Cholera

Cholera is an acute diarrhoeal disease caused by the infection of the intestine with the bacterium Vibrio cholera. Both children and adults can be infected and the disease remains a major public health problem. Acute watery diarrhoea is an illness characterized by three or more loose or watery (non-bloody) stools within a 24-hour period. Each year there are an estimated 1.3 to 4.0 million cases of cholera, including 21,000 to 143,000 deaths globally. Approximately 41 per cent of cases are reported from Africa, 37 per cent from Asia and 21 per cent from the Americas (data from 2015).

Primary causes include insufficient access to safe drinking water, proper sanitation and hygiene, and this impact can be exacerbated in areas where basic infrastructure is disrupted or has been destroyed. Countries facing complex emergencies and large population movements (of internally displaced persons [IDPs] or refugees) to overcrowded settings are particularly vulnerable to cholera outbreaks.

Most affected countries report an overall cholera case fatality rate (CFR) of greater than two  per cent. In some locations the CFR may approach 30—50 per cent in outbreaks where vulnerable groups have limited access to health care.

The following are standard case definitions to allow national health authorities to interpret data in an international context. However, during an outbreak case definition may be adapted to the local context and the Red Cross Red Crescent should use those agreed/established by national health authorities. NB: Consider that during community-based surveillance, volunteers should use broad (simplified) case definitions (referred to as community case definitions) to recognize most or all possible cases, provide relevant risk communication and appropriate actions and encourage them to seek care. Other actors such as healthcare workers or investigators studying the cause of a disease, on the other hand, can use more specific case definitions that may require laboratory confirmation.

Suspected case:

• In areas where a cholera outbreak has not yet been declared, any patient aged two years or older presenting with acute watery diarrhoea and severe dehydration or dying from acute watery diarrhoea.  
• In areas where a cholera outbreak is declared, any person presenting with or dying from acute watery diarrhoea.   

Note: It is important to note that children under two years are still affected by cholera and need to be treated immediately for acute watery diarrhoea and should be included in epidemiological data during outbreaks.

Confirmed case:

• Vibrio cholerae serotype O1 or serotype O139 is isolated (in a laboratory) from any suspected case.

After a cholera outbreak has been identified, assume that all cases of acute watery diarrhoea in the area have cholera, with only periodic laboratory testing to confirm that cholera transmission persists and that the outbreak is ongoing.

WHO case definition source of information here.

Cholera can be endemic, epidemic or pandemic.

A cholera outbreak is defined by the occurrence of at least one confirmed case of cholera, with evidence of local transmission in an area where there is not usually cholera.

In endemic areas, an outbreak is defined as a significant increase in the baseline number of cases of cholera (more cases reported than is expected for that period).

• Water contaminated with human faeces, for example from sewage, septic tanks and latrines, is a source of infection. Animal faeces also contain microorganisms that can cause diarrhoea.
• Inadequate access to clean water and sanitation facilities. Water can also be contaminated during transport, storage and handling.
• Food and water when prepared or stored in unhygienic conditions. Raw fruits and vegetables that are contaminated with faeces and not appropriately washed. Seafood taken from contaminated water and eaten raw or not sufficiently cooked.
• Typical at-risk areas include peri-urban slums, and camps for internally displaced persons or refugees, where minimum requirements of clean water and sanitation are not met.
• The consequences of a humanitarian crisis – such as disruption of water and sanitation systems, or the displacement of populations to inadequate and overcrowded camps – can increase the risk of cholera transmission, should the bacteria be present or introduced.
• Oral Rehydration Points (ORPs) or cholera treatment facilities where Infection Prevention and Control (IPC) methods are not appropriately implemented and/or followed.
• Bodies of people who have died from cholera. This includes burial ceremonies where corpses are touched, or food is shared. Uninfected dead bodies have never been reported as the source of epidemics.
• Household members and close neighbours of cholera patients are at increased risk in the days immediately following the person’s illness.

Attack rates will vary from one outbreak to another. In case of an outbreak, consult the latest information provided by health authorities.

According to the Global Task Force on Cholera Control:

• In rural communities with low population density, the AR might vary (0.1–2 per cent)
• In crowded places (such as urban settings, refugee camps), the AR tends to be higher (1–5 per cent).
• In settings with no immunity and poor water and sanitation conditions, AR can exceed 5 per cent.

