Factsheet on Cholera

Cholera

Cholera is an acute intestinal infection caused by the bacterium Vibrio cholerae. It is caused by the O1 and O139 serogroups of V. cholerae which produce a toxin, and this is responsible for the clinical symptoms associated with the disease. Other serogroups exist, however these do not produce the disease known as cholera. Between 12 and 25 laboratory confirmed cases of cholera are diagnosed each year in England and Wales and all are travel associated infections.

Transmission

Cholera is spread through the faeco-oral route, mainly through drinking water contaminated by faeces. Food, especially shellfish, may also be a source of infection. Large epidemics occur in countries lacking safe drinking water and adequate facilities for the disposal of sewage.
Person-to-person transmission of cholera is rare without contamination of food or water. This is because the infectious dose, i.e. the number of bacteria that need to be ingested to cause disease, is high. The infectious dose for cholera ranges from one million bacteria in certain foods to over one billion bacteria in contaminated water. With a normal standard of personal hygiene it is very difficult to pass on millions of bacteria through personal contact or via surfaces. However, drinking water can become contaminated to such high levels following faecal contamination in areas where infection is introduced into the community and the water supply infrastructure is poor.

Symptoms

The incubation period (period from infection until symptoms occur) is usually 24-72 hours (limits: minimum 2 hours to maximum 5 days). However this does depend on the dose, i.e. the number of bacteria ingested.  Around 75% of people infected will not develop any symptoms and of those who do experience symptoms, only a small proportion develop severe disease. Those who do get symptoms rather than disease usually experience an abrupt onset of diarrhoea, which is watery and brown at first, but quickly changing to large volumes of pale fluid stools ('rice-water stools'). Fever is not a prominent feature of illness. In severe cases continuous fluid loss can quickly lead to extreme dehydration and shock, which in the most severe cases can be rapidly fatal. The severity of the disease experienced depends in part upon the general health and nutritional state of the patient, as well as the dose of organisms received. Most of the imported cases that have been reported in England and Wales over the last twenty years have been of mild to moderate disease.

Diagnosis

In epidemic situations most diagnoses are made clinically. In the UK diagnosis is by microbiological examination. Clinical suspicion for cholera should be high for anyone presenting in the UK with a diarrhoeal illness that has a history of having been in an area affected by a cholera outbreak or epidemic. Specimens should be immediately sent to the laboratory for testing along with any relevant travel history.

Treatment

The most important aspect of treatment for cholera is to ensure that fluid lost is replaced. Oral rehydration is usually successful in over 90% of cases, and rapid fluid replacement with a balanced solution of sugar, electrolytes and water (oral rehydration salts) should be started urgently. Intravenous fluids are required for severely dehydrated patients who cannot tolerate oral administration, and very large initial volumes may be needed e.g. 4-6 litres. Adequate hydration to replace fluid lost should continue while diarrhoea persists. The patient usually recovers spontaneously once the dehydration has been corrected. In some cases antibiotics may be used if the disease is very severe or prolonged, or if the patient is elderly or debilitated. The antibiotics normally used are tetracycline or ciprofloxacin.

Prevention and control

The most important measures in controlling the spread of cholera are the provision of safe drinking water and the sanitary disposal of human faeces. Travel and trade restrictions between countries are not effective.
To prevent transmission within the UK, standard enteric precautions should be used for patients with toxigenic cholera and if severely ill they should normally be admitted to an Infectious Disease Unit. Patients should also be reminded of standard personal hygiene measures. Because of the large infectious dose required, cholera is not easily transmitted in countries with functioning sanitary systems unless there is gross contamination of foods or drinking water. No evidence of person-to-person spread in England and Wales has been identified from a review of the data collected over the last twenty years and all of the cases in the database were attributable to travel associated infection.
Although it is unusual, occasionally a patient who has had cholera may continue to excrete organisms after they have recovered (i.e. no longer have diarrhoea). Repeat microbiological examination should therefore be done on recovered patients and if persistent carriage is detected a short course of antibiotics will usually eradicate the organism.

Patients who are food handlers should not return to work until 48 hours after the first formed stool and where indicated, two consecutive negative stools taken at intervals of at least 24 hours apart. Cholera is a statutorily notifiable disease and any confirmed or suspected cases should be reported to the local proper officer.

Last reviewed: 12 December 2008