Epidemiology of cholera

EPIDEMIOLOGY OF
CHOLERA
Namita Batra Guin
Associate Professor
Dept. of Community Health Nursing

INTRODUCTION
• Is an acute diarrhoeal disease caused by Vibrio
Cholerae.
• Cases range from symptomless to severe infections
• Typical cases are characterized by the sudden onset of
profuse, effortless, watery diarrhoea followed by
vomiting, rapid dehydration, muscular cramps and
suppression of urine.
• Unless there is rapid replacement of fluid and

INTRODUCTION
• Cholera transmission is closely linked to
inadequate environmental management.
• Typical at risk areas include peri urban
slums with poor basic infrastructure.

AGENT FACTORS
• The agent that causes cholera is named as Vibrio
cholerae.
• Vibrio cholerae are killed within 30 min by heating
at 56 deg C, or with in 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 (6 mg/lit) instantly kills the
organism.

AGENT FACTORS
• The vibrios multiply in the small intestinal
lumen and produce an exotoxin
(enterotoxin).
• This toxin produces diarrhoea through
its effect on the adenylate cyclase-cyclic
AMP system of the mucosal cells of the
small intestine
• The endotoxin has no effect on other
tissues except the intestinal epithelial

RESERVOIR OF INFECTION
• The human being is the only known reservoir
• The individual may be a case or a carrier
• Cases range from inapparent infections to severe
ones
• Individuals with low immunity (undernourished
children, people with HIV) are at a greater risk of death
if infected.
• It is the mild and asymptomatic cases that play a
significant role in maintaining endemic reservoir

RESERVOIR OF INFECTION
• Since carriers excrete fewer vibrios than clinical
cases, carriers best detected by bacteriological
examination of the purged stool induced by
administration of 30-60 g of magnesium sulphate
in 100 ml of water by mouth.

Infective Material
• The immediate source of infection are the stools
and vomit of cases and carriers
• Large number of vibrios (107-1010 vibrios /ml of
fluid) are present in watery stools of patients
• An average patient excretes 10- 20 litres of fluid
• Carriers excrete fewer vibrios than cases (102-
105 vibrios / ml stool)

INFECTIVE MATERIAL
• The immediate source of infection are the stools
and vomit of cases and carriers
• Large number of vibrios (107-1010 vibrios /ml of
fluid) are present in watery stools of patients
• An average patient excretes 10- 20 litres of fluid
• Carriers excrete fewer vibrios than cases (102-
105 vibrios / ml stool)

PERIOD OF COMMUNICABILITY
◦ A case of cholera is infectious for a period of 7-10 days
◦ Convalescent carriers are infectious for 2-3 weeks and
chronic carrier state may last from a month upto 10
years or more

CARRIERS
◦ Four types of cholera carriers have been identified
◦ PRECLINICAL or INCUBATORY CARRIERS: The incubatory carriers are potential
patients (since the incubation period of cholera is short ;1-5 days, incubatory carriage
is of short duration)
◦ CONVALESCENT CARRIERS: Patients who have recovered from an attack of
cholera may continue to excrete vibrios during the convalescence period for 2-3
weeks
◦ CONTACT or HEALTH CARRIERS: This is the result f sub clinical infection contracted
through association with a source f infection (in case of an infected environment). The
duration of contact carrier state is usually less than 10 days.
◦ CHRONIC CARRIERS: A chronic carrier state occurs infrequently. The gall bladder is
infected in this state. In such case antibody titre against V. cholerae 01 raises and
remains positive as long as the person harbours the organism

HOST FACTORS
• AGE & GENDER: Cholera affects all age and both gender. In
endemic areas attack rate is highest in children
• GASTRIC ACIDITY : Is an effective barrier. The vibrio is destroyed
at an acidity of pH 5 or lower. Condition that affect gastric acidity
may influence individual susceptibility.
• POPULATION MOBILITY: Movement of population (pilgrimage,
marriages, fairs & festivals) results in increased risk of exposure to
infection
• ECONOMIC STATUS: Incidence of cholera tends to be highest in
the lower socio economic groups which could be attributed to poor
hygiene
• IMMUNITY: An attack of cholera is followed by immunity to re
infection, but the duration and degree of immunity are not known.
Vaccination gives only partial immunitybfor3-6 months.

