Giardiasis Outbreaks — United States, 2012–2017

Abstract

Giardiasis is a diarrheal disease caused by the parasite Giardia duodenalis, the most common cause of intestinal parasite infections in the United States. Transmission occurs when Giardia cysts spread from feces to water, food, surfaces, or skin and are then ingested. Illness is characterized by gastrointestinal symptoms, including diarrhea, abdominal cramps, greasy stools, bloating or gas, nausea, vomiting, weight loss, and dehydration. Approximately 50% of infections are asymptomatic (1,2). Most symptomatic Giardia infections are self-limited in duration; however, some persons might experience a reoccurrence of symptoms or develop long-term complications (3). During 2012-2017, public health officials from 26 states reported 111 giardiasis outbreaks (760 cases) to the National Outbreak Reporting System (NORS). Three main modes of transmission for these outbreaks were identified: water exposure in 29 (26%) outbreaks, person-to-person contact in 28 (25%) outbreaks, and contaminated food in six (5%) outbreaks. A single transmission mode could not be determined in 48 (43%) of the outbreaks. Private residences and child care facilities were the most common settings of outbreaks for all the transmission modes combined. To prevent and control giardiasis outbreaks, CDC recommends prompt diagnosis, maintaining good hand hygiene, cleaning and disinfecting home environments and child care facilities, and monitoring water quality in private wells.