Notification requirement for cholera
Cholera is an ‘urgent’ notifiable condition and must be notified by medical practitioners and pathology services immediately by telephone upon initial diagnosis (presumptive or confirmed). Pathology services must follow up with written notification within 5 days.
Cholera is subject to Australian quarantine.
This is a Victorian statutory requirement.
Infectious agent for cholera
Cholera is an acute diarrheal illness caused by infection of the intestine with the bacterium Vibrio cholerae.
There are more than 200 V. cholerae serogroups; however, only the toxigenic stains of serogroups O1 and O139 are predominantly associated with cholera and cholera epidemics. Occasionally, other serogroups of V. cholerae are associated with sporadic cases but are not spread in the epidemic form.
Non-O1 vibrios, formerly known as non-agglutinable vibrios or non-cholera vibrios, are now included in the species V. cholerae, but the reporting of non-O1 or non-O139 infections as ‘cholera’ is inaccurate and may be confusing.
Most non-O1, non-O139 strains do not secrete enterotoxin but can cause sporadic disease. There is no evidence that non-O1, non-O139 strains are involved in epidemics. ‘Non-toxigenic Vibrio cholerae’ refers to cases of cholera-like illness caused by organisms other than the O1 and O139 V. cholerae species. Those infections are not notifiable. The non-notifiable V. cholerae can cause gastroenteritis, wound infections and bloodstream infections, especially in immunosuppressed individuals, and are most often associated with exposure to brackish water.
Identification of cholera
Cholera infection is most often asymptomatic or results in mild gastroenteritis. Approximately one in 20 people will have severe disease, with profuse painless, watery diarrhoea described as ‘rice water stools’ and vomiting leading to rapid volume depletion. Rapid loss of fluid can lead to dehydration; signs and symptoms include loss of skin turgor, dry mucous membranes, hypotension and thirst. Additional symptoms include muscle cramps, which are secondary to electrolyte imbalance. Without treatment, shock can rapidly lead to death. The case-fatality rate may exceed 50 per cent without treatment but is less than 1 per cent with appropriate rehydration treatment.
The diagnosis is confirmed by the isolation of V. cholerae serogroup O1 or O139 from faeces. A presumptive diagnosis can be made by visualisation by darkfield or phase microscopy of V. cholerae’s characteristic spiral motility, specifically inhibited by preservative-free serotype-specific antiserum.
Incubation period of Vibrio cholerae
The incubation period is from a few hours to 5 days; it is usually 2–3 days.
Public health significance and occurrence of cholera
Cholera can occur in epidemics or pandemics. In any epidemic, one particular biovar tends to predominate.
Endemic cholera occurs in large parts of Africa and Asia and intermittently in areas of South America, the Middle East, Central and Eastern Europe and Oceania. Cholera appears to be increasing worldwide in both the number of cases and their distribution. Cholera is rarely seen in Australia (two to six cases per year, usually in individuals infected in endemic areas).
Occasional cases are acquired through exposure to water in northern Australia. V. cholerae O1 is established in the riverine environment in some parts of Queensland and New South Wales; however, human disease is rare.
Reservoir for Vibrio cholerae
V. cholerae is often part of the normal flora of brackish water, such as in estuaries, and can be associated with algal blooms (plankton). Humans are one of the reservoirs of the pathogenic form of V. cholerae.
Mode of transmission for Vibrio cholerae
Transmission occurs through the ingestion of contaminated water or food. Sudden large outbreaks are usually caused by a contaminated water supply. Outbreaks and endemic and sporadic cases are often attributed to raw or undercooked seafood. Direct person-to-person transmission is rare.
Period of communicability of cholera
People are infectious while symptomatic and for a few days after recovery. Occasionally, the carrier state may persist for months, with chronic biliary infection and intermittent shedding of organisms in the stool for many years. The bacterium can survive in a wide variety of foods and drinks for 1–14 days at room temperature and for 1–35 days in an icebox. It has also been found on fomites at room temperature for 1–7 days.
Susceptibility and resistance to cholera
Children and older people are most at risk of infection. Even in severe epidemics, clinically apparent disease rarely occurs in more than 2 per cent of those at risk. Gastric achlorhydria (the absence of hydrochloric acid in the gastric secretions of the stomach) or other causes of high gastric pH increase the risk of disease. There is some evidence that breastfeeding reduces the risk of infection.
Infection results in a rise in antibodies with increased resistance to reinfection.
Infection with an O1 strain does not confer immunity against O139 strains; nor does infection with an O139 strain confer immunity against O1 strains.
Control measures for cholera
Travellers to endemic areas should be advised about careful food and water consumption and personal hygiene. They should carry oral rehydration solution, which is available from pharmacies.
Cholera vaccine is an inactivated whole-cell V. cholerae O1 in combination with a recombinant cholera toxin B subunit (rCTB) containing inactivated Inaba, Ogawa, classic and El Tor strains. It provides partial protection (approximately 50 per cent) for 6 months and possibly longer in adults. It is not routinely recommended, and advice to overseas travellers should emphasise the careful selection of food and water rather than immunisation.
Vaccination should be considered for people at increased risk of diarrhoeal disease, including those with achlorhydria, poorly controlled or complicated diabetes, inflammatory bowel disease, HIV/AIDS, other conditions resulting in impaired immunity, or significant cardiovascular disease.
Vaccination is not an official requirement for entry into any foreign country.
Control of case
The Chief Human Quarantine Officer in Victoria is notified of all confirmed cases of cholera.
Prompt fluid therapy with adequate volumes of electrolyte is critical, as life-threatening dehydration may occur rapidly. This is usually all that is required for mild to moderate illness. Patients with severe dehydration require urgent intravenous fluid. Antimicrobial agents to which the strain is sensitive shorten the duration of diarrhoea and reduce the volume of rehydration solutions required and the duration of Vibrio excretion. Antibiotic-resistant strains of V. cholerae are now common in some regions. In the event of treatment failure, antibiotic prescribing should be guided by microbiological susceptibility data. See the Therapeutic guidelines: antibiotics.
Investigate possible sources of infection, such as the consumption of shellfish, particularly if there is no history of travel to an endemic region.
Control of contacts
Contacts who have shared food or water should be observed for 5 days from the date of last exposure. This may include all the fellow travellers of a case. Stool culture of any contacts with symptoms of diarrhoea and all household contacts, even if asymptomatic, should be undertaken. Cases should also be looked for among those possibly exposed to a common source. The immunisation of contacts is not indicated.
Control of environment
Severely ill patients should be isolated in hospital with standard and contact precautions for diapered or incontinent people for the duration of illness.
Less severe cases can be managed at home. Cleaning and disinfection of linen and articles used by the patient are required. Terminal cleaning and disinfection of hospital rooms and equipment are required.
In cases with no history of overseas travel, the urgent investigation of potentially contaminated food and water supplies is indicated.
Outbreak measures for cholera
A single case of cholera in a person with a history of no overseas travel is considered an outbreak. Initiate a thorough investigation to determine the vehicle and circumstances of transmission, and plan control measures accordingly. Educate the population at risk about the need to seek appropriate treatment without delay. Adopt emergency measures to assure a safe water supply. Ensure the careful supervision of food and drink preparation.
The immunisation of contacts is not indicated, even in an epidemic.
Reporting of cholera to the World Health Organization is mandatory under international health regulations. This will be done by the Australian Government Department of Health.