Giardia infection

Giardia or giardiasis is caused by a group tiny parasites known as Giardia intestinalis or Giardia lamblia or Giardia duodenalis. Giardia is an infection of the gut. The infection can cause diarrhoea, nausea, and abdominal pain. It is common. It can cause problems even in healthy people.

Please note that vomiting and diarrhoea may also be symptoms of infections caused by Cryptosporidium and Norovirus.

Giardia does not always cause symptoms. Some people carry the parasite that causes Giardia without ever knowing it. When this happens a person is referred to as being asymptomatic. When symptoms do happen, they can include:

  • Diarrhoea that comes on suddenly and that can start off watery
  • Feeling generally unwell
  • Offensive smelling or fatty bowel movements
  • Abdominal cramps, wind, and bloating
  • Nausea or vomiting
  • Weight loss

These symptoms aren’t specific to giardia though and may occur with other gut infections and in patients with immunodeficiency when they have non-infectious gut involvement.

See your doctor or nurse if you:

  • Have severe diarrhoea, meaning it happens many times in a day
  • Have severe abdominal pain
  • Cannot eat or drink
  • Have a fever higher than 38°C

Young children and older adults with symptoms should make sure to see their doctor or nurse. That’s because these groups can get dehydrated more easily than other people.

Giardia infections can spread in 3 ways:

  • From person to person – The parasite that causes Giardia lives in bowel movements of people who are infected. You can catch Giardia from another person if they do not wash their hands after a bowel movement and then touch you. The same is true for someone who changes a nappy on a child or an adult and then does not wash his or her hands. It is also possible to catch Giardia through any kind of anal sex (even if you use a condom).
  • Through food – The parasite that causes Giardia can live on food. Cooking kills it. But if food is not cooked or not handled the right way, it can carry Giardia. Please read our food safety advice.
  • Through water – The parasite that causes Giardia can live in water sources that people drink from. For instance, Giardia can live in streams or drinking wells. People who camp and hike are at risk of getting Giardia if they drink water from lakes or streams without treating the water properly first.

Yes. If your doctor or nurse thinks you might have Giardia, he or she will ask you for a bowel movement sample. At the lab, the sample can be checked for Giardia and other infections that can cause the same symptoms as Giardia. A fresh stool sample is required though and it is often missed on a poorly kept specimen.

Treatment for Giardia involves taking an antibiotic medicine for several days. In most cases, that gets rid of the infection and its symptoms. In some cases, though, Giardia does not get better with the first round of antibiotics. If that happens, doctors usually suggest changing the type or dose of antibiotic, or increasing the length of time a person is treated.  This is particularly true for PID patients. Rehydration with oral rehydration salts following age specific recommendations is very important for individuals with significant symptoms.

Yes, it can. The most important thing is hygiene. Follow these tips:

  • Wash your hands with soap and water after using the bathroom, and teach children to do the same
  • Wash your hands with soap and water after changing nappies or after touching anyone who can’t control his or her bowels
  • Throw away dirty nappies right away in sealed trash bins
  • Wash clothes that could have even small amounts of bowel movement on them
  • Try not to swallow water when swimming
  • Kill the germs and parasites in your drinking water when travelling or hiking. You can do this by doing 1 of these things:
    • Boiling drinking water for at least 10 minutes at a hard boil
    • Adding 5 drops of tincture of iodine (you can buy this from your pharmacist) to 4 cups of water and waiting 30 minutes.
    • Using a good water filtering system (ensure the labelling indicates that it will remove parasites).

Yes and no. Because even in individuals with healthy immune systems Giardia can cause persistent infection, the best thing is avoidance.

In general terms:

Asymptomatic patients with immunodeficiency who show no symptoms of giardia infection will usually be encouraged to be treated and close family members tested.

  • Sometimes infection can persist in some patients with immunodeficiency despite adequate treatment but be reassured most patients do respond to standard therapy
  • Don’t spread the infection! If you know you have giardia follow the infection control guidance when visiting the clinic or hospital and if you are unsure ring ahead to check
  • Read our leaflet for more tips on staying healthy whilst away.

This information was reviewed by Dr Matthew Buckland, Chair of our Medical Panel, August 2022.