In many people, there are no symptoms of giardiasis following infection. It is estimated that, in the developing world, around 1 in 5 young children have giardial infection. Those most at risk of infection include travellers to areas where giardia is common (countries with poor sanitation), young children, men who have sex with men, and people with weakened immune systems for whatever reason. In 2017, 4,793 cases of giardia were reported in England and Wales.

It is the most common gut (intestinal) parasite infection in the UK. However, it can also be found in the developed world and outbreaks have occurred in day centres and institutions. As a living thing that lives in, or on, another living organism (a parasite), it is very commonly found in countries where sanitation is poor. Giardial infection is a common cause of infective diarrhoea throughout the world. It can also be caught by a person swimming in contaminated water (for example, in lakes, rivers, or swimming pools). Sexual activity involving contact with another person's back passage (anus) is another way of acquiring giardial infection. Spread within families in this way is also common. This means of transmission of infection is particularly common in young children. The parasite can then enter through your mouth and infect your small intestines. When you come into contact with that person, they can pass the parasite on to your hands.

For example, the infected person may have the parasite on their hands after going to the toilet. This is known as faecal-oral transmission of the infection. You may also become infected with giardia through direct contact with someone who has giardia. If there are deficiencies in water filtration, or if there is sewage contamination of water, giardial infection can be transmitted. Giardia are not killed by standard chlorination of drinking water. Transmission is often via contaminated drinking water containing the parasite. If water, food or drinks are contaminated by the infected faeces, giardia can be passed on to others. How do you catch giardia? From contaminated waterĪn infected individual will pass out the giardia in their stools (faeces).

Parasite infection symptoms in children