To identify the source of infection, stop transmission and fulfil international cholera reporting requirements.
Only confirmed cases should be notified.
A confirmed case requires laboratory definitive evidence only
Laboratory evidence
Isolation of toxigenic Vibrio cholerae O1 or 0139.
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.
3. Notification criteria and procedure
Cholera is to be notified by:
- Hospital CEOs on clinical diagnosis
- Laboratories on microbiological confirmation
All cases of V. cholerae should be entered onto NCIMS on the day of notification, toxigenic results are performed at the enteric reference laboratory, with results typically available within 3 working days after specimens are received.
4. The disease
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 particularly seafood that is eaten raw.
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.
Laboratory process in NSW
Vibrio species can grow on a wide variety of bacteriological media and specialised selective/differential media for Vibrio species. In NSW, laboratories do not routinely use specialised media for Vibrio species, unless the Vibrio culture is requested by the treating clinician, or by some laboratories if there is suspicion that the patient has cholera or vibriosis. A presumptive identification of the Vibrio species can be made from growth on differential media such as TCBS but will require confirmation using additional laboratory tests.
Vibrio bacteria can also be detected using nucleic acid tests (NAT) by laboratories that use gastrointestinal pathogen multiplex assays containing Vibrio species as one of the targets. A culture of the isolate from the primary sample will be required to identify the Vibrio species detected by the NAT and to differentiate between vibriosis and cholera. It is important to note that the NAT cannot discriminate between live and dead bacteria present in the sample.
If V. cholerae is identified the isolate must be sent to the enteric reference laboratory for further testing to establish if it is a toxigenic O1 and O139 serogroup.
5. Managing single notifications
Response times
Investigation
Within one day of notification of a possible* or confirmed case begin follow-up. Cases should be entered as a vibriosis case until typing and toxin results are available. It is likely that there will be some delay in toxin results, however case follow up should commence immediately.
*possible = Vibrio cholerae case pending toxin results.
Data entry
| Required data | Where to enter data in NCIMs |
| Clinical symptoms and onset date | Clinical package |
| Place of exposure/acquisition | Both in Clinical and Risk History packages |
| Seafood and water exposures | Risk History package
|
Within 1 working day of notification enter possible and confirmed cases on NCIMS. Update NCIMS with serogroup once available and change the condition type to Cholera. Non-toxigenic cases will remain as Vibriosis on NCIMS.
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:
Case management
Investigation and treatment
Treatment is managed of the diagnosing doctor. Maintaining fluid and electrolyte balance is important.
Ensure that the laboratory sends the V. cholerae isolate to ICPMR for typing and toxin testing.
Education
Inform the case or relevant caregiver about the nature of the infection and the mode of transmission. Emphasise the importance of hygienic practices, particularly hand washing before eating, preparing food and after using the toilet. Advise them not to share linen and towels used by the case and to wash these items separately in hot water.
Isolation and restriction
Cases who are food handlers and carers of patients, children and the elderly are required not to attend work until 2 stool specimens 24 hours apart are negative for V. cholerae.
Contact management
Identification of contacts
Persons at risk of infection are those who shared food or drink with an infectious case, travelled with the case or those who have eaten from an implicated food source.
Identification and treatment
Contacts 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.
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
6. Appendices