CHOLERA

First Published: 2019-04-15 08:42:36 | Last updated: 2019-04-15 07:42:36

Background
Cholera is an acute diarrhoeal disease caused by Vibrio
cholerae; a gram negative rod-shaped 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. There have been seven
pandemics of cholera worldwide, the last of which began
in Indonesia in 1961, with an estimate of between 1.3 to
4.0 million cases and 21,000 to 143,000 deaths globally
due to cholera every year. The World Health Organization
has estimated that officially reported cases represent only
5-10% of actual cases. This “tip `of the iceberg
reporting― is likely due to poor surveillance systems and
inadequate disease notification systems in low and
middle-income countries which are disproportionately
affected by the disease.
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. A
cholera hotspot is a geographically limited area where
environmental, cultural and/or socioeconomic conditions
facilitate the transmission of the disease and where
cholera persists or re-appears regularly. Hotspots play a
central role in the spread of the disease to other regions or
areas.
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. Major epidemics also occurred in 1992, 1995-1996,
and 1997. The Federal Ministry of Health reported 37,289
cases and 1,434 deaths between January and October
2010, while a total of 22,797 cases of cholera with 728
deaths and case-fatality rate of 3.2% were recorded in
2011. Outbreaks were also recorded in 2018 with the
Nigeria Centre for Disease Control (NCDC) reporting
42,466 suspected cases including 830 deaths with a case
fatality rate of 1.95% from 20 out of 36 States from the
beginning of 2018 to October 2018.
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
water, mollusc, fish and aquatic plants are potential
reservoirs.
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. Humanitarian crises and the attendant
displacement of populations to inadequate and
overcrowded camps can increase the risk of cholera
transmission.

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.
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 or people living with HIV – 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.
NCDC also developed additional case definitions in
September 2017 for the community as well as for health
workers as follows:
Community case definition:
Any person 2years and above with lots of watery diarrhea
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 diarrhea 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, for example 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.
Rapid diagnostic tests (RDT) can be used for screening
before confirmation in the laboratory, and there any
several lateral flow devices available, however their low
specificity (and sometimes low sensitivity) can limit their
utility. 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). 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 macrolides,
fluoroquinolones, and tetracyclines depending on
resistance profile.
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 behavioral changes and
improved hygiene practices, as well as quick access to
treatment are essential. Immunisation with Oral Cholera
Vaccine (OCV) can play an important role in outbreak
prevention and control, and in the long-term control of
cholera. The vaccines should always be used in conjunction
with other cholera prevention and control strategies in
areas with endemic cholera, in humanitarian crises with
high risk of cholera, and during cholera outbreaks.
Nigeria References
Adagbada AO, Adesida SA, Nwaokorie FO, Niemogha M,
Coker AO. Cholera Epidemiology in Nigeria: an overview.
Pan African Medical Journal 2012; 12:59
Federal Ministry of Health Nigeria. Weekly Epidemiology
Report. 2011.
Nigeria Centre for Disease Control. Situation Report.
Cholera Outbreak in Nigeria. 29 October 2018
Oyedeji KS, Nwaokorie FO, Bamidele TA, Ochoga M,
Akinsinde KA, Brai BI, et al. Molecular Characterization of
the Circulating Strains of Vibrio cholerae during 2010
Cholera Outbreak in Nigeria. J Heal Popul Nutr. 2013;
31(2):178–84.
World Health Organization. Nigeria. Borno, Adamawa and
Yobe States Declare End of Cholera Outbreaks. 21 January
2019. https://www.afro.who.int/news/borno-adamawa-
and-yobe-states-declare-end-cholera-outbreaks
Further Reading
NCDC:
https://www.ncdc.gov.ng/themes/common/docs/protocols
/45_1507196550.pdf
CDC: https://www.cdc.gov/cholera/index.html
WHO: https://www.who.int/news-room/fact-
sheets/detail/cholera
https://www.afro.who.int/health-topics/cholera