Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures | Additional sources of information

Victorian statutory requirement

Cryptosporidial infection (Group B disease) must be notified in writing within five days of diagnosis.

School exclusion: exclude cases from child care and school until diarrhoea has ceased or until a medical certificate of recovery is produced.

Notification is required if Cryptosporidium spp are isolated from water supplies.

Infectious agent

Cryptosporidium parvum is a coccidian protozoon.

Identification

Clinical features
Cryptosporidiosis is a parasitic infection that commonly presents as gastroenteritis. Enteric symptoms usually include watery diarrhoea associated with cramping abdominal pain, bloating, vomiting and fever. The disease is usually mild and self-limiting. In persons with impaired immunity, particularly those with AIDS, it may be prolonged and life-threatening. Cryptosporidiosis infection may less commonly involve the lungs (bronchitis or pneumonia), gall bladder (cholecystitis) or pancreas (pancreatitis). Symptoms usually last four to twenty-one days.

Method of diagnosis
As tests for Cryptosporidium are not routinely conducted in some facilities laboratories should be informed if cryptosporidiosis is suspected.

Oocysts may be identified by microscopy of faecal smears treated with a modified acid-fast stain. A monoclonal antibody test is useful for detecting oocysts in faecal and environmental samples.

Oocyst excretion is most intense during the first days of illness. Oocysts are rarely recovered from solid faeces.

ELISA assays have been developed for the detection of antibodies but these are not in routine use.

Incubation period

The incubation period is estimated to be one to twelve days, with an average of seven days.

Public health significance & occurrence

Cryptosporidiosis occurs worldwide. Young children, the families of infected persons, men who have sex with men, travelers, health care workers and people in close contact with farm animals comprise most reported cases. Substantial outbreaks linked to public water supplies have been reported in the United States. Multiple outbreaks associated with public swimming pools and spas have been reported in Australia and worldwide. The risk of infection for Melbourne residents has been greater for people exposed to public swimming pools and household contacts of infected persons.

Reservoir

Reservoirs include humans, cattle and other domestic animals.

Mode of transmission

Transmission occurs by the faecal-oral route (person to person and animal to person), and via ingestion of contaminated foods and water.

Period of communicability

Cases may be infectious for as long as oocysts are excreted in the stool. Asymptomatic excretion may persist for several weeks after symptoms resolve.
Under suitable conditions oocysts may survive in soil and be infective for up to six months.

Susceptibility & resistance

Everyone is susceptible to infection. People with normal immune systems usually have asymptomatic or self-limited gastrointestinal disease.

People with impaired immunity may experience prolonged illness.

Control measures

Preventive measures
Encourage good personal hygiene, particularly following contact with animals or infected persons. Particular attention to hand washing is required during calving seasons on cattle properties.

Filter or boil contaminated drinking water, as chemical disinfectants such as chlorine are not effective against oocysts at the concentrations used in water treatment.

Control of case
Treatment is symptomatic and particularly involves rehydration. Antibiotics are not indicated.

Exclude symptomatic persons from food handling, direct care of hospitalised and institutionalised patients and care of children in child care centres until asymptomatic.

Disinfect soiled articles.

As oocyst excretion may persist for extended periods it is not advisable for cases to swim in public pools for a period of two weeks after their diarrhoea has ceased.

Control of contacts
The diagnosis should be considered in symptomatic contacts.

Control of environment
Faecal contamination of pools requires prompt action by the pool operator including disinfection, but oocysts resist standard chlorination. Refer to the Department of Human Services’ Pool operators’ handbook.

Outbreak measures

An outbreak investigation is required if two or more cases are clustered in a geographic area or institution. Investigate potential common sources such as contact with farm animals, consumption of contaminated water or unpasteurised milk or exposure to a common recreational swimming area.

The Department of Human Services considers cases may be linked to a public swimming facility if two or more people with Cryptosporidium infection (confirmed by a pathology laboratory) have used the same pool within two weeks of their illness. In this situation pool owners may need to close the affected swimming pool until it has been treated and superchlorinated with at least 14 mg/L free chlorine for at least 12 hours.

It is important to ensure that the total chlorine level in a treated pool is less than 8 mg/L before re-opening it to the public. If an outbreak is particularly large, the Department may request additional steps to be undertaken.

Additional sources of information

Victorian Department of Human Services 2000, Pool operators’ handbook