What is giardiasis?
Giardiasis is a form of gastroenteritis, characterised by diarrhoeal illness that is caused by a microscopic parasite, Giardia lamblia. Giardiasis is a notifiable disease in Ireland.

How is giardiasis spread?
G. lamblia lives in the intestines of humans and many animals. Giardiasis occurs when the parasites are ingested, most commonly when contaminated water containing the parasites is drunk. Contaminated water may come from lakes or ponds, swimming pools, contaminated drinking water or ice. It may also be passed if the contamination is on food and environmental surfaces. It is resistant to the level of chlorination in drinking water.

What are the symptoms of giardiasis?
Symptoms develop between 1 and 14 days (usually 7-10 days) following exposure to giardia. Symptoms include:

  • diarrhoea
  • foul smelling greasy stools
  • flatulence
  • nausea

Diarrhoea can be prolonged leading to temporary malabsorption. Many cases are asymptomatic.

How common is giardiasis?
Giardiasis is very common in certain parts of the world; in developing countries, between 2 and 7% of people shed cysts. In developed countries (including Ireland) most giardiasis occurs in young children. It is most often seen in toddlers who are not yet toilet trained and who spend a lot of time with other toddlers (such as in child care). Another group of people who are at risk are travellers to developing countries where water quality may be poor. It is known to be transmitted between gay men. Foodborne transmission is rare. In Ireland, there are between 60 and 70 cases notified each year. Up to date data on giardiasis can be found in our annual reports on giardiasis.  

How is giardiasis diagnosed?
Diagnosis is based on finding giardia cysts in the stool of patients. Three samples are often needed as it may take three sets of stools to identify the parasite. 

What is the treatment for giardiasis?
Antibiotics are effective against giardia. The antibiotic of choice is metronidazole.

How can giardiasis be prevented?
If you have been diagnosed as having giardiasis you should take any antibiotics prescribed by your doctor exactly as instructed i.e. finish the course. It is crucial that the person who has been diagnosed practices scrupulous hand hygiene at home (handwashing poster) and in work as giardia can be readily passed between people. People can return to work once their bowel motions have been solid for 48 hours.

Updated: 19 March 2024