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Public Health - Seattle & King County


Giardia lamblia is a protozoan widely found in nature. It is transmitted by ingesting food or water contaminated with the feces of infected mammals especially beavers, puppies, and cats, and sometimes humans. Fecal-oral transmission can occur in child-care centers, households, and during sexual contact. Child-care center outbreaks have been associated with toddler wading pools where diapered children share the same water. Like other enteric infections, rates of giardiasis increase during warmer months, probably because of more frequent exposure to contaminated water through swimming or camping. Travelers to developing countries are at increased risk of giardiasis as well.

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Giardiasis in King County

Purpose of surveillance:

  • To identify outbreaks and potential sources of ongoing transmission.
  • To prevent further transmission from such sources.

Cryptosporidiosis case data

Local epidemiology:

In 2012, 174 cases of giardiasis were reported. Beginning in early 2011, laboratories were required to report positive results for giardia, resulting in an increase in reports compared to past years. National surveillance guidelines were also updated, eliminating the reporting of giardiasis in asymptomatic persons (many of whom were immigrants and recent international adoptees who had screening tests performed upon arrival to the U.S.).

Six cases reported hospitalization, and none died. Twenty-six (15%) cases reported recent international travel, with an additional three cases occurring among persons recently relocating to the United States from residences abroad. Among international travelers, 10 cases had traveled to Asia and the South Pacific, five to South and Central America, four to Mexico, two to Europe, two to Africa and one each to the Caribbean, Australia and New Zealand, and the Middle East. Due to limited resources, individual giardiasis cases do not receive telephone interviews, but are sent a mail-in questionnaire and fact sheet with information about giardiasis. During 2012, 83 (48%) cases returned their questionnaires with information about possible sources of infection.

Each year in Washington state there are between 400 to 600 cases reported.