Cause: Protozoan Giardia lamblia, also known as G. intestinalis or G. duodenalis.

Illness and treatment: Infection may be asymptomatic or may cause diarrhea, abdominal pain, nausea, fatigue, and weight loss. Illness may be self-limited or be prolonged with persistent pale and greasy stools due to fat malabsorption. Anti-protozoal drugs are available.

Sources: Humans and both wild and domestic animals are reservoirs. Exposures include untreated surface water, shallow well water, recreational water, or less commonly food contaminated by feces. Person-to-person transmission occurs, such as in child care facilities, or by oral-anal sexual contact.

Additional risks: Children under 5 years of age are infected more frequently than adults. Concentrations of chlorine used in routine water treatment do not kill Giardia cysts, especially if the water is cold. Giardiasis is one of the most common waterborne diseases in the country.

Prevention: Wash hands thoroughly after contact with animals, particularly animals with diarrhea. Avoid swallowing water during water recreation. Do not drink untreated surface water. Boil untreated drinking water for one minute or use other appropriate water treatment.

Recent Washington trends: Reported cases have been declining somewhat over the past decade. Incidence is highest in the summer and fall months. Most frequently reported exposures include recreational water and international travel. Outbreaks are uncommon.

Purpose of Reporting and Surveillance

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

Legal Reporting Requirements

  • Health care providers and Health care facilities: notifiable to local health jurisdiction within 3 business days.
  • Laboratories: notifiable to local health jurisdiction within 2 business days; submission on request – within 2 business days.
  • Local health jurisdictions: notifiable to the Washington State Department of Health Office of Communicable Disease Epidemiology (CDE) within 7 days of case investigation completion or summary information required within 21 days.