Family doctor



GIARDIA - a patient's guide


Giardia is caused by drinking contaminated water and can easily spread in day-care settings. This article looks at how to treat and prevent the illness.


  • Giardia is caused by a parasite
  • You mainly get it from drinking water contaminated with the parasite
  • It is the most common waterborne disease in developed countries
  • The illness causes diarrhoea, stomach pains, and possibly nausea and weight loss
  • Children in day care centres and people who drink untreated water are most at risk
  • Diagnosis involves examining feces collected over several days
  • Drug treatment is used to rid the body of the parasite
  • People can still be infectious for some weeks after they recover

What is it?

It is caused by a parasite called Giardia lamblia which lives in people's stomachs, causing diarrhoea and stomach pains.

Giardia is mainly caused by drinking contaminated water, or food that has been washed in contaminated water. It is now recognised as one of the of the most common waterborne diseases in the developed world.

Epidemics of the illness have been reported in areas with contaminated drinking water, with the Sydney outbreak the most dramatic in recent times.

Outbreaks are more common in institutional settings like day care centres. Travellers and campers who drink untreated water are also more at risk.

The parasite is spread from infected feces of humans or animals contaminating food or water. The infection can be picked up by drinking contaminated water supplies, and touching objects like toys and bathroom doors that may been in contact with the parasite, and then touching your mouth.

Sexual transmission is also possible.

What are the symptoms?

Diarrhoea, stomach pains and feeling nauseous are the main signs of Giardia, although some people may not notice anything wrong.

The infection can lead to weight loss and dehydration.

The symptoms usually begin within two weeks of eating or drinking contaminated food or water. But some people have it for nearly four weeks before showing signs of infection.

Diagnosis involves laboratory testing of stools that have been collected over several days.

What can be done to help?

Antibiotic treatment (e.g. metronidazole, or similar antibiotics) is used to rid the body of the parasite, but treatment failure is common.

Symptoms last up to six weeks in most cases, but some people can take longer to recover. People may be infectious for several weeks after they have recovered.

In people without diarrhoea and other symptoms, treatment may not be necessary.

How can it be prevented?

Avoid drinking water that has not been properly treated.

Always wash your hands after going to the toilet and before handling food.

Dispose of sewage waste carefully.

Do not drink unboiled water while camping or travelling. Do not eat uncooked foods that may have been washed in contaminated water.

Sex partners may also need to be examined for any sign of the infection.

Young children with Giardia need to be kept home from day care centres until they have recovered.

Getting help

Your doctor will be able to help diagnose and treat the condition.

See also:

Did this article meet your requirements/expectations?