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NOTE: A surveillance case definition is a set of uniform criteria used to define a disease for public health surveillance. Surveillance case definitions enable public health officials to classify and count cases consistently across reporting jurisdictions. Surveillance case definitions are not intended to be used by healthcare providers for making a clinical diagnosis or determining how to meet an individual patient’s health needs.

CSTE Position Statement(s)

  • 09-ID-34

Clinical Description

An illness caused by the protozoan Giardia lamblia and characterized by diarrhea, abdominal cramps, bloating, weight loss, or malabsorption. Infected persons may be asymptomatic.

Laboratory Criteria For Diagnosis

  • Demonstration of G. lamblia cysts in stool, OR
  • Demonstration of G. lamblia trophozoites in stool, duodenal fluid, or small-bowel biopsy, OR
  • Demonstration of G. lamblia antigen in stool by a specific immunodiagnostic test (e.g., enzyme-linked immunosorbent assay)

Case Classification


A clinically compatible case that is epidemiologically linked to a confirmed case


A case that is laboratory confirmed


The 1997 case definition appearing on this page was re-published in the 2001 CSTE position statement 2001-ID-08 and the 2009 CSTE position statement 09-ID-34.1 Thus, the 1997, 2002, and 2010 versions of the case definition are identical.


  1. CDC. (1997). Case Definitions for Infectious Conditions Under Public Health Surveillance. MMWR, 46(RR-10), 1-55.

Related Case Definition(s)