Cryptosporidiosis

Queensland Health Guidelines for Public Health Units

Revision history

Infectious agent

Cryptosporidiosis is a predominantly enteric disease caused by protozoan parasites belonging to the genus Cryptosporidium. From among the more than 40 identified species, two species, C. hominis and C. parvum, are thought to be responsible for more than 95% of human infections⁽¹⁾.

Cryptosporidium species have a monoxenous life cycle completed within the gastrointestinal tract of a single host⁽²⁾. In humans, following ingestion of infectious thick-walled oocysts, excystation occurs with the release of infective sporozoites that adhere to and invade the epithelial cells of the small intestine. Within these cells the parasites undergo asexual and then sexual multiplication, followed by fertilisation. The subsequent zygote may give rise to either environmentally resistant thick-walled oocysts which are excreted from the host in faeces, or thin-walled oocysts that excyst endogenously resulting in ongoing autoinfection of the host⁽³⁾.

The infectious dose for cryptosporidiosis is low, with <10 C. hominis or C. parvum oocysts able to cause infection⁽⁴⁾. An individual can excrete as many as 5 x 10⁷ oocysts per 1mL of faeces⁽⁵⁾.

In Queensland (Qld) Cryptosporidium speciation is not routinely performed by diagnostic laboratories, placing some limitations on the public health understanding of sources of infection.

Case definitions and notification criteria

Only confirmed cases should be notified.

Confirmed case

A confirmed case requires laboratory definitive evidence only.

Laboratory definitive evidence

1. Detection of Cryptosporidium oocysts by direct microscopy in a faecal specimen.
2. Detection of Cryptosporidium specific antigen.
3. Detection of Cryptosporidium by Nucleic Acid Test (NAT).

Outbreak criteria:

Common source: Two or more cases epidemiologically linked to a common source by location and time of exposure.

OR

Community-wide: A generalised, community-wide increase in observed case numbers versus expected case numbers.

Notification procedure

Pathology laboratories to notify on pathological confirmation, by usual means.

Objectives of surveillance

1. To identify outbreaks of cryptosporidiosis and enable a timely public health response.
2. To monitor the epidemiology of cryptosporidiosis.

Public health significance and occurrence

Cryptosporidium spp. are ubiquitous and globally significant causes of gastrointestinal disease⁽⁶⁾. Internationally, risk factors for sporadic infections include recent travel, immunocompromising conditions, contact with other cases, contact with contaminated recreational waters, consumption of untreated drinking water, animal contact, and consumption of foods including raw milk and poorly washed fruits and vegetables^(7,8). Australian research into sporadic cryptosporidiosis risk has shown that swimming in public pools and contact with a person with diarrhoeal illness carries increased risk⁽⁹⁾.

Australia

Cryptosporidiosis is a nationally notifiable condition, with a notification rate in 2023 estimated at 13.8 cases per 100,000 population⁽¹⁰⁾. Annual notification rates tend to fluctuate in Australia, with peaks generally seen every three to five years. There are also marked geographic and demographic variations in disease, with warmer and more remote regions having higher disease incidence⁽¹¹⁾.

Queensland

Qld consistently records higher numbers of Cryptosporidium infections than elsewhere in Australia. In 2023, the Qld rate was 26.2 cases per 100,000 population, approximately twice the national rate^(10,12). In 2024, Qld recorded 6,178 Cryptosporidium notifications, the highest annual total ever reported, equating to a rate of 110.6 cases per 100,000 population^{(OzFoodNet Qld)}.

International comparisons

Australian and Qld notification rates are markedly higher compared to similar high-income settings, with both the European Union and the United States (US) reporting notification rates <3.0 cases per 100,000 population^(13,14). Recently, Australian and Qld rates have surpassed those of New Zealand (11.9 per 100,000 population), which has been recognised as having among the highest rates in the world ⁽¹⁵⁾.

Outbreaks

In Qld, outbreaks have been linked to settings such as childcare centres, public aquatic facilities (including swimming pools and water play areas), and the consumption of unpasteurised milk ^{(OzFoodNet Qld, 16)}. In both Europe and the US, large outbreaks linked to contamination of public water supplies have resulted in substantial morbidity and considerable public concern ^{(17, 18)}. In contrast, no outbreaks linked to public drinking water supplies have been reported in Australia.