ENVIRONMENTAL FACTORS
• Vibrio transmission is highly possible in a community
with poor environmental sanitation.
• The environmental factors of importance include
contaminated water and food
• These comprise certain human habits favouring water
and soil pollution, low standards of personal hygeine,
lack of education and poor quality of life

MODES OF TRANSMISSION
◦ Transmission occurs from man to man via fecally contaminated water,
contaminated food and drinks and by direct contact
◦ FAECALLY CONTAMINATED WATER: Uncontrolled water sources such as
wells, ponds, lakes, streams and rivers pose a great threat.
◦ CONTAMINATED FOOD AND DRINKS: Ingestion of contaminated food
and drinks have been associated with the outbreak of cholera. Bottle
feeding could be a significant risk factor for infant.
◦ DIRECT CONTACT: In developing countries considerable number of cases
may result from secondary transmission (person to person transmission
through contaminated fingers while carelessly handling human excreta or
vomitus of patients & through contaminated linens and fomites.

INCUBATION PERIOD
◦ Incubation period ranges from a few hours upto 5 days,
commonly 1-2 days

PATHOGENESIS
• Diarrhoea is the main symptom of cholera
• The pathogen gets through the mucus which overrides the intestinal
epithelium
• This probably secretes mucinase which helps the organism to move
rapidly through the mucus
• Then the vibrio gets attached or adhered to the intestinal epithelial
cells.
• When the vibrio becomes adherent to the mucosa, it produces its
enterotoxin which consists of 2 parts (the light or L toxin and heavy
or H toxin)

PATHOGENESIS
• The L toxin combines with substances in the epithelial cell
membrane called gangliosides and this binds the vibrios to the
cell wall. Binding is irreversible.
• The mode of H toxin is not fully clear. However the H toxin
activates the adenyl cyclase in the intestinal epithelial cells.
The activated adenyl cyclase causes a rise in in 3,5 adeosine
monophosphate (cAMP)
• The cAMP provides energy which drives the fluid and ions
into the lumen of intestine.
• This fluid is isotonic and is secreted by all segments of small
intestine. The increase in fluid is the cause of diarrhoea (and
not peristalsis)

CLINICAL FEATURES
• The severity of cholera depends on the rapidity and
duration of fluid loss.
• A typical case of cholera shows three stages:
1. Stage of evacuation
2. Stage of collapse
3. Stage of recovery

◦ 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 rice watery appearance
◦ STAGE OF COLLAPSE: The patient then passes into the stage of collapse
because of dehydration.
◦ The classical signs are sunken eyes, hollow cheeks, scaphoid abdomen, sub
normal temperature, washer man’s hands and feet, absent pulse, unrecordable
blood pressure, loss of skin elasticity, shallow and quick respirations. The output of
urine decreases and may ultimately cease.
◦ The patient becomes restless and complains of intense thirst and cramps in legs
and abdomen. Death may occur at this stage, due to dehydration and acidosis
resulting from diarrhoea.
◦ STAGE OF RECOVERY: If death does not occur then patients begin to show signs
clinical improvement. The blood pressure begins to raise, the temperature returns to
normal and urine secretion is re established. If anuria persists, the patient may die
of renal failure

LAB DIAGNOSIS
• COLLECTION OF STOOLS: a fresh specimen of stools should be collected for
laboratory examination. Sample should be collected before the person is treated
with antibiotics. Collection may be made in one of the following ways.
• RUBBER CATHETHER COLLECTION: Soft rubber catheter (No.26-28) sterilized
by boiling should be used. The catheter is introduced (after lubrication with liquid
paraffin) for atleast 4-5 cm into the rectum. The specimen voided may be collected
directly into a transport media (VR medium, alkaline peptone water)
• RECTAL SWAB: Swabs consisting of 15-20 cm long wooden sticks with one end
wrapped with absorbant cotton, sterilized by autoclaving can be also used Rectal
swabs should be dipped with into the holding medium before being introduced into
the rectum.
• If no transport medium is available, a cotton tipped rectal swab should be
soaked in the liquid stool, placed in a sterile plastic bag, tightly sealed and
sent to testing laboratory

