salmonella food poisoning excluding enteric fevers

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Salmonellosis excluding enteric fever/ Salmonella species excluding S. Typhi and S. Paratyphi

Salmonella is an important cause of food poisoning, and after campylobacteriosis it is the second most common cause of bacterial diarrhoea in the UK.

There are many types of non-typhoid salmonella, most of which inhabit animal intestines. However, a few commonly infect man, including S. enteritidis, S. typhimurium, S. virchow, S. hadar, S. heidelberg, S. agona and S. indiana. The prevalence of each serotype changes regularly in different areas.

Infection usually occurs via contaminated meat and eggs, and the clinical effects are varied, either presenting as an acute enterocolitis or invasive salmonellosis.

Salmonellosis should not be confused with enteric fevers which are systemic, bacteraemic illnesses caused by S. typhi and S. paratyphi and present in a more non-specific manner.

Summary:

Reservoir:

  • gastrointestinal tract of wild and domestic animals, birds (especially poultry), reptiles, amphibians (for example, terrapins), and occasionally humans

Epidemiology:

  • there are >2500 serotypes of Salmonella
  • Salmonella Enterica serovar, S. Enteritidis and S. Typhimurium are the most commonly identified in the UK, Europe and USA
  • Cases often appear sporadic, but outbreaks occur in the general population and institutions

Transmission:

  • predominantly through consuming foodstuffs (most often red and white meats, raw eggs, milk, and dairy products) following contamination of cooked food by raw food or failing to reach adequate cooking temperatures
  • person to person spread, usually during the acute diarrhoeal phase of the illness and contact with infected animals can also cause infection. Waterborne outbreaks have also been reported

Incubation period:

  • most commonly 12-48 hours but range of 4-120 hours has been reported
  • ingested dose will influence incubation period, symptoms and disease severity

Common clinical features:

  • symptoms include watery and sometimes bloody diarrhoea, abdominal pain, headache, nausea, vomiting and fever
  • duration of 4-7 days
  • usually resolve without treatment
  • septicaemia may occur and requires prompt hospitalisation and antibiotic therapy. The elderly, infants, and those with impaired immune systems are more likely to have severe illness and develop complications

Infectivity:

  • cases are considered infectious whilst symptomatic
  • however, organisms are excreted by convalescent carriers, asymptomatic carriers and (rarely) chronic carriers
  • cases with diarrhoea, infants and faecally incontinent adults pose a greater risk of transmission than do asymptomatic people
  • children aged <5 years may shed organisms for up to a year (median 10 weeks). Over the age of 5 years, the maximum duration of shedding appears to be up to 12 weeks (median 4)

Notes:

  • rates have fallen in the UK since the mid-1990s due to factors including greater public awareness about food safety, and the compulsory vaccination of the UK egg-laying flock against Salmonella Enteriditis
  • secondary cases are common in outbreaks
  • food handlers who practice good hygiene are very rarely responsible for initiating outbreaks
  • many reptiles, including those kept as pets, carry salmonella in their guts without exhibiting symptoms but may transmit infection to humans

Reference:

  • PHE (2019). Recommendations for the Public Health Management of Gastrointestinal Infections

Last edited 02/2020 and last reviewed 02/2020

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