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Digestive health centre


Giardiasis is an infection of the digestive system caused by very small parasites called Giardia intestinalis, also known as Giardia lamblia, or Giardia duodenalis. These parasites can live in the intestines of humans and animals, and some people can carry the parasite without symptoms. In other cases it causes symptoms of intestinal infection, such as severe diarrhoea.

The parasite can be found in soil, food or water contaminated with the faeces of infected people or animals. Infection is acquired by taking in the cysts of the parasite from a contaminated source. The most common source of infection is contaminated water, but it can also be contracted directly from other people or from surfaces or items they have handled.

How common is giardiasis?

There are more than 3,500 cases of giardiasis reported in England and Wales each year. However, the actual number is likely to be higher as many cases are not diagnosed. About a quarter of the cases are believed to be contracted abroad, but the symptoms may not develop until the person has returned home.

What are the symptoms?

You won't necessarily know you have picked up the infection until the symptoms appear. The delay between getting the infection and the appearance of symptoms (the incubation period) is usually 7 to 14 days but may be as long as 45 days. The most common symptoms are:

You should seek medical advice if you have diarrhoea, cramps, bloating and nausea that last for more than a week, especially if you've recently been abroad.

If your baby or child has diarrhoea lasting for more than 2 or 3 days, or they've had 6 or more episodes of diarrhoea in the past 24 hours, or are showing signs of dehydration, seek medical advice.

Your GP may send stool samples to be tested in a laboratory to diagnose giardiasis. Up to 3 samples may need to be taken over a number of days to confirm the infection.

Who can get giardiasis?

Anyone can contract this infection. Those most at risk are:

  • People who drink water or eat food that is contaminated. There are countries where giardiasis is widespread because the food and water is often contaminated. High-risk areas include sub-Saharan Africa, Central and South America, some Asian countries, Russia, some Eastern European countries.
  • It can affect people of all ages but is most common in young children and their parents. This is because things like nappy changing increase the risk of infection. The risk is higher in places where there are many babies and frequent nappy changes, such as day care centres and nurseries.
  • People who have regular anal sex, because the giardia parasite can be passed from the anus (back passage) to the mouth.

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