Chapter reviewed and updated in December 2017. A description of changes can be found at Updates to the Communicable Disease Control Manual.


New Zealand Epidemiology

Children 1 to 4 years of age have the highest incidence rate for giardiasis in New Zealand.

More detailed epidemiological information is available on the Institute of Environmental Science and Research (ESR) surveillance website.

Further information on foodborne illness is available on the Ministry for Primary Industries website.

Case definition

Clinical description

An illness characterised by diarrhoea, abdominal cramps, bloating, flatulence, nausea, weight loss and malabsorption. The infection may be asymptomatic. Given the remitting/relapsing and variable nature of symptoms, the individual does not need to have compatible symptoms at the time of presentation but must have had a clinically-consistent illness in order to meet the case definition.

Laboratory test for diagnosis

Laboratory definitive evidence for a confirmed case requires at least one of the following from an appropriate gastrointestinal clinical specimen:

  • Giardia antigen detection by either:
    • detection of direct fluorescence using monoclonal antibodies
    • detection of antigens using a rapid antigen test
    • enzyme immunoassay
  • detection of giardia nucleic acid
  • visualisation by direct microscopy detection of giardia cysts or trophozoites.

Case classification

  • Under investigation: A case that has been notified, but information is not yet available to classify it as probable or confirmed.
  • Probable: A clinically compatible illness that either is a contact of a confirmed case of the same disease or has had contact with the same common source – that is, is part of a common-source outbreak.
  • Confirmed: A clinically compatible illness accompanied by laboratory definitive evidence.
  • Not a case: A case that has been investigated and subsequently found not to meet the case definition.

Spread of infection


Humans are the primary reservoir but wild and domestic animals such as cats, dogs and cattle can carry the infection.

Incubation period

Usually 3–25 days or longer; median 7–10 days.

Mode of transmission

Transmission occurs from ingestion of faecally contaminated food or drinking-water, swallowing recreational water (for example, swimming and wading pools, streams and lakes), exposure to faecally contaminated environmental surfaces, and person to person by the faecal-oral route.

Period of communicability

Throughout the entire period of infection, often months.


Notification procedure

Attending medical practitioners or laboratories must immediately notify the local medical officer of health of cases of probable or confirmed giardiasis.

See Appendix 5: Escalation pathways for more information

Management of case


Investigate and obtain a risk exposure history. Obtain a history of any possible contacts and travel, recreational water contact and consumption of untreated water.

Ensure laboratory confirmation by stool testing has been attempted.


In a health care facility, only standard precautions are indicated in most cases; if the case is diapered or incontinent, contact precautions should be applied for the duration of illness. For further details, refer to the exclusion and clearance criteria in Appendix 2: Enteric disease.

Cases should not use public swimming pools until 2 weeks after symptoms have resolved.


Advise the case and their caregivers of the nature of the infection and its mode of transmission.

Educate about hygiene, especially hand cleaning.

Management of contact


All people who have had close physical contact (for example, household) with a symptomatic case or who have been exposed to the same water, food or other material suspected to be the source of infection.


Investigate contacts who are symptomatic.


Contacts do not need to be excluded from work, school or other activities unless symptoms develop.


Not applicable.


Advise all contacts of the incubation period and typical symptoms of giardiasis, and to seek early medical attention if symptoms develop.

Other control measures

Identification of source

Check for other cases in the community. Investigate potential food and water sources of infection only if there is a cluster of cases or an apparent epidemiological link.

If indicated, check water supply for microbiological contamination and compliance with the latest New Zealand drinking-water standards (Ministry of Health 2008). Liaise with the local territorial authority staff to investigate potential water or pool sources of infection.


Clean areas and articles soiled with stools (for details, see Appendix 1: Disinfection).

Health education

Consider a media release and direct communication with relevant early childhood services, other institutions and health professionals to encourage prompt reporting of symptoms. In communications with doctors, include recommendations regarding diagnosis, treatment and infection control.

If a water supply is involved, liaise with the local territorial authority to inform the public. Advise on the need to boil water.

In early childhood services or other institutional situations, ensure satisfactory facilities and practices regarding hand cleaning; nappy changing; toilet use and toilet training; preparation and handling of food; and cleaning of sleeping areas, toys and other surfaces.

Educate the public about safe food preparation.

Hand-cleaning facilities should be available and used after contact with animals. Young children should be supervised during contact with animals and during hand cleaning. Food-related activities should be separated from areas that house animals. Domestic animals with diarrhoea should be taken to a veterinarian for assessment and treatment.


National reporting

Ensure complete case information is entered into EpiSurv.

Where food/food businesses are thought to be involved inform the Ministry for Primary Industries.

If an outbreak occurs, contact 0800GETMOH - CD option and outbreak liaison staff at ESR, and complete the Outbreak Report Form.

Further information


  • Ministry of Health. 2008. Drinking-water Standards for New Zealand 2005 (Revised 2008). Wellington: Ministry of Health.