National case definition: Giardiasis

Date of last revision/review: December 2023.

National notification

Only confirmed cases of disease should be notified.

Type of surveillance

Routine case-by-case notification to the federal level.

Case classification

Confirmed case

Laboratory confirmation of infection with or without clinical illness from an appropriate clinical specimen (e.g., stool, intestinal fluid, small bowel biopsy), with demonstration of:

• Giardia lamblia trophozoites and/or cysts;
  or
• Giardia lamblia nucleic acid (e.g., by polymerase chain reaction (PCR) or other nucleic acid test (NAT));
  or
• Giardia lamblia antigen (e.g., by an immunologic assay).

Probable case

Clinical illness in a person who is epidemiologically linked to a confirmed case.

Laboratory comments

Untreated and unfixed (i.e., without formalin) clinical specimens are recommended for PCR and deoxyribonucleic acid (DNA) based methodologies including molecular diagnostic testing and downstream molecular surveillance approaches. Formalin-based fixatives used for microscopy can interfere with nucleic acid detection and sequencing.

Note: For molecular surveillance purposes, Cary Blair transport media is acceptable.

Clinical evidence

Clinical illness may be characterized by the following signs or symptoms: Diarrhea, abdominal pain, nausea, bloating, weight loss, fatigue, gas, dehydration, and/or malabsorption. The severity of illness may vary. Asymptomatic infections may occur.

ICD code(s)

ICD-11 code(s)

• 1A31 Giardiasis

ICD-10 code(s)

• A07.1 Giardiasis (lambliasis)

Comments

Probable case definitions are provided as guidelines to assist with case finding and public health management, and are not for national notification purposes.