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Dublin Boil Notice health explainer: What are cryptosporidiosis and giardiasis, what are the symptoms and how can they be prevented?






PEOPLE from the Greater Dublin Area are warned that if they drink contaminated tap water, they may suffer from diarrhoea and stomach cramps for up to two weeks.

Following the Boil Water Notice, which is affecting more than 600,000 people, the HSE have said that water produced at the Leixlip Treatment Plant may contain cysts of cryptosporidium and giardia. 

These may cause gastrointestinal infections with symptoms such as diarrhoea and stomach cramps lasting from one to two weeks. 

To raise awareness of the consequences of drinking contaminated water, the HSE have issued a detailed summery on cryptosporidiosis and giardiasis.


What is cryptosporidiosis?

Cryptosporidiosis is a diarrhoeal disease caused by a microscopic parasite (Cryptosporidium). Once an animal or person is infected, the parasite lives in the intestine and passes in the stool. The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very resistant to chlorine-based disinfectants. It can survive temperatures greater than 70oC. It is found (particularly in water) through the world.

How is cryptosporidiosis spread?

Cryptosporidium lives in the intestine of infected humans or animals. Millions of parasites can be released in a bowel movement from an infected human or animal. It is therefore found in soil, food, water, or surfaces that have been contaminated with human or animal faeces. It is a common cause of waterborne outbreaks of gastroenteritis. 

What are the symptoms of cryptosporidiosis?

The most common symptom of cryptosporidiosis is watery diarrhoea. Other symptoms include:


Weight loss

Stomach cramps or pain



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Some people with cryptosporidiosis will have no symptoms at all.

How long after infection do symptoms appear?

Symptoms of cryptosporidiosis generally begin 2 to 10 days (average 7 days) after becoming infected with the parasite.

How long will symptoms last?

In persons with healthy immune systems, symptoms usually last about 1 to 2 weeks. The symptoms may go in cycles in which you may seem to get better for a few days, then feel worse again before the illness ends. It is a mild disease in healthy people. It is often more severe in small children and elderly people and can be very serious in those people who are immunocompromised (such as patients undergoing cancer treatment, those living with HIV). 

If you have cryptosporidiosis, how do you limit spread to other people?

Cryptosporidium can be quite contagious. These simple measures will reduce the likelihood of spread:

Wash your hands with soap and water after using the toilet, changing nappies, and before eating or preparing food.

Do not swim in recreational water (pools, hot tubs, lakes or rivers, etc.) if you have cryptosporidiosis and for at least 2 weeks after diarrhoea stops. Cryptosporidium can be spread in a chlorinated pool because it is resistant to chlorine.


What is giardiasis?

Giardiasis is a form of gastroenteritis, characterised by diarrhoeal illness that is caused by a microscopic parasite, Giardia lamblia. 

How is giardiasis spread?

G. lamblia lives in the intestines of humans and many animals. Giardiasis occurs when the parasites are ingested, most commonly when contaminated water containing the parasites is drunk. Contaminated water may come from lakes or ponds, swimming pools, contaminated drinking water or ice. It may also be passed if the contamination is on food and environmental surfaces. It is resistant to the level of chlorination in drinking water.

What are the symptoms of giardiasis?

Symptoms occur between 7-10 days (usually 1-3 days) after exposure to giardia. Symptoms include:


foul smelling greasy stools



Diarrhoea can be prolonged leading to temporary malabsorption. Many cases are asymptomatic.

How is giardiasis diagnosed?

Diagnosis is based on finding giardia cysts in the stool of patients. Three samples are often needed as it may take three sets of stools to identify the parasite. 

What is the treatment for giardiasis?

Antibiotics are effective against giardia. 

How can spread of giardiasis be prevented?

Any person who has been diagnosed with giardiasis should practice scrupulous hand hygiene at home and in work as giardia can be readily passed between people. People can return to work once their bowel motions have been solid for 48 hours.

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