Cholera and its treatment

Definition:

Cholera is an acute intestinal infection caused by ingestion of food or water contaminated with the bacterium Vibrio cholerae. It has a short incubation period, from less than one day to five days, and produces an enterotoxin that causes a copious, painless, watery diarrhoea that can quickly lead to severe dehydration and death if treatment is not promptly given. Vomiting also occurs in most patients.

Infectious agent

Vibrio cholerae serogroups O1 or O139 cause cholera.

Identification

Clinical features

Asymptomatic infection with V. cholerae is more frequent than clinical illness and bacteria may be present in faeces for 7–14 days. Mild cases of diarrhoea are common especially among children. In severe cases disease is
characterized by a sudden onset of symptoms with profuse painless watery (rice water) stools, occasional vomiting, rapid dehydration, acidosis and circulatory collapse. In untreated cases, death may

occur in a few hours and the case fatality rate may exceed 50%.

Method of diagnosis

The diagnosis is confirmed by the isolation of V. cholerae serogroup O1 or O139 from faeces. A presumptive diagnosis can be made by visualization by dark field or phase microscopy of V. cholerae’s characteristic motility, specifically inhibited by preservative-free serotype-specific antiserum.

Incubation period

The incubation period is from a few hours to five days. It is usually two to three days.

Public health significance and occurrence

Cholera can occur in epidemics or pandemics. In any single epidemic one particular biovar tends to predominate. Endemic cholera occurs in parts of Africa, Central Europe and Asia. Cholera appears to be increasing worldwide in both the number of cases and their distribution. Only sporadic imported cases in returned travellers occur in Victoria. V. cholerae O1 is established in the riverine environment in some parts of Queensland and New South Wales however human disease is rare.

Reservoir

V. cholerae is often part of the normal flora of brackish water and 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

Transmission occurs person to person via respiratory secretions.

Period of communicability

Asymptomatic carriers may be an important source of infection. Symptomatic patients can carry the bacteria in the nasopharynx for months after illness.

Susceptibility and resistance

Transmission occurs through ingestion of contaminated water and food. Sudden large outbreaks are usually caused by a contaminated water supply. Direct person to person contact is rare.

Period of communicability

Persons are infectious during the acute stage and for a few days after recovery. By the end of the first week 70% of patients are non-infectious. By the end of the third week 98% are non-infectious. Occasionally the carrier state may persist for months and chronic biliary infection with intermittent shedding of organisms may last for years.

Susceptibility and resistance

Even in severe epidemics, clinically apparent disease rarely occurs in more than two per cent of those at risk. Gastric achlorhydria increases 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 and vice-versa.

Control measures

Preventive measures

Travellers to endemic areas should be advised on careful food and water consumption and personal hygiene. Travellers to endemic areas should carry oral rehydration powder available from pharmacies which must be reconstituted with boiled or sterilised water. Cholera vaccine is a heat-killed suspension of the Inaba and Ogawa serotypes of V. cholerae O1. It provides partial protection (approximately 50%) for

three to six months. It is not routinely recommended and advice to overseas travellers should emphasise careful selection of food and water rather tha immunisation. Officially, cholera vaccination certificates are no longer required by any country or territory. Unofficially, some countries may still require such a certificate, in which case a single dose of cholera vaccine would satisfy this requirement.

Control of case

Cholera is subject to quarantine conditions under the Commonwealth Quarantine Act 1908. Prompt fluid therapy with adequate volumes of electrolyte solution such as Gastrolyte is critical as life-threatening

dehydration may rapidly occur. 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 the duration of Vibrio excretion. Investigate possible sources of infection, particularly if there is no history of travel to an endemic region.

Control of contacts

Contacts should be observed for five days from the date of last exposure. This may include all fellow travellers of a case. Stool culture of any contacts with symptoms of diarrhoea and stool culture of all household contacts, even if asymptomatic, should be undertaken. Cases should also be looked for among those possibly exposed to a common source. Immunisation of contacts is not indicated.

Control of environment

Severely ill patients should be isolated in hospital, with standard precautions. Less severe cases can be managed at home. Disinfection of linen and articles used by the patient is required. Faeces and vomitus can be disposed of into the toilet without preliminary disinfection, except in areas with an inadequate sewage disposal system. Terminal cleaning of hospital rooms and equipment is required. In cases with no history of overseas travel, urgent investigation of potentially contaminated food and water supplies is indicated.