The parasite is in the top 5 most common cases of infectious diarrheal diseases in Canada and can affect people of all ages.

Giardia is the most commonly identified intestinal parasite in Canada. The Canadian Notifiable Disease Surveillance System reported 10.42 cases of giardiasis per 100,000 people in 2015.

In developed countries, giardiasis occurs most frequently among:

Drinking untreated water is a common source of infection and can result in community-wide epidemics.

Giardia has a broad host range worldwide. However, many strains:

The role of animals as a source of human giardiasis is not well characterized. Some genetic groups of Giardia duodenalis infect both humans and other mammals. It is not known how frequently infection is transmitted from animal to human, or from human to animal. Animal sources have been described in a small number of outbreak investigations reported in the literature.

Clinical manifestations

The incubation period is from 7 to 14 days.

Most people with giardiasis will have some or all of the following symptoms:

Some people with giardiasis may present with no symptoms. Children up to 9 years old are most at risk. Most of the infections occur in the summer months.

Most infections resolve on their own within 1 to 2 weeks or longer.  For some cases, recurrence of symptoms can occur after several days or weeks.

More chronic infections can occur and result in malabsorption. As a result, significant weight loss may occur, as well as hypoalbuminemia and deficiencies in vitamins A, B12 and folate.


Multiple stool samples may be required to detect Giardia as the Giardia cysts can be excreted sporadically and can make diagnosis difficult.

Techniques for Giardia detection in stool include:


Dehydration should be treated symptomatically.

The following drugs can be used for treating giardiasis:


Health professionals in Canada play a critical role in identifying and reporting cases of giardiasis. Giardiasis was added to the notifiable disease list in 1983. Refer to the surveillance of giardiasis section for more information on surveillance in Canada.

For more information

Page details

Date modified: