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Cryptosporidial diarrhoea

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Cryptosporidiosis is a diarrhoeal disease caused by Cryptosporidium, a microscopic protozoan parasite

  • Cryptosporidium may infect humans and animals
    • the parasite lives in the intestines of infected humans and animals
    • an infected person or animal sheds a high quantity of Cryptosporidium oocysts in the feces
  • Cryptosporidium hominis (previously known as C. parvum Type 1) and Cryptosporidium parvum (previously known as C. parvum Type 2) are primarily responsible for morbidity and outbreaks of disease
    • in addition, HIV-infected patients may be affected by Cryptosporidium meleagridis, Cryptosporidium felis, and Cryptosporidium canis

In the UK:

  • Cryptosporidium is the commonest protozoal cause of acute gastroenteritis
  • C parvum infections peak in spring and C hominis peaks in late summer and autumn
  • number of cases in the first half of the year have reduced while in the second half, the number remains high (2)

The infection is commonly seen in young children (especially under the age of 5 years) but may affect healthy person of any age. However majority of clinical problems are seen in those with advanced immunosuppression.

  • substantial morbidity is seen in the developing world and with children who are malnourished (including those with apparently asymptomatic infection who may exhibit poor growth)

Asymptomatic carriage of the organism has also been reported (2).

  • a study carried out in day care centres for young children reported that unusual genotypes of Cryptosporidium were found proportionately much more frequently in asymptomatic carriers than in patients with symptomatic disease (2)

Summary (3):

Cause: Cryptosporidium, a protozoan parasite. C.hominis and C. parvum cause most laboratory confirmed cases in the UK. Species are determined by reference genotyping

Reservoir: Gastrointestinal tracts of humans and animals.Asymptomatic carriage has been documented in humans and animals

Epidemiology: One of the most common protozoal causes of gastroenteritis in the UK


  • Approximately 40% of laboratory confirmed cases occur in children below 5 years of age. Most cases are acquired within the UK; approximately 20% report recent foreign travel
  • Ingestion of oocysts
  • Faeco-oral spread:
    • Direct or indirect contact with infected animals
    • Person to person spread, particularly in households, healthcare and nurseries
    • Water contaminated directly or indirectly with faeces
    • Outbreaks have been associated with public and private water supplies, swimming pools and, more rarely, contaminated food. Seasonal outbreaks are associated with farm visits to feed and handle lambs and calves

Incubation period:

  • Incubation period is dose dependent. Usual range 3 – 12 days (usual median 5-7 days)


  • Whilst symptomatic and for up to 2 weeks after symptoms have stopped

Notes (3):

  • immunocompromised individuals (particularly people with profound T cell immunodeficiencies) are at increased risk of experiencing severe/prolonged symptoms and of complications. Complications may be severe and life threatening, and may include pancreatitis, sclerosing cholangitis and biliary cirrhosis (rare) or pneumoretroperitoneum / pneumomediastinum (very rare)
  • clinicians treating immunocompromised cases should seek expert advice
  • laboratories may not routinely test for Cryptosporidium species so prompt microbiological diagnosis should be discussed with routine diagnostic laboratories
  • oocysts are highly resistant to disinfection with levels of chlorination usually used in drinking water treatment and swimming pools.


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