What it is

Giardiasis is an infection of the digestive system caused by tiny parasites about one hundredth of a millimeter in size known as Giardia intestinalis (also known as ‘Giardia lamblia or Giardia duodenalis). The parasites live in the intestines of humans and animals. In most cases, the infection is caught from other humans.

How is it spread?

While inside the intestines, the parasites form a hard protective shell known as a giardia cyst. When an infected person goes to the toilet, some of the cysts can be passed out of the body inside faeces. Giardia cysts can survive outside the body for several weeks or months. Once outside the body, giardiasis can be spread in many ways such as:

  • Drinking water that has been contaminated with infected faeces
  • Direct contact between infected and non-infected people
  • When an infected person does not wash their hands properly after going to the toilet and transfers the parasites on to surfaces, utensils or food
  • Parents or childcare workers who change the nappy of a baby with giardiasis have an increased risk of developing the condition by accidentally transferring faeces into their mouth. This risk is generally higher in places where there are many babies and frequent nappy changing, such as day care centers and nurseries
  • Sexual activity that involves contact with another person’s back passage (anus)
  • Swimming in contaminated water (e.g. lakes and rivers)
  • Hikers and campers who drink contaminated water from streams and lakes
  • Eating or drinking in parts of the world where standards of water hygiene are poor.


Many individuals may not present with symptoms as the infection is usually cleared by the immune system. When this does not occur, symptoms come on 1-2 weeks after the first contact with the parasite. Symptoms of giardiasis infection can be:
a) Sudden onset or acute symptoms of diarrhoea
b) Persistent or chronic symptoms of diarrhoea
Other symptoms include:

  • abdominal cramps
  • bloating, flatulence and belching that may be foul-smelling
  • nausea
  • indigestion and loss of appetite
  • weight loss often due to malnutritionfatigue
  • dehydration
  • Vomiting
  • A mild fever of 37°-38°C (98.6-100.4°F)

Preventing giardiasis

Giardiasis can be prevented by practicing good hygiene.
Hand washing is the most important thing you can do to prevent infection.
When travelling to areas of poor sanitation avoid:

  • Drinking tap water or water that has not been boiled or chemically treated, even if it looks clean. This includes drinking water from rivers and lakes
  • Eating ice cubes/ice cream, shellfish, mayonnaise, eggs, salads, raw or undercooked meats, fruit that has already been peeled
  • Swimming in water that may be contaminated with giardia (e.g. lakes and rivers). Swimming pools and water parks can sometimes become contaminated, particularly if they are used by young children.

Prevention of Spread

If you are or anyone you are caring for is, infected with giardiasis:

  • Wash your hands thoroughly with soap after using the toilet, changing a nappy and before preparing, serving or eating food
  • Do not share towels or flannels
  • Stay away from work, school or college for at least 48hours after the last episode of diarrhoea and/or vomiting. Avoid contact with other people as far as possible during this time
  • If you have anal sex, make sure you use a condom and wash your hands after handling a used condom. Kissing or licking also increases the risk of infection and should be avoided
  • If you handle food on a regular basis, you must inform your employer if you develop symptoms of vomiting and/or diarrhoea, and immediately leave the food-handling area
  • If you work with vulnerable groups of people such as the elderly, unwell or the young, you should inform your employer if you develop symptoms


Giardiasis infection can be treated as follows:

  • With antibiotics as prescribed by your GP
  • With adequate fluids to prevent dehydration
  • If you are able to keep fluid and foods in, eat small light meals and avoid fatty, spicy or heavy foods
  • Paracetamol and ibuprofen may help to ease high temperature or headache

For further information, contact the Infection Prevention and Control Department at St Bernard’s Hospital
Telephone: 20072266 Ext 2315