Epidemiology of Cholera

Cholera
Dr. Shubhangi S. Kshirsagar
Assistant professor
Department of Swasthavritta & Yoga
drssksagar@gmail.com

Cholera is an acute diarrhoeal disease caused by
V. Cholerae O1 (classical or El Tor} and O139.
It is now commonly due to the El Tor biotype and
O139.
Cases range from symptomless to severe infections.
The majority of infections are mild or asymptomatic.
Typical cases are characterized by the sudden onset of
profuse, effortless, watery diarrhoea followed by
vomiting, rapid dehydration, muscular cramps and
suppression of urine.
Cholera
2
Dr. Shubhangi Kshirsagar

Epidemiological
determinant
3

1. Agent factors
a. Agent - V. cholerae O Group 1 or Vibrio cholerae O1
and O139.
b. Resistance -
V. cholerae are killed within 30 minutes by heating at 56
deg.C or within a few seconds by boiling.
They remain in ice for 4-6 weeks or longer.
Drying and sunshine will kill them in a few hours.
They are easily destroyed by coal tar disinfectants such
as cresol.
Bleaching powder is another good disinfectant which
kills vibrios instantly at 6 mg/litre. 4

c. Toxin production
The vibrios multiply in the lumen of the small intestine
and produce an exotoxin (enterotoxin).
This toxin produces diarrhoea through its effect on the
adenylate cyclase-cyclic AMP system of mucosal cells
of the small intestine.
5

d. Reservoir of infection – only human - case or carrier.
i. Cases –
Cases range from inapparent infections to severe ones.
About 75 % of people infected with V. cholerae do not
develop any symptoms, although the bacteria are present
in their faeces for 7-14 days after infection and are shed
back into the environment, potentially infecting other
people.
Among people who develop symptoms, about 20 %
develop acute watery diarrhoea with severe dehydration.
ii. Carriers - usually temporary, rarely chronic.
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e. Infective material
Stools and vomit of cases and carriers.
Large numbers of vibrios (about 107-109 vibrios per ml of
fluid) are present in the watery stools of cholera patients.
Average patient excretes 10-20 litres of fluid.
Carriers excrete fewer vibrios than cases, 102-105 vibrios per
gram of stools.
f. Infective dose
Infection occurs when the number of vibrios ingested
exceeds the dose that is infective for the individual.
In the normal person a very high dose-something like 1011
organisms - is required to produce the clinical disease. 7

g. Period of communicability
A case of cholera is infectious for a period of 7-10 days.
Convalescent carriers are infectious for
2-3 weeks.
The chronic carrier state may last from a month
up to 10 years or more.
8

Host factors
a. Age & sex - affects all ages and both sexes.
In endemic areas, attack rate is highest in children.
b. Gastric acidity - The vibrio is destroyed in an acidity
of pH 5 or lower.
c. Population mobility – Movement of population (e.g.
pilgrimages, marriages, fairs and festivals) results in
increased risk of exposure to infection.
d. Economic status - highest in the lower socio-
economic groups
e. Immunity - Vaccination gives temporary , partial
immunity for 3-6 months. 9

Environmental factors
1. Poor environmental sanitation
2. Contaminated water & food
3. Flies may carry vibrio, but not vector
4. Social factors
Low standard personal hygiene
Lack of education
Poor quality of life
Human habits –favoring water and soil pollution
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Mode of transmission
1. Faecally contaminated water
2. Contaminated food & drinks
Bottle feeding - significant risk factor for infant
Foods and vegetables washed with contaminated water can
be a source of infection
After preparation, cooked food may be contaminated through
contaminated hands & flies.
3. Direct contact
Person to person transmission through contaminated fingers
while carelessly handling excreta & vomit of patient and
contaminated linens & fomites. 11

