Typhoid

Epidemiology, Prevention and Control
of
Typhoid
Compiled notes for MBBS students
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Definition
• Suspected case:
– Fever for at least three out of seven consecutive
days in an endemic area or following travel from
an endemic area*
• Confirmed case:
– Laboratory confirmation by culture or molecular
methods of S.Typhi or detection of S.Typhi DNA
from normally sterile site
– *Countries may opt to use additional criteria to
exclude other diagnoses that are appropriate to
their setting (malaria, dengue etc.)
no.+91 98795 76350

Introduction
• Typhoid fever is caused by bacterium
salmonella subspecies enterica serotype Typhi
– Gram negative bacilli
– Three main Antigens: somatic (O) flagellar (H) ;
freshly isolated strain: capsular (Vi) antigen
– Phage typing/Molecular type is useful in tracing
source of epidemics
• Readily killed by pasteurization
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Introduction
• Mild cases
– no systemic involvement
– Clinical picture of gastroenteritis
– 60-90% cases are mild, receive no attention
• Severe cases
– Altered mental status -Confusion, delirium
– intestinal perforation and death
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Introduction
• Blood culture is diagnostic mainstay for typhoid
– Most frequently isolated during first week of illness
– Can also be isolated during second and third week
• Serological test
– Serological responses to antigens occur by end of first
week
– Widal test measures antibody response to H and O
antigen
– Low sensitivity and specificity – little diagnostic value
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Susceptible Host
Modes of Transmission
Reservoir of infection
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Reservoir of Infection
Humans
• Cases
– Mild cases more common
• Carriers
– On basis of Positive stool culture or PCR
– Temporary(1-2 months) convalescent feacal carrier more
common
– 2-5% become chronic carrier
• Chronic carriers
– Defined as fecal shedding of organism for greater than one
year
– May follow acute illness or mild or subclinical infection
– Common among – middle aged women, billiary tract
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• Source/Infective material:
– Feaces/urine of case/carrier
– Secondary sources are food, water, fingers and flies
• Period of communicability
– As long as bacilli appear in excreta, usually throughout
convalescence*
* Period of infectivity usually few days before onset of
disease to few days after recovery. If it is highly
infectious during incubatory phase or convalescence
phase, it should be remembered. (Silent spreader)
no.+91 98795 76350

Modes of Transmission
Feaco-oral/Urine-oral
Endemic cases:
• Ingestion of contaminated food
Food has large inocula , while water has small (infective dose is high),
salmonella do not multiply in water. Common food items-
– Raw/poorly cooked shell-fish
– Raw fruits and vegetables fertilized by night-soil
– Raw contaminated milk/milk products (alkaline PH)
• contaminated hand
Outbreaks:
• Ingestion of contaminated food/water
• Poorly functioning municipal water supply systemsend suggestion/feedback to whats app
no.+91 98795 76350

Susceptible Host
• Partial/weak immunity follows clinical illness but re-
infection and illness can still occur following large oral
dose
– Being intracellular pathogen cell-mediated immunity plays
major role
– Immunity following natural infection is low among
intracellular bacteria
• Antibody titers not correlated with resistance to re-
infection or relapse
• Increased in individual with gastric achlorhydria
• Children under age five years are at increased risk
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• Social- Environmental factors:
– Open air defecation
– Low standards of food hygiene
– Low standards of personal hygiene
– Contamination of drinking water supplies
So Typhoid may be considered as an index of
general sanitation
• Incubation period: 8-14 days
no.+91 98795 76350

• Prevention:
– Measures applied to prevent occurrence of disease
• Control
– Measures applied to prevent transmission after
disease has occurred
no.+91 98795 76350

Prevention
• Control of Reservoir
– Early diagnosis and treatment ≠
(In acute conditions early diagnosis is not possible)
• Interruption of transmission √ √
– Food
– Water
– Fingers
• Protection of Host
– Immmunoprophylaxis √
(When natural infection confers weak immunity, how
can vaccine ……)
no.+91 98795 76350

Prevention
• To interrupt transmission three essential
measures are:
– Improvement of basic sanitation
– Promotion of food hygiene
– Protection and purification of water supplies
no.+91 98795 76350

Prevention
• Sanitary disposal of human excreta
– Maintain fly-proof latrines
• Food Hygiene
– Raw fruits and vegetables should be peeled
– Boil or pasteurize milk and dairy products
– Cooked food should be eaten hot
– Cleanliness in preparation and handling, storage
– Carriers excluded from food handling
no.+91 98795 76350

Prevention
• Water:
– Protect, purify and chlorinate public water supplies
– Avoid possible contamination with sewer system/backflow
connections
– Boiling or chemical disinfection of water for small group
• Personal hygiene
– After defecation and before preparing, serving or eating
food
– Encourage use of toilet paper to minimize contamination
– Particularly food-handlers and patients & children care
takers
– Provide facilities for hand-washing
no.+91 98795 76350

Prevention
• Fly control measures
– Frequent garbage collection and disposal
– Fly-proof latrines
– Insecticide spraying
– Screening
no.+91 98795 76350

Prevention
• Immunization
– Not routinely recommended in non-endemic area
– Vaccination of high-risk population is considered
most promising strategy
– Two vaccines:
• Oral Ty21a
• Parenteral vaccine
– Booster doses every 2 to 5 years
– Protective (60-70%) against lowt-to-moderate
infecting dose but little protection against large dose
no.+91 98795 76350

Ty21a vaccine:
• Live attenuated vaccine
• Storage 2-8 C (*all vaccines stored at 2-8 C)
• Not licensed for < 5 years
• No antibiotics 3 days before and until 3 days after
• 3 dose - 1,3,5 day, capsules
• Revaccination every 3 years
• C/I – of live vaccines* (immuno-compromised
status, on steroid, pregnancy )
no.+91 98795 76350

Vi polysaccharide vaccine:
• Composed of purified Vi capsular
polysaccharide antigen
• Storage 2-8 C
• Not licensed for children aged < 2 years
• Single human dose 25 ug antigen S.C./I.M.
• Revaccination every three years
• C/I – P/H hypersensitivity reaction
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Prevention
• Control of Reservoir
– Treatment √
– Isolation precautions √
– Tracing source √
• Interruption of transmission √
– Food
– Water
– Fingers
• Protection of Host
– Immmunoprophylaxis √
no.+91 98795 76350

Control
• Treatment of cases:
– F.Q. are drug of choice
– If resistance, select antimicrobial according to sensitivity
pattern
– Ceftriaxone, if oral antibiotics not suitable
• Isolation precautions for cases:
– Enteric precautions
– Until 3 consecutive negative stool cultures at least 24 hrs
apart (48 hrs after antimicrobials)*
– If any positive, repeat at monthly interval
* Period of isolation is determined by period of infectivity.
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• Contacts (Household and close contacts)
– Should not be employed in sensitive occupation until
two negative stool culture
• Tracing source of infection
– Search unreported cases, carriers or contaminated
food, water, milk or shellfish
– Antibody to Vi antigen is often present in high titers in
chronic carriers and can be used as screening test
– Elimination of carrier state achievable with
fluroquinolone therapy; if antibiotics not effective -
cholecystectomy
no.+91 98795 76350

References
• K.Park: Textbook of preventive and social
medicine
• CDC: Control of Communicable Diseases
Manual
• Maxcy: Public health and preventive medicine
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Typhoid

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