Department of Health

Key messages

  • Giardiasis is not notifiable, but school and children’s services centres exclusions still apply.
  • Giardia infection is usually asymptomatic, but may present as acute or chronic diarrhoea.
  • Occurrence is worldwide, and it is endemic in most regions.
  • Giardiasis is detected more often in children than in adults, and children in childcare centres are particularly susceptible.
  • Waterborne outbreaks of giardiasis may occur as a result of faecal contamination of public water supplies or recreational swimming areas.

Notification requirement for giardiasis

Giardiasis is not a notifiable disease.

Primary school and children’s services centre exclusion for giardiasis

Exclude cases from school and children’s services centres until there has not been a loose bowel action for 24 hours.

Infectious agent of giardiasis

Giardia lamblia (G. intestinalis, G. duodenalis) is a flagellate protozoan found on surfaces, or in soil, food or water that has been contaminated with faeces from infected humans or animals. Most animal genotypes do not infect humans.

Identification of giardiasis

Clinical features

Giardia infection is usually asymptomatic, but may present as acute or chronic diarrhoea associated with abdominal cramps, bloating, flatulence, fatigue, anorexia, nausea and weight loss. Fat malabsorption may lead to steatorrhoea (the presence of excess fat in faeces).

Symptoms usually last 1–2 weeks or months. The rate of asymptomatic carriage may be high. Post-infectious lactose intolerance is common but self-limited.

Rarely, reactive arthritis has occurred after infection with Giardia.


Stool microscopy for cysts or trophozoites can be used for diagnosis of Giardia. However, a negative test does not preclude infection. The presence of erythrocytes or leucocytes in the stool is unusual in giardiasis. The diagnostic yield is increased if a second or third sample is also tested.

Tests using enzyme-linked immunosorbent assay (ELISA) or direct fluorescent antibody methods to detect antigen in the stool are more sensitive than direct microscopy, because Giardia cysts or trophozoites are not consistently seen in the stools of infected people.

Incubation period of Giardia

The incubation period is usually 3–35 days but may be longer. The average is 7–10 days.

Public health significance and occurrence of giardiasis

Occurrence is worldwide, and giardiasis is endemic in most regions. Infection is detected more frequently in children than in adults. It is readily transmitted in institutions such as childcare centres among children who are not toilet trained.

People at risk include:

  • children in childcare settings, especially diaper-aged children
  • people who care for, or live in a household with, people who are sick with giardiasis
  • international travellers to countries where Giardia is common
  • people who swallow water while swimming or playing in recreational waters where Giardia may live
  • people exposed to human faeces through sexual contact.

Reservoir of Giardia

Reservoirs include humans and animals, as well as contaminated waters.

Mode of transmission of Giardia

Anything that comes into contact with faeces from infected humans or animals can become contaminated with the Giardia parasite.

Transmission occurs from person to person and animal to person via hand-to-mouth transfer of cysts from infected faeces or faecally contaminated surfaces.

Waterborne outbreaks may occur as a result of faecal contamination of public water supplies or recreational swimming areas.

Period of communicability of giardiasis

Giardiasis is communicable for the entire period of cyst excretion, often months.

Susceptibility and resistance to giardiasis

Everyone is susceptible to infection. Relapses may occur.

Control measures for giardiasis

Preventive measures

Preventive measures include:

  • educating families and personnel of childcare centres in personal hygiene issues. This includes the need for hand washing before, during and after handling food; before eating; and after toilet use, changing nappies or cleaning a child who has used the toilet
  • protecting public and private water supplies against faecal contamination
  • educating travellers about the need for safe food and water consumption
  • minimising contact and contamination during sex.

Control of case

Symptomatic cases are usually treated with metronidazole, tinadazole or nitazoxanide. Nitazoxanide is available via the Special Access Scheme.

Consult the current version of Therapeutic guidelines: gastrointestinal.

Treatment of immunocompetent asymptomatic carriers is controversial.

Dispose of faeces in a sanitary and hygienic manner, and clean and disinfect soiled surfaces and articles.

Primary school and children’s service centres exclusion criteria apply until there has not been a loose bowel action for 24 hours.

Food handlers should not attend work until diarrhoea has ceased, and strict hygienic food preparation practices should be maintained.

Control of contacts

The diagnosis should be considered in symptomatic contacts. Active case finding among contacts is rarely indicated.

Control of environment

Disinfection of contaminated areas or water sources is required. Particular attention should be paid to potentially contaminated surfaces in childcare centres.

Outbreak measures for giardiasis

Two or more related cases may indicate an outbreak and require prompt reporting to the department. Attempt to identify a potentially common exposure, such as childcare attendance, or exposure to farm animals or recreational swimming areas. Epidemiological, environmental and laboratory investigations may be warranted as per the department’s Guidelines for the investigation of gastrointestinal illness.

Reviewed 29 November 2022


Contact details

Do not email patient notifications.

Communicable Disease Section Department of Health GPO Box 4057, Melbourne, VIC 3000

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