Epidemiology

of

Typhoid fever

• Typhos in Greek means ,smoke and typhus fever got its name from smoke that was believed to cause it. Typhoid means typhus-like and thus the name given to this disease.

• The term Typhoid was given by Louis 1829 to distinguish it from typhus fever.

• It is a disease of poor environmental sanitation and hence occurs in parts of the world where water supply is unsafe and sanitation is substandard.

• In 1880s, the typhoid bacillus was first discovered by Eberth in spleen sections and mesenteric lymph nodes from a patient who died from typhoid.

• Robert Koch confirmed a related finding and succeeded in cultivating the bacterium in 1881.

• Serodiagnosis of typhoid was thus made possible by 1896.

• Wright and his team prepared heat killed vaccine from S.Typhi in 1896

• Disease caused by Salmonellae typhi. Non-spore-forming. gram – ve rods, aerobic, motile

with flagella,

• Salmonella currently comprise 2000 serotypes Two groups a) Enteric fever group b) Food poisoning group

• The proportion of typhoid to paratyphoid A is 10:1.

• The bacilli are killed at 55ºc in one hour or at 60ºc in 15 minutes.

• They are killed within 5 minutes by mercuric chloride or 5% phenol.

• Boiling or chlorination of water and pasteurization of milk destroy the bacilli

Salmonella enterica.

• In past, many deaths were due to typhoid fever worldwide.

Now mostly

• localized to developing countries.• People are not only become ill and die but can

become colonized by S. typhi resulting in being carriers and spread typhoid fever.

• An acute infection with prolonged fever due to Salmonella typhi sometimes lead to severe complications.

• Globally 16 million cases with 600000 deaths annually.

• Salmonella paratyphi A & B lead to milder disease.

• Peak age 4-19 years.

Typhoid Fever

Ingest S. typhi

Bacteria invades intestinal cells and translocates to systemic organs

Multiplies to high number in liver and spleen

Spreads to bloodstreamBacteria move to gallbladder

Shed in Bile

DEATH

Bacteria persistsin gallbladder

Bacteria shed infeces

TYPHOID

Poorer Countries are Vulnerable

• Typhoid Fever seems to matriculate in places with poor sanitary conditions.

• Places where water is not sanitized provides the perfect environment for Typhoid Fever.

• Age group : Typhoid fever may occur at any age but it is considered to be a disease mainly of children and young adults. In endemic areas, the highest attack rate occurs in children aged 8-13 years. In a recent study from slums of Delhi, it was found that contrary to popular belief, the disease affects even children aged 1-5 years

Gender and race : Typhoid fever cases are more commonly seen in males than in females. On the contrary, females have a special predilection to become chronic carriers.

Occupation : Certain categories of persons handling the infective material and live cultures of S. typhi are at increased risk of acquiring infection.

Socio-economic factors : It is a disease of poverty as it is often associated with inadequate sanitation facilities and unsafe water supplies.

• Environmental factors : Though the cases are observed through out the year, the peak incidence of typhoid fever is reported during summer. This period coincides with July - September rainy season and a substantial increase in fly population.

• Social factors : pollution of drinking water supplies, open air defecation, and urination, low standards of food and personal hygiene, and health ignorance.

Nutritional status :Malnutrition may enhance the susceptibility to typhoid fever by altering the intestinal flora or. other host defences.

Incubation period : Usually 10-14 days but it may be as short as 3 days or as long as 21 days depending upon the dose of the inoculums.

Reservoir of infection : Man is the only known reservoir of infection - cases or carriers

Period of communicability: A case is infectious as long as the bacilli appear in stool or urine.

Risky groups

• Children and young adults in endemic areas.

• Contacts of chronic carriers.

• Microbiology technicians.

• Food handlers.

• Travelers and military personnel

Typhoid carriers• About 1–5% of people who are infected with

S. typhi become asymptomatic chronic carriers.

• The carrier state may follow acute or mild illness or subclinical infection.

• The incidence of chronic carriage is higher among women and persons with biliary tract abnormalities.

•

• Antibiotic use and antibiotic resistance may also affect the propensity to become a chronic carrier.

• A chronic urinary carrier state occurs in individuals with schistosome infection.

• Carriers who handle food without observing proper hygiene can transmit infection to others.

Transmission

• Typhoid is spread by the faecal-oral route. Occasionally transmission may be direct, but usually it occurs following the ingestion of contaminated water or food.

• In developing countries with contaminated water supplies and primitive sewage disposal systems, water is the most likely vehicle of transmission.

Epidemics originating from water contamination are particularly explosive.

Because: • a water source may serve a large population.

• Water dilutes gastric acid which would otherwise inactivate pathogenic agents.

• Water and other beverages remain in the stomach only very briefly.

• In more developed countries, with good sanitation, typhoid transmission is more likely to be associated with food contamination..

To summarize:

Modes of transmission:

• Water contaminated with fecal materials.

• Contaminated food.

• Food handlers.

Reservoir:

Only human (cases & carriers)

Communicability

• Typhoid is communicable as long as S. typhi organisms are excreted, usually from the first week and throughout convalescence.

• About 10% of untreated typhoid fever patients will excrete bacteria for 3 month after onset of symptoms.

Carriers may be temporary or chronic.• Temporary (convalescent or

incubatory) carriers usually excrete bacilli up to 6-8 weeks.

• Chronic carriers : By the end of one year, 3-4 per cent of cases continue to excrete typhoid bacilli.

Prevention and control

• Basic sanitary and hygienic measures

Purifying water supplies.

Improving water delivery and sewage control.

Construction and use of latrines.

Boiling water

Supervision of foodhanders.

Vaccines

• Three vaccines to typhoid fever:

1. Killed whole bacteria with side effects.

2. Capsular material (Vi antigen) that is safer and more effective.

3. Live oral vaccine, attenuated S. typhi strain (Ty21a). Oral vaccines are still being developed to distribute in

developing countries. Ty21a is also being used to carry foreign antigens from Shigella and V. cholerae.

Vaccine Name

How given

Number of doses necessar

y

Time between doses

Total time

needed to set

aside for vaccinati

on

Minimum age

for vaccinati

on

Booster needed every...

Ty21a (Vivotif Berna, Swiss Serum and Vaccine Institute) ------------

1 capsule

by mouth

4 2 days 2 weeks 6 years 5 years

ViCPS (Typhim

Vi, Pasteur Merieux)

Injection 1 N/A 2 weeks 2 years 2 years

• Indication of vaccination:

Travellers to endemic areas.

People in refugee camps.

Microbiologists.

• Treatment:

Antibiotics : Ciprofloxacin, pefloxacin & cephalosporins

If you know you are traveling to an at risk location:

• Avoid Ice

• Drink Only Bottled Water

• Make sure all food is thoughoughly cooked.

INTERNET REFERENCESwww.worldwidevaccines.com

www.health.gov

www.rush.edu/worldbook/medical

www.cdc.gov

www.nlm.nih.gov

www.who.int