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Salmonellosis

Epidemiology of Specific Diseases: Salmonellosis

Causal agent
Salmonella enteritidis.
A gram negative bacteria of which more than 2,500 serotypes have been identified.

Salmonella enteritidis and Salmonella typhimurium are the most important serotypes for salmonellosis transmitted from animals to human.

Common clinical features

  • Acute onset of fever, abdominal pain, diarrhoea (sometimes bloody), nausea and vomiting.
  • Effects all age groups. Groups at greatest risk for severe disease and complications include infants, the elderly, the immunocompromised and pregnant women.
  • Complications include septicaemia or localized infection (e.g., septic arthritis) or progress to sepsis.

Epidemiology

  • Endemic worldwide.
  • Salmonellosis is the second most common reported bacterial cause of infectious intestinal disease in the UK.
  • It is estimated that over 60-80% of cases occur sporadically, though large outbreaks are not uncommon1.
  • Multidrug-resistant (MDR) strains of Salmonella have increased considerably in recent years. In recent years there has been an increase in S. typhimurium DT104 and 204b resistant to a number of antibiotics1.  

Reservoir
Domestic and wild animals, including poultry, cattle, swine and domestic and exotic pets.  

Mode of transmission
Salmonella in humans is commonly contracted through the consumption of raw or undercooked food of animal origin (commonly poultry, meat, eggs, contaminated water and milk and milk products).

However, outbreaks have also been traced to the consumption of raw fruit and vegetables contaminated during food preparation. 

Person to person spread via the faeco-oral route may occur, particularly during the diarrhoeal phase of illness.

Contact with infected animals, including exotic pets and domestic animals may also occur. 

Incubation period
6-72 hours, commonly 12-36 hours.

Period of Communicability

  • Throughout the course of infection. The infectious period is highly variable from a few days to a few weeks (median 5 weeks).
  • Approximately 1% of adults and 5% of children will excrete the organism for over 1 year.
  • Immunity is partial.

Prevention and control

  • Follow correct food hygiene practices for food preparation and cooking in domestic and commercial kitchens as described by the WHO Five keys to safer food2.

These include;

  • Prevent cross contamination of raw and cooked food by washing hands before, during and after food preparation.  Wash and sanitize all equipment, surfaces and utensils used for food preparation.
  • Separate raw and cooked food, and use separate equipment and utensils for handling raw food.
  • Cook food thoroughly (until centre of food reaches at least 70oC), especially poultry, meat, eggs and seafood.
  • Reheat cooked food thoroughly, and store cooked and raw food at a safe temperature.
  • Use safe water and raw materials, e.g. pasteurized milk and water.
  • Wash fruit and vegetables.
  • In the UK Salmonellosis infection is notifiable as 'suspected food poisoning'.

 References

  1. Hawker J, Begg N, Blair I, Reintjes R, Weinberg J. Communicable Disease Control Handbook, Blackwell, 2005.
     
  2. World Health Organization: 5 Keys to Safer Food. Available at http://www.who.int/foodsafety/publications/consumer/5keys/en/

Further Resources

HPA. Salmonella Enteritidis non -Phage Type 4 Infections in England and Wales: 2000-2004 - report from a multi-Agency national outbreak control team. Commun Dis Rep CDR Wkly[serial online] 2004 [cited 14 October];14 (42):News. Available at
http://www.hpa.org.uk/cdr/PDFfiles/2004/cdr4204.pdf

WHO, Fact sheet No139, April 2005. Available at http://www.who.int/mediacentre/factsheets/fs139/en/

© CM Kirwan 2006