Epidemiology and transmission^[1][2]

Giardial infections occur worldwide, including in developed countries. It is more common with:

• Poor sanitation.
• Travel to endemic areas.
• Reduced immunity - malnutrition, immunocompromise or cystic fibrosis.
• Institutions, egchildren in nurseries and their carers.
• Those having ano-oral sex (eg sexually active gay men).

Incidence: in England and Wales there were around 3,000 cases per year identified (data from 2004-2006).^[3]

Worldwide prevalence: it occurs at any age but is common in young children, (estimated around 20% prevalence in young children in developing countries).^[4]

Transmission

• Giardia is transmitted via the faeco-oral route. The incubation period is 1-2 weeks.^[1] Giardial cysts are resistant to standard chlorination.
• Transmission is usually via contaminated drinking water.
• Other possible sources are ingested food, contaminated swimming pools, and direct contact with infected people, animals or contaminated objects.
• In the UK, many cases are associated with recent foreign travel.
• Many animals are host to the organism, including pets, livestock and wild animals, but it is not clear if they are a source of infection for man. Beavers may be an important reservoir host^[1] (in Canada, giardiasis is nicknamed 'beaver fever').

Presentation

Suspect giardiasis in scenarios such as:

• Acute diarrhoea lasting >1 week.^[5]
• Traveller's diarrhoea with symptoms lasting >10 days, symptoms that begin after return, and associated weight loss.^[6]
• Diarrhoea in immunocompromised or palliative care patients.^[2]

Symptoms:^[2]

• Acute or chronic diarrhoea.
• Malabsorption, weight loss and, in children, failure to thrive.
• Abdominal pain, anorexia, flatulence, bloating, and nausea.
• Vomiting and fever are uncommon.

Signs:

• Generally, there are few or no physical signs.
• In acute or severe cases, signs of dehydration or malnutrition.
• Physical examination generally is unremarkable.
• Abdominal examination may reveal nonspecific tenderness.

Unusual presentations:

• Rarely, may present with complications (see section on Complications and prognosis, below).

Investigations

Stool microscopy is the usual test:

• Ensure the lab request has a full history and a request for ova, cysts and parasites (OC&P). Note that the routine microbiological examination of a stool sample looks only for Campylobacter spp., E. coli O157, Salmonella spp., Shigella spp. and Cryptosporidium spp. Testing for other pathogens may be carried out depending on the clinical history.^[2]
• If parasitic infection is suspected, send three fresh specimens (5 ml each) 2-3 days apart, as OC&P are shed intermittently.^[2]
• About 60% of giardial infections are identified using a single sample, and >90% are identified after three stool examinations.^[1]

Other tests for giardiasis are:^[1]

• Stool antigen tests are available and may be the best test.
• DNA probes for Giardia spp. are available.
• Other tests: duodenal samples for microscopy can be obtained using the 'string test' (swallowing a gelatin capsule on a string) or duodenal biopsy.

Differential diagnosis

• Other causes of gastroenteritis, including cryptosporidiosis.
• Other causes of malabsorption, eg coeliac disease.
• Inflammatory bowel disease.
• Irritable bowel syndrome (if other problems excluded).

Management

General points:

• In areas where there is contamination of the water supply the treatment of asymptomatic patients is of dubious value, as they will become re-infected.^[1]
• Treatment is required where there are symptoms, or where there is risk of infection of others who are at special risk. Some authors suggest that in non-endemic areas everyone should be treated if found to be carrying the organism.^[1]
• Giardiasis may be caused by food poisoning and therefore can be a notifiable disease.

Drug treatment:

• Rehydration, if required.
• Metronidazole is the drug of choice for treating giardiasis^[2] - but note cautions with pregnancy and breast-feeding.^[7]
• Tinidazole is an alternative.^[2]
• Other possible treatments are mepacrine (unlicensed),^[7] mebendazole,^[8] quinacrine^[9] and chloroquine.^[10]

Complications and prognosis^[1]

Prognosis:

• The prognosis is usually good.
• Resistance to treatment or re-infection can occur.

Possible complications are:

• Failure to thrive (children) or malabsorption.
• Contributes to debility and malnutrition in developing countries, especially in children.^[11]
• Lactose intolerance.
• Occasionally, infective gastroenteritis may unmask other conditions, such as coeliac disease or inflammatory bowel disease, so persisting symptoms should be investigated.^[5][12]
• Rare complications include cholecystitis, reactive arthritis, pancreatitis, retinal arteritis, and iridocyclitis.
• Death from giardiasis is rare - usually from dehydration in those at high risk.

Prevention^[1]

• Handwashing and hygiene around infected people and in institutions.
• Chlorination, sedimentation, and filtration methods should be implemented to purify public water supplies adequately. Effective chlorine inactivation of giardial cysts in water requires optimal water treatment procedures, which may be difficult to achieve, especially in swimming pools.
• Travellers to endemic areas should avoid eating uncooked foods.
• Drinking water can be purified by using filtration (pore size, <1 μm) or by boiling water for >5 minutes.
• If other water treatments are not available, use chlorine or iodine water treatments - but these are less effective against giardia than boiling or filtration.
• Breast-feeding is protective.