Giardiasis can be transmitted by person-to-person spread by the faecal-oral route, by contact with the faeces of infected animals, by consumption of contaminated food or drink, waterborne including swimming in contaminated water, or by sexual transmission, particularly among men who have sex with men.

Many cases are associated with recent foreign travel, particularly from South Asia, and it is the most identified pathogen in returning travellers with prolonged diarrhoea.

Diarrhoea is the most common symptom of giardiasis. Other symptoms include abdominal cramps, bloating, flatulence, malaise, loss of appetite, and rarely nausea. Malabsorption, weight loss, and faltering growth may occur in children.

Suspected giardiasis

If giardiasis is suspected, especially if there is recurrent or prolonged diarrhoea (over 14 days) or travel to at-risk areas:

• Send up to three faecal specimens at least two days apart for testing.
  • If related to recent foreign travel, include travel destination on laboratory request form and specifically request ova, cysts, and parasites (OCP).

Advise all people with suspected or confirmed giardiasis infection about:

• Drinking enough fluids to avoid dehydration.
• Preventing the spread of infection (detailed information on personal hygiene, environmental cleaning, and disposal of soiled materials, can be found here)
  • Advise the person that they should not go swimming for 2 weeks after the last episode of diarrhoea.
• Seeking medical help if symptoms worsen rapidly or significantly at any time.
• Avoiding the use of antimotility drugs (such as loperamide) to treat diarrhoeal symptoms.
• A period of lactose intolerance may occur following giardiasis which may last several weeks.
  • Consider a lactose-free diet for one month after treatment followed by a gradual reintroduction when symptoms settle.

Following positive stool sample result

Notify the local health protection team immediately of confirmed giardiasis by completing a notification form.

Screen all household and sexual contacts for giardia as household members may have asymptomatic infection.

Metronidazole

• Adults and children over 10 years of age:
  • 2g once daily for 3 days, or 400mg 3 times a day for 5 days
• Children 1 to 9 years of age (doses given once daily for 3 days):
  • 1 – 2 years: 500mg
  • 3 – 6 years: 600–800mg
  • 7 – 9 years: 1g

See section: 5.1.11 Nitroimidazole derivatives

Alcohol should be avoided during and for at least 48 hours after metronidazole treatment, because of the possibility of a disulfiram-like reaction (flushing, abdominal cramps, vomiting, tachycardia).

If metronidazole is not appropriate or not tolerated seek specialist advice.

Pregnancy or breastfeeding

In the case of pregnancy or breastfeeding discuss with a microbiologist or infection specialist.

Treatment failure

Discuss compliance with metronidazole course, consider repeating metronidazole treatment as above if treatment course was not completed. If metronidazole is not appropriate or not tolerated seek specialist advice.

Recurrence or reinfection

If recurrence of symptoms occurs:

• Review screening:
  • Check all household and sexual contacts for giardia as household members may have asymptomatic infection.
  • Pets can be a source of giardia carriage so patients should consider discussing screening with their veterinarian.
• Consider repeating metronidazole treatment as above or seek specialist advice.
• Alternative unlicensed treatments may only be available from secondary care.