• Malnourished individuals are more vulnerable to severe cholera diseases, particularly young children. Each cholera and diarrhoeal episode, in turn, makes their malnutrition even worse.
• Individuals with chronic medical conditions (HIV infection, cancer, chronic renal, liver or lung diseases, diabetes, etc.).
• Individuals without ready access to rehydration therapy and medical services.
• Individuals with achlorhydria (the absence of hydrochloric acid in digestive stomach juices), for example because of the use of antacids, histamine receptor blockers and proton pump inhibitors.
• Individuals with blood type O.

Vibrio cholerae bacterium: there are two serogroups – O1 and O139. The clinical and epidemiologic features of both serogroups are very close.

Human host.

Aquatic reservoir.

Faecal oral transmission: Water contaminated with human faeces (from someone who has cholera) is the main mode of transmission. Ingestion of contaminated food and water that have been handled by a person who is shedding Vibrio cholerae through the faeces, or if sewage contaminated with V. cholerae bacteria gets into the water used for drinking or washing food are the main modes of transmission. Contaminated hands, utensils, water or insects can mechanically transfer the organism to food, where the bacteria then multiply to achieve an infective dose. Care should also be taken when handling the bodies of those who have died due to cholera, ensuring strict disinfection and IPC measures. The disease is not likely to spread directly from one person to another by casual contact, and neither is it transmitted through animals.

Two hours to five days.

• Most people infected with Vibrio cholerae do not develop any symptoms, although the bacteria are present in their faeces for one to ten days after infection and are shed (excreted) back into the environment, potentially infecting other people. This is important when considering interventions aimed at stopping transmission via contact tracing alone.

• 20 per cent of infected people develop symptoms and among them 20 per cent develop severe symptoms. Severe disease is characterized by painless profuse watery diarrhoea, often followed by vomiting, leg and abdominal cramps. In these cases, rapid loss of body fluids leads to dehydration and shock. Without treatment, death can occur within hours. Fever is typically absent.

Other infectious diarrhoea, amoebic dysentery, food poisoning.

• When a cholera outbreak is suspected and an alert is triggered, collect stool samples from symptomatic individuals for microbiological confirmation by culture and/or polymerase chain reaction (PCR).
• Cholera rapid diagnostic tests (RDTs) are intended to be used at peripheral healthcare levels only for early outbreak detection and not for individual diagnosis or to confirm the cholera outbreak.
• Once the outbreak is declared, RDTs also permit the triage of specimens to be tested at the laboratory. Samples tested positive by RDT should be prioritized for laboratory testing.
• During a cholera outbreak, assume that all cases of acute watery diarrhoea in the area have cholera and periodic laboratory testing is only needed to confirm that transmission persists, and the outbreak is still ongoing.

Please refer to the appropriate local or international guidelines for clinical management. All clinical management including the administration of any treatment or vaccine should be conducted by health professionals.

Definitive diagnosis is not a prerequisite for the treatment of patients with cholera. The priority in management of any watery diarrhoea is replacing the lost fluid and electrolytes. The case fatality rate in untreated cases may be 30—50 per cent. However, treatment is straightforward and, if provided rapidly and appropriately, the case fatality rate should remain below one per cent.

• In severe dehydration cases hospitalization is required, including the provision of IV rehydration solutions.
• Oral Rehydration Solution (ORS).
• Zinc supplementation – in children under 12 years.
• Antibiotics according to the national protocol.
• The Oral Cholera Vaccine (OCV) has a 50—60 per cent efficacy in preventing episodes of cholera in the first two years after the primary vaccination schedule (Cochrane review). There have been preventive and emergency cholera OCV vaccinations in various countries.

Cholera treatment can be offered at community level through oral rehydration points or at cholera treatment structures such as cholera treatment units, cholera treatment centres or hospitals.

• Previous infection with classical cholera provides protection against subsequent disease lasting between six to ten years.  Previous infection with El Tor Cholera provides protection against subsequent disease lasting three to six years.
• According to the Global Task Force on Cholera Control, two doses of OCV provide protection against cholera for three years. One dose provides short-term protection (at least six months), which has important implications for outbreak management.