Clinical features

Cryptosporidiosis typically presents as an acute gastroenteritis, with the main symptom being watery diarrhoea, frequently accompanied by abdominal pain, anorexia, weight loss nausea, vomiting, fatigue and low-grade fevers ⁽¹⁹⁾. Illness is generally self-limiting with a median duration of 9-15 days. However, symptoms can persist for up to a month among otherwise healthy persons ⁽¹⁹⁾. Asymptomatic infection has also been described ⁽²⁰⁾.

Symptom relapse, due to autoinfection, is reported in up to a third of cases ^{(3, 7)}. Among particular immunocompromised groups (see Susceptibility), there is some risk of chronic, intractable diarrhoea, in addition to hepatobiliary complications ⁽²⁰⁾.

Respiratory cryptosporidiosis is a less commonly reported presentation, with oocyst transmission postulated as occurring via inhalation of aerosolised droplets or by contact with contaminated fomites ⁽²¹⁾.

Reservoir

Cryptosporidium spp. can be found in a variety of hosts including humans, cattle, and other domesticated and wild animals. C. hominis and C. parvum are the species most frequently associated with human intestinal infections, although both differ in their host range. The reservoir for C. hominis is humans, which it exclusively infects, while C. parvum has an infectious cycle that involves both humans and ruminants, predominantly cattle ⁽²²⁾.

Mode of transmission

Transmission generally occurs via the faecal-oral route. Ingestion of oocysts may occur through:

• Ingestion of contaminated recreational water. This is a primary mode of transmission, with well-recognised exposure sources that include swimming pools and other public aquatic facilities ^{(5, 9, 23)}.
• Direct (or indirect) person-to-person contact. This has been demonstrated through the increased risk of infection among close contacts of confirmed cases, particularly among younger children and their care providers ^{(9, 24, 25)}.
• Direct zoonotic transmission. This is well recognised, given knowledge of animal reservoirs, particularly livestock ⁽¹⁾. Both direct and indirect contact with animals during visits to farms, petting zoos and animal nurseries carry increased risk ^{(26, 27)}.
• Consumption of contaminated food. Foodborne infection is much less common, but has been linked to consuming fruits and vegetables washed in contaminated water and drinking unpasteurised milk ⁽⁷⁾.
• Sexual transmission. While less frequently documented, oral-anal contact carries increased risk, particularly among men who have sex with men ⁽²⁸⁾.
• Inhalation (or ingestion) of aerosolised oocysts. This has been postulated as a means of transmission underpinning respiratory cryptosporidiosis ⁽²¹⁾.

Incubation period

Variable; a likely range of 1-12 days, with an average of 7 days ⁽²⁹⁾.

Period of communicability

Oocysts appear in stools at the onset of symptoms and may be excreted for up to 60 days after cessation of gastrointestinal symptoms ⁽³⁰⁾. Oocysts have been reported to survive outside of the human body for 2–6 months or longer ⁽³¹⁾, but their viability is subject to complex environmental considerations, including temperature, humidity, precipitation, soil composition and water characteristics ^{(32, 33)}. Notably, oocysts are resistant to standard levels of chlorine disinfection in swimming pools and can remain viable for over a week in swimming pools ⁽³⁾.

Susceptibility

While young children and immune-compromised persons carry an intrinsically higher risk of developing infection, susceptibility is universal. Some immune-compromised cases may experience chronic, intractable diarrhoea, or otherwise complicated disease, with the potential for fatal outcomes. Those most at risk include patients with T-cell immune deficiencies, haematological malignancies and advanced / late diagnosed HIV infections ⁽²⁰⁾.

Management

Cases

Investigation

Routine case investigation is at the discretion of the public health unit but is generally not indicated unless there is suspicion of a cluster or outbreak.

