Giardiasis (gee-ar-dye-a-sis) is an infection of the digestive system caused by tiny parasites called Giardia intestinalis (also known as Giardia lamblia, or Giardia duodenalis).

Diarrhoea is the most common symptom of giardiasis.

Other symptoms can include abdominal cramps, bloating and flatulence. Although these symptoms are often unpleasant, giardiasis doesn't usually pose a serious threat to health and can be easily treated.  

Read more about the symptoms of giardiasis.

When to see a doctor

See your GP if you have symptoms of diarrhoea, cramps, bloating and nausea that last for more than a week, particularly if you've recently travelled abroad.

Your GP may have to send some samples of your faeces to be tested in a laboratory to confirm a diagnosis of giardiasis. Up to three samples may need to be taken over a number of days to help ensure a correct diagnosis.

Giardiasis is usually treated successfully with antibiotic medicine that kills the giardia parasite. In most cases, medicines called metronidazole or tinidazole are used.

Read more about treating giardiasis.

How is giardiasis spread?

Most people become infected with giardiasis by drinking water contaminated with the Giardia parasite, or through direct contact with an infected person.

The giardiasis infection can also be passed on if an infected person doesn't wash their hands properly after using the toilet, then handles food that's eaten by others. Food can also be contaminated if washed with infected water.

Practising good hygiene – such as regularly washing your hands with soap and water – and taking care when drinking water in countries with poor levels of sanitation can help to reduce your risk of developing giardiasis.

Read more about the causes of giardiasis and preventing giardiasis.

Who is affected?

Giardiasis occurs almost everywhere in the world, but is particularly widespread where access to clean water is limited and sanitation is poor.

It can affect people of all ages but is most common in young children and their parents. This is because activities such as nappy changing increase the risk of infection.

There are more than 3,000 cases of giardiasis reported in England and Wales each year, although the true number is likely to be higher as many cases go undiagnosed.

Around one quarter of cases in the UK are thought to be contracted abroad, but many people don't develop the symptoms until they return home.

Most cases of giardiasis are one-off, but small outbreaks can sometimes occur in households, among family members, or at nurseries. Larger outbreaks are usually traced to contaminated water sources, such as drinking wells or water parks.

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