Giardiasis is an intestinal infection that occurs due to a microscopic parasite known as Giardia lamblia. It can be spread by infected people via contact. Other than that a person can have giardiasis when he or she eat contaminated food or drink contaminated water. It is mainly occurred in small intestine and expels with stool in the form of cyst so that it can survive outside human body for several days. Giardiasis can be found all over the world, but people living in high populated area that don’t have good sanitary system and fresh water facilities can easily be infected with giardiasis.
Source: https://www.healthline.com/health/giardiasis