CHOLERA

Last updated: 06 September 2004

1. Reason for surveillance

• To identify the source of infection, stop transmission and fulfil international cholera reporting requirements.

2. Case definitions

A confirmed case of cholera requires laboratory definitive evidence.

Laboratory evidence
Isolation of toxigenic Vibrio cholerae O1 or 0139.

Clinical Evidence
Not applicable

Epidemiological Evidence
Not applicable

Factors to be considered in case identification
Laboratory diagnosis of cholera involves isolation of toxigenic V. cholerae serogroups O1 or O139 from a clinical specimen such as stool or vomitus. Special media are required. The laboratory should be notified if a patient with diarrhoea has recently returned from overseas.

Note that cholera is subject to the Commonwealth Quarantine Act (1908).

3. Notification criteria and procedure

Cholera is to be notified by:

• Hospital CEOs on clinical diagnosis (ideal reporting by telephone on same day of diagnosis)

• Laboratories on microbiological confirmation (ideal reporting by telephone on same day of diagnosis).

Only confirmed cases of toxigenic V. cholerae serogroup O1 or O139 should be entered onto NDD.

Note that cholera is subject to the Commonwealth Quarantine Act (1908).

4. The diseases

Infectious agent
The toxigenic bacillus Vibrio cholerae, serogroups O1 and O139.

Mode of transmission
Cholera is transmitted by ingestion of food, particularly seafood or water contaminated with faeces or vomitus of infected persons.

Most cases reported in NSW are acquired in developing countries. Rarely, infection may be acquired from local sources such as contaminated rivers (especially in northern NSW and Queensland), and imported foods.

Timeline
The typical incubation period is from a few hours to 5 days, usually 2 to 3 days.

Cholera is presumed to be infectious while stools are positive for V. cholerae, which is usually only a few days after recovery. Occasionally a carrier state may persist for several months.

Clinical presentation
The usual clinical presentation is characterised by a sudden onset of profuse watery diarrhoea, occasional vomiting and dehydration. Asymptomatic and mildly ill cases are common, especially among children.

5. Managing single notifications

Response times
Investigation
On same day of notification of a probable or confirmed case begin follow-up. Notify CDB of the case's age, sex, onset date, and likely time and place of acquisition by email. CDB will forward these data onto the Commonwealth.

Data entry
Within 1 working day of notification enter confirmed cases on NDD.

Response procedure
The response to a notification will normally be carried out in collaboration with the case's health carers. But regardless of who does the follow-up, PHU staff should ensure that action has been taken to:

• Confirm the onset date and symptoms of the illness

• Confirm results of relevant pathology tests, or recommend the tests be done

• Find out if the case or relevant care-giver has been told what the diagnosis is before beginning the interview

• Seek the doctor's permission to contact the case or relevant care-giver

• Review case and contact management

• Identify likely source.

Case management
Investigation and treatment
Refer to Therapeutic Guidelines: Antibiotic for specific treatment. Maintaining fluid and electrolyte balance is important. Ensure that the laboratory sends the V. cholerae isolate to ICPMR for typing.

Education
The case or relevant care-giver should be informed about the nature of the infection and the mode of transmission. Emphasise the importance of hygienic practices, particularly hand washing before eating and preparing food and after going to the toilet. Linen and towels used by the case should not be shared, and should be washed separately in hot water.

Isolation and restriction
Strict isolation of cases is not necessary, provided good hygiene is observed.

Cases who are food handlers or care for young children or the elderly or debilitated are required not to attend work until their stools are negative for V. cholerae.

Environmental evaluation
If available, samples of any residual food or water suspected from the epidemiological investigation should be collected for laboratory analysis. If a septic tank has become contaminated, disinfection may be required.

Contact management
Identification of contacts
Persons at risk of infection are those who shared food or drink with an infectious case, or those who have eaten from an implicated food source.

Identification and treatment
Investigation
Stool culture from contacts is recommended. Contact should be advised to seek medical attention and report to the PHU if symptoms develop in the 5 days after last exposure to an infectious case or implicated source.

Passive immunisation
None

Active immunisation
Active immunisation with cholera vaccine is of little practical value for contacts of cases.

Antibiotic prophylaxis
May be considered if there is a high likelihood of secondary transmission within households. See Therapeutic Guidelines: Antibiotic.

Education
Advise susceptible contacts (or parents/guardians) of the risk of infection; counsel them to watch for signs or symptoms of cholera occurring within 5 days of exposure to an infectious case or contaminated source.

Isolation and restriction
None