Incubation period
Few hours to 5 days
But commonly 1-2 days
12

Clinical features
1. Stage of Evacuation
2. Stage of Collapse
3. Stage of Recovery
Typical case of cholera consist of following stages -
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Clinical features
1. Stage of evacuation
The onset is abrupt with profuse, painless, watery
diarrhoea followed by vomiting.
The patient may pass as many as 40 stools in a day.
The stools may have a “rice water” appearance.
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2. Stage of collapse
The patient soon passes into a stage of collapse because of
dehydration.
The classical signs are –
Sunken eyes
Hollow cheeks
Scaphoid abdomen
Sub-normal temperature, pulse absent
Washerman's hands and feet
Unrecordable blood pressure
Loss of skin elasticity
Shallow and quick respirations
Output of urine decreases and may ultimately cease
Patient becomes restless, complains of intense thirst and
cramps in legs and abdomen.
Death may occur at this stage, due to dehydration and
acidosis resulting from diarrhoea.
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3. Stage of recovery
If death does not occur, the patient begins to show signs
of clinical improvement.
The blood pressure begins to rise, the temperature returns
to normal, and urine secretion is re-established.
If anuria persists, the patient may die of renal failure.
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Laboratory diagnosis
1. Collection of stools
Fresh specimen of stool should be collected
Collection before the person is treated with antibiotics.
Specimen is collected in following ways –
a. Rubber catheter method
b. Rectal swab
2. Vomitus
3. Water – suspect water collection
4. Suspected food samples 1-3gm (contaminated with V.
Cholarae)
5. Transportation - stool should be transported
in sterilized McCartney bottles, 30 ml capacity containing
alkaline peptone water or VR medium.
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6. Direct examination – in the dark field, the vibrios evoke
the image of many shooting stars in a dark sky.
7. Culture method
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Control of Cholera
"Guidelines for Cholera Control" proposed by the WHO
are -
1. Verification of the diagnosis
2. Notification
3. Early case finding
4. Establishment of treatment centers
5. Rehydration therapy
6. Adjuncts to therapy
7. Epidemiological investigations
8. Sanitation measures
9. Chemoprophylaxis
10. Vaccination 19

Control of Cholera
1. Verification of the diagnosis
It is important for confirmation of the outbreak as
quickly as possible.
All cases of diarrhoea should be investigated
For the specific diagnosis of cholera, it is
important to identify V. cholerae 01 in the stools of
the patient.
Once the presence of cholera has been proved, it is
not necessary to culture stools of all cases or
contacts.
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2. Notification
Cholera is a notifiable disease locally and nationally.
Since 2005 cholera notification is no ·longer mandatory
internationally.
Under the International Health Regulations,
cholera is notifiable to the WHO within 24 hours of its
occurrence by the National Government.
The number of cases and deaths are also to be reported
daily and weekly till the area is declared free of cholera.
An area is declared free of cholera when twice the
incubation period (i.e., 10 days) has elapsed since the death,
recovery or isolation of the last case.
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3. Early case-finding
An aggressive search for cases (mild, moderate,
severe) should be made in the community to be able
to initiate prompt treatment.
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4. Establishment of treatment centres
The mildly dehydrated patients should be treated at home with
oral rehydration fluid.
Severely dehydrated patients, requiring
intravenous fluids, should be transferred to the nearest
treatment centre or hospital.
If possible, they should receive oral rehydration on the way to
the hospital or treatment centre.
If there is no hospital or treatment centre within a
convenient distance, a local school or public building should be
taken over and converted into a temporary treatment centre.
In areas where peripheral health services are poor and
cholera is endemic or threatening, mobile teams should be
established at the district level 23

5. Rehydration therapy - may be oral or intravenous.
6. Adjuncts to therapy
Antibiotics should be given as soon as vomiting has
stopped, which is usually after 3 to 4 hours of oral
rehydration.
Injectable antibiotics, have no special advantages.
The commonly used antibiotics for the treatment of
cholera are flouroquinolones, tetracycline,
Azithromycin, ampicilline and Trimethoprim TMP
Sulfamethoxazole (SMX).
No other medication should be given to treat cholera,
like antidiarrhoeals, antiemetics.
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7. Epidemiological investigations
At the same time, epidemiological studies must be
undertaken to define the extent of the outbreak and
identify the modes of transmission, so that more effective
and specific control measures can be applied.
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8. Sanitation measures
a. Water control
Provision of piped water supply
In rural areas, water can be made safe by boiling or by
chlorination
b. Excreta disposal
Provision of sanitary latrines
Importance of hand washing with soap after
defecation
c. Food sanitation
d. Disinfection 26

9. Chemoprophylaxis
Studies have shown that approximately 10-12 per cent of
close household contacts of a cholera case may be
bacteriologically positive, and some of these develop
clinical illness.
In contrast, a very small proportion (0.6-1 per cent)
in the community may be excreting vibrios.
Mass chemoprophylaxis is not advised for the total
community.
Tetracycline is the drug of choice for chemoprophylaxis.
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10. Vaccination
1. Dukoral (WC-rBS)
2. Sanchol and mORCVAX
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11. Health education
It should be directed mainly to -
Effectiveness and simplicity of oral rehydration
therapy
Benefits of early reporting for prompt treatment
Food hygiene practices
Hand washing after defecation and before eating
Benefit of cooked, hot foods and safe water
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Epidemiology of Cholera

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Epidemiology of Cholera