Background
Cholera is an acute diarrhoeal disease caused by Vibrio cholerae; a Gram negative curved bacterium. It is a potentially life-threatening, primarily waterborne disease. There are many serogroups of V. cholerae, but only two (O1 and O139) cause outbreaks.
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Cholera can be both endemic and epidemic. A cholera-endemic area is an area where confirmed cholera cases were detected during 3 out of the last 5 years with evidence of local transmission.
A cholera outbreak/epidemic can occur in both endemic countries and in countries where cholera does not regularly occur.
In Nigeria, cholera is an endemic and seasonal disease, occurring annually mostly during the rainy season and more often in areas with poor sanitation, with the first series of cholera outbreaks reported between 1970 and 1990.
Cholera is an epidemic prone disease for immediate notification on the Integrated Disease Surveillance and Response (IDSR) platform in Nigeria.
Transmission
Humans are the main reservoir of Vibrio cholerae but contaminated water, food, mollusc, fish and aquatic plants are potential reservoirs.
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The bacteria are transmitted mainly through the faeco-oral route via ingestion of contaminated food or water. Cholera transmission is closely linked to inadequate access to clean water and sanitation facilities. Typical at-risk areas include peri-urban slums, where basic infrastructure is not available, as well as camps for internally displaced persons or refugees.
Symptoms
Cholera has an incubation period of between two hours and five days, and is asymptomatic or mild in 80% of cases, with only about one in 10 infected people developing the typical signs and symptoms of cholera disease, usually within a few days of infection. Cholera is characterised by rapid onset of profuse watery diarrhoea (rice water stools), with or without vomiting. It is usually not associated with fever and is highly contagious. Severe cases can lead to death within hours due to dehydration.
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Case fatality ratios can be up to 50%, especially in people without access to treatment but this drops to 1% with adequate treatment. People with low immunity such as malnourished children are at a greater risk of death if infected.
The Technical Guidelines for IDSR in Nigeria gives the following standard case definitions:
Suspected case:
In a patient aged 5 years or more, severe dehydration or death from acute watery diarrhea.
If there is a cholera epidemic, a suspected case is any person age 5 years or more
with acute watery diarrhoea, with or without vomiting.
Confirmed case:
A suspected case in which Vibrio cholerae O1 or O139 has been isolated in the stool.
Community case definition:
Any person 2 years and above with lots of watery diarrhoea
Suspected case:
Any patient aged 2 years presenting with acute watery diarrhoea and severe dehydration or dying from acute watery diarrhoea with or without vomiting.
In areas where a cholera outbreak is declared, any person presenting with or dying from acute watery diarrhoea with or without vomiting.
Diagnosis/Testing
Stool samples should be collected once the patient presents and before antibiotics have been administered.
The gold standard is culture of V. cholerae on selective media such as thiosulfate citrate bile sucrose (TCBS) agar, with serogrouping and serotyping by antibody agglutination to confirm an outbreak strain. This also allows for antimicrobial susceptibility testing and advice on appropriate antibiotic administration.
Stool samples can be enriched in alkaline peptone water to help with recovery, and field samples can be sent in Cary-Blair transport media.
Darkfield microscopy of fresh rice-water stools can also be used to identify the motile V. cholerae bacteria.
Treatment
The majority of affected people can be treated successfully through prompt administration of oral rehydration solution (ORS).
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Severely dehydrated patients are at risk of shock and require the rapid administration of intravenous fluids.
Such patients should also be given appropriate antibiotics to diminish the duration of diarrhoea, reduce the volume of rehydration fluids needed, and shorten the amount and duration of V. cholerae excretion in their stool.
Rapid access to treatment is essential during a cholera outbreak.
Antibiotics may also shorten the duration and severity of symptoms and are a useful adjunctive therapy, the choice includes Azithromycin, Ciprofloxacin and Doxycycline.
Infection Prevention and Control (IPC)
Good personal hygiene should be emphasised, as well as proper disposal of sewage and refuse, good hand washing practices and consumption of safe water and food.
Enhanced epidemiological and laboratory surveillance to identify endemic areas and detect, confirm, and quickly respond to outbreaks help in control of infection.
Community engagement for behavioural changes and improved hygiene practices, as well as quick access to treatment are essential.