You are at risk for developing giardiasis if:

• You work in a day care center for young children, especially if many of the children are not yet toilet trained.
• You live in a household with young children.
• You swim in waters such as rivers, lakes, or streams, especially during the summer and fall months when the risk of exposure is greatest. The main risk is from swallowing water while swimming.
• You drink untreated or inadequately treated water, especially from rivers, lakes, or streams.
• You live or work in a nursing home or assisted living center or are a family member of an employee.
• You have oral-anal or oral-genital contact with an infected person.

Things that increase your chances of developing symptoms after infection include:

• Having an impaired immune system. Two disorders that affect the immune system and are especially known to increase the risk of giardiasis symptoms in children are common variable immunodeficiency and x-linked agammaglobulinemia.
• Having a condition that impairs intestinal function and makes the intestine more vulnerable to infection, such as inflammatory bowel disease or cystic fibrosis.
• Being malnourished before the infection.
• Having had stomach surgery.
• Taking medicines to reduce stomach acid if your stomach produces less acid than normal. (Stomach acid can kill some of the organisms.)