LAB DIAGNOSIS
• VOMITUS: This is practically never used as the chances of isolating vibrios
are much less and there is no advantage
• WATER: Samples containing 1-3 litres of suspect water should be collected
in sterile bottles (for filter method) Or 9 volumes of sample water added to 1
volume of 10 per cent peptone water and despatched to the lab by quickest
method of transport
• FOOD SAMPLE : Samples of food suspected to be contaminated with
vibrios amounting to 1-3 gms are collected in a transport media and sent to
lab
• TRANSPORTATION: the stool should be transported in sterilized
McCartney bottles 30 ml capacity containing alkaline peptone water or VR
medium

• One gram or one ml of faeces in 10 ml of the holding
medium will suffice
• Rectal swabs should have their tops broken off hat caps
of the containers can be replaced.
• DIRECT EXAMINATION: If a microscope with dark field
illumination is available it may be possible to diagnose about
80 percent of cases within few min
• CULTURE METHODS: On arrival at the laboratory the
specimen is well shaken abd about 0.5 to 1 ml material is
inoculated into Peptone Water Tellurite medium for
enrichment.
• GRAM TESTING: Gram negative and curved rods with
characteristic scintillating type of movement in hanging drop
preparations are characteristic of Vibrio cholerae.

◦ The following are guidelines as per WHO to control cholera
• 1. Verification of the diagnosis
• 2. Notification
• 3. Early case finding
• 4. Establishment of treatment centres
• 5. Rehydration therapy
• 6.Adjuncts to therapy
• 7. Epidemiological investigation
• 8. Sanitation measures
• 9. Chemoprophylaxis
• 10. Vaccination
• 11. Health education

◦ Verification & diagnosis: It is important to confirm the outbreak of
cholera . All cases of diarrhoea should be investigated even on
slightest suspicion.
◦ Notification: Cholera is a notifiable disease locally and nationally
(though not internationally). Health workers at all level should be
trained to identify and notify cases immediately to the local health
authority
◦ Early case Finding: An aggressive search for case (mild, moderate,
severe should be made in the community to be able to initiate prompt
treatment. Early detection of cases also permits the detection of
infected household contacts and helps the epidemiologist in
investigating the means of spread for deciding on specific
intervention.
◦ Establishment of treatment centers: In control of cholera no time
should be lost in for providing treatment to patients. Hence treatment

◦ Rehydration therapy: Mortality rated due to cholera can be
effectively brought down by effective rehydration therapy.
Rehydration may be oral or intravenous
◦ Adjuncts to Therapy: Antibiotics should be given as soon as
vomiting stops. The commonly used antibiotics are
flouroquinolones, tetracycline, azithromycin, ampicilline and
trimethioprim slfamethoxazole.
◦ Epidemiological Investigation: Epidemiological studies may be
undertaken to define the extent of outbreak, and identify the
modes of transmission so as to identify specific control measures.
◦ Sanitation Measures: Sanitation measures focusing on water
sanitation, excreta disposal, food sanitation, disinfection should
be put into vigorous interventions.

◦ Chemoprophylaxis: Mass chemoprophylaxis is not advised for
the entire community. Chemoprophylaxis is advised for house
hold contacts.
◦ Tetracycline is the drug of choice for mass chemoprophylaxis. It
has to be given over a 3 day period, in twice daily dose of 500
mg for adults, 125 mg for children aged 4-13 yrs and 50 mg for
children aged 0-3 years.
◦ Vaccination: Two types of vaccination are available :
◦ 1. Dukoral (WC-rBS) – Monovalent, heat killed vaccine. Not
advised for children less than 2 years of age.
◦ 2. Sanchol & mORCVAX- Oral vaccine. Bivalent.
◦ Health Education: The benefit of early reporting and proper
hygiene measures should be taught to the community

Epidemiology of cholera

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