Giardia duodenalis is an important source of gastroenteritis worldwide. Endemic cases have been described in developing and industrialized countries. We analyzed risk factors for sporadic giardiasis by a systematic review and a meta-analysis of the literature. From 72 studies, contact with an infected person, lack of personal hygiene, and attending a child daycare center were identified as risk factors in children and adults. Feco-oral transmission was significantly associated with exposure to human sewage/waste water, untreated drinking water and recreational waters. Travel abroad was a risk factor in industrialized countries. No handwashing before eating or preparing food, eating unwashed vegetables, or composite food were significant risk factors. Breastfeeding was a protective factor in developing countries. Interestingly, contact with pets was found as a significant risk factor in children in this meta-analysis. This could be explored in future studies with the comparison of the Giardia assemblage isolated from humans and pets. In the future, it would be interesting to investigate more precisely the type of water, vegetable, and whenever possible the method of preparation/treatment. Environmental and epidemiological investigations of specific risk factors by assemblages and types of Giardia spp. should be further studied. Finally, host factors in relationship with the severity and sequelae of giardiasis deserve future research.