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paratyphoid

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Typhoid and paratyphoid fevers are collectively known as enteric fevers and they are caused respectively by the organisms Salmonella typhi and Salmonella paratyphi (types A, B and C). Both of these organisms are primarily human pathogens, though S. paratyphi type B has been known to infect cattle.

  • transmission is primarily via the oral route following ingestion of food or water contaminated by faeces and occasionally the urine of persons acutely ill with typhoid or those who are chronic carriers
    • direct faecal-oral transmission can also occur
    • in healthy individuals, one million or more organisms may be required to cause illness, however, ingestion of fewer organisms may still result in illness, especially in susceptible individuals
    • incubation period varies from one to three weeks, depending on host factors and the size of the infecting dose
    • risk of contracting typhoid fever is highest for travellers to areas of high endemicity. In the Indian subcontinent, a region of high incidence of typhoid fever (more than 100 cases per 100,000 people per year, the attack rate for travellers has been estimated at 1 to 10 per 100,000 journeys
  • following ingestion of contaminated food or water, S. typhi penetrates the intestinal mucosa, replicates and enters the bloodstream
    • severity of symptoms varies. Clinical features range from mild fever, diarrhoea, myalgia and headache to severe disseminated disease with multi-organ involvement in 10–15% of cases
  • case fatality rate (CFR) is less than 1% with prompt antibiotic therapy, but may be as high as 20% in untreated cases.
  • typhoid has previously been thought to be a milder disease in children
    • more recent datat, however, indicates that typhoid can cause significant morbidity in children aged one to five years who reside in endemic countries

Enteric fevers are systemic, bacteraemic illnesses which should not be confused with food poisoning or Salmonellosis. The latter are caused by different species of Salmonella, and unlike enteric fevers they often present with acute diarrhoea.

Both typhoid and paratyphoid are notifiable diseases.

Reference:

  1. Immunisation Against Infectious Disease - "The Green Book".Chapter 33 Typhoid (August 2006).
  2. Int J Epidemiol (1985) 14:169-72
  3. BMJ (1990) 300:1687-90

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