Typhoid and Paratyphoid Fever

Epidemiology of Infectious Diseases: Typhoid and Paratyphoid Fever

Causal agent
A bacterial infection of the intestinal tract and bloodstream.
Salmonella enterica serovar typhi.
Salmonella enterica serovar paratyphi. (types A, B and C).

Common clinical features

  • Symptoms range from mild to severe illness, characterized by the sudden onset of fever, malaise, anorexia, headache, constipation or diarrhoea, rose-coloured spots on the chest area and enlarged spleen and liver.
  • Infection with paratyphoid fever has similar symptoms but is generally a milder disease.


  • Worldwide, particularly in developing countries with poor sanitation, unsafe drinking water and inadequate sewage disposal and flooding.
  • An estimated 16-33 million cases and 500,000 to 600,00 deaths are thought to occur worldwide each year.
  • In endemic areas the highest rates of infection occurs in children aged 5-19 years of age.
  • Most cases reported in developed countries are in travellers to endemic countries.
  • Data from the HPA show a total of 205 cases of S. tyhpi and 212 cases of S. paratyhpi in 2004 reported in England and Wales.


Mode of transmission
Ingestion of food or water contaminated by faeces or urine of patients or carriers.  

Shellfish from sewage-contaminated beds.

Raw fruit, vegetables and contaminated milk have also been implicated in transmission. 

Incubation period
Range 1-3 weeks, commonly 8-14 days, depending on infective dose.
For paratyphoid the range is 1-10 days.

Period of Communicability
While organism is excreted in stool, approximately 10% of patients will be excreting bacilli 3 months after the onset.

The chronic carrier state occurs in approximately 2-5% of infected persons.

Prevention and control
Safe food hygiene practices, especially among overseas travellers.
Immunization is recommended for some overseas travellers and some occupations.


  1. Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
  2. Hawker J, Begg N, Blair I, Reintjes R, Weinberg J. Communicable Disease Control Handbook, Blackwell, 2005.

© CM Kirwan 2006