Restriction

Enteric precautions are to be applied during acute illness. Exclude all cases who are food handlers, or carers of children or patients until at least 48 hours after diarrhoea has ceased. Thorough handwashing after defecation should be stressed. Due to the potential for prolonged excretion of oocysts, persons with cryptosporidiosis should not enter a swimming pool until 14 days after symptoms have ceased.

Evidence of microbiological clearance is not required.

Treatment

Treatment is supportive only with a focus on maintaining fluid and electrolyte balance. There is no drug registered for the treatment of cryptosporidiosis in Australia. However, the antiprotozoal nitazoxanide may be prescribed as a Category C medicine under the Therapeutic Goods Administration Special Access Scheme, ⁽³⁴⁾ noting clinical trial data shows nitazoxanide has limited efficacy in the treatment of children and immune-compromised individuals ⁽³⁵⁾.

Counselling

If a case investigation is undertaken, advice should be provided about the mode of transmission and personal interventions, with emphasis on handwashing and avoidance of swimming pools and aquatic facilities.

Contacts

Contact tracing

Contact tracing and contact management is generally not indicated.

Definition

Persons who have had close contact with a confirmed case.

Investigation

The contacts of sporadic cases are not usually investigated but can be provided with hygiene education, and advice to seek medical attention should they develop symptoms. Stool cultures from asymptomatic contacts may only be necessary for situations where the spread of infection is particularly likely, e.g. child-care centres or swim schools.

Restriction and Counselling

If identified, symptomatic contacts should be excluded from food handling and caring for children or patients until investigated, or their symptoms cease.

Community clusters and outbreaks:

• Investigate to determine the source, including water, food and animal contacts.
• Investigate common exposures to possible sources, e.g. child-care centres, swimming pools, contact with farm animals.
• When two or more cases are epidemiologically linked to a swimming pool or other aquatic facility, the relevant public health unit should ensure that the facility is assessed in accordance with the Queensland Health Water quality guidelines for public aquatic facilities.
• Outbreaks and suspected outbreaks should be notified to OzFoodNet using the standard outbreak reporting template.

Other control measures and the environment

Faecal contamination of public swimming pools requires prompt action by the pool operator, including hyperchlorination. The oocyst’s small size (4-6µm) make them resistant to standard chlorination and conventional pool filters (which are not typically designed for oocyst removal) ⁽³⁶⁾, thus an operator of an affected swimming pool may need to close the pool until it has been treated in accordance with the departmental guidelines (see Other resources section). PHUs should liaise with the relevant local government to provide advice and support for pool closure and to ensure water treatment is undertaken correctly, as required.

In other settings, ensure that cleaning and disinfecting of surfaces and objects, including bathrooms and toilets, nappy change areas, food preparation areas, tabletops, highchairs, and toys is undertaken.

Preventive measures

Preventive measures against infection and practices to prevent ongoing transmission include:

• Avoid use of swimming pools and other aquatic facilities (e.g. splash pads and water play parks) during diarrhoeal illness and until 14 days after diarrhoea ceases.
• Avoid ingestion of recreational waters, including from swimming pools and other aquatic facilities and water bodies like dams, lakes, creeks or rivers.
• Avoid drinking untreated or inadequately filtered (non-potable) water from rain-water tanks, bores, dams, lakes, creeks or rivers.
• Avoid drinking unpasteurised milk.
• Wash raw fruits and vegetables with treated water prior to consumption.
• Wash hands thoroughly with soap and running water:
  • before handling or eating food
  • after handling animals
  • after toileting
  • after assisting children with toileting or changing nappies
  • upon children’s arrival to childcare
  • after gardening or direct contact with soil/animal manure.
• Practice safe sex, with abstinence recommended until 14 days after diarrhoea ceases.
• Avoid sharing linen and towels during diarrhoeal illness and until 14 days after diarrhoea ceases.

N.B. Alcohol-based hand sanitisers cannot inactivate Cryptosporidium oocysts and are not an appropriate substitute to handwashing with soap and running water⁽³⁷⁾.

Outbreak summary

Complete an outbreak summary form for OzFoodNet.

Other resources

Cryptosporidiosis | Health and wellbeing | Queensland Government

Water quality guidelines for public aquatic facilities (PDF 2363 kB)

References

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