Giardiasis is an intestinal infection caused by a protozoan and is spread by contaminated water or contact with an infected person. People who are travelling or hiking should assume water sources are contaminated and either purify drinking water or drink bottled water. Healthcare or daycare workers should practice good hygiene when going from person to person. Unprotected anal sex can also transmit Giardiasis from an infected person to the partner.
Review Date 3/4/2020
Updated by: Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.