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Making Sense of ... Salmonella

(more correctly called Salmonellosis)

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Salmonella

What is salmonella?

Salmonellosis is an infection with the Salmonella bacteria; this article - incorrectly - refers to the infection as Salmonella, as that is the way most people do - even professionals.

Infection with Salmonella leads to fever, diarrhea, vomiting, and abdominal cramps, appearing at any time from 12 to 72 hours after infection. The symptoms willusually last from three to seven days, with full recovery without medical intervention in most cases. However, if the diarrhea leads to severe dehydrated, then hospital treatment may be required.

Where is salmonella usually found?

Salmonella is found all over the world, but with great variation in risk and incidence.

The type of salmonella usually associated with human infections is Non-Typhoidal Salmonella.

It is usually contracted by ingesting raw or undercooked meat, infected eggs and milk, as well as from egg products, plus certain reptiles can carry the bacteria on their skin.

A rarer form of salmonella called typhoidal salmonella can lead to typhoid fever. It is only confined to humans and is usually contracted through direct contact with the faecal matter of an infected person. It therefore mainly occurs in countries that lack effective systems for handling human waste.

How common is salmonella?

Very.

On 3 December 1988, Edwina Currie, a UK health minister said "Most of the egg production in this country sadly is now infected with salmonella." Sales of eggs plummeted 60 per cent overnight, and she was forced to resign. She was, of course, spot on, and while UK egg industry has since been 'cleaned up', there is still a real risk of the presence of the bacterium in imported eggs and many other foods.

But salmonella is almost always destroyed by cooking, and even if ingested, a fit person has a fair chance of resisting infection: where there are outbreaks, not all those who consumed the food go on to display symptoms.

In the US, in 2004, the incidence was 14.7 per 100,000 persons, continuing a steady decline over ten years.

How is salmonella transmitted?

The transmission of salmonella usually occurs by consumption of contaminated food.

The most common sources are beef, poultry, and eggs. Fruit, vegetables, dairy products, and shellfish - linked to poor food preparation parctices - have also been implicated.

Human-to-human and animal-to-human transmission can occur. For example, amphibian and reptile exposure has been associated with tens of thousands of infections annually in the United States. Recently, cats have also been implicated as a potential reservoir.

Although the infectious dose varies among strains, a large inoculum is probably necessary to overcome stomach acidity, other natural defences and competition with intestinal flora.

Salmonella, transmissible from vertebrate animals to man, is classified as a zoonosis.

Is there a genetic / familial / hereditary factor?

It is theoretically possible that some individuals may have reduced resistance to the infection, but no evidence has been found to support this so far.

Can salmonella be spread from person-to-person?

Yes, by poor hand hygiene and / or poor food preparation hygiene. Infection may also be passed on by the oral-anal route.

Who is most at risk from salmonella?

As with most infections, those at highest risk are infants, older people, and people with weak immune systems.

What are the symptoms of salmonella?

  • Diarrhoea or constipation.
  • Stomach cramps.
  • Nausea and vomiting.
  • Headaches.
  • Fever.
  • Blood in the faeces.

In mild infection, there may be diarrhoea two or three times a day for 48-72 hours. Most mild infections clear up completely four to seven days with rest and plenty of liquid.

More severe infection may cause excessive diarrhoea, leading to dehydration and other potentially serious health problems.

When is it necessary to contact a doctor?

  • If diarrhoea continues for more than 24 hours, or if it is frequent and intense.
  • If there are severe stomach cramps.
  • If there is blood in the faeces.
  • If there is fever of 38oC or higher.
  • If there are signs of jaundice
  • Dehydration.
  • Or simply if you are concerned - better safe than sorry.

What are the long term effects of salmonella?

Salmonellosis generally has no long-term effects. Recovery takes less than a week in most cases. More severe infections, and those affecting the young, the old and those with immunosuppression, may have a longer recovery time, and if there are concurrent serious problems - eg heart, liver or kidney problems, these conditions may deteriorate.

Occasionally, Salmonellosis may be followed by reactive arthritis, which may include a combination of three seemingly unlinked symptoms - an inflammatory arthritis of large joints, inflammation of the eyes (conjunctivitis and uveitis), and urethritis. A useful mnemonic is "the patient can't see, can't pee and can't bend the knee".

Reactive arthritis (ReA) used to be known as Reiter’s syndrome, after German physician Hans Reiter, before it became unfashionable to credit the pioneers of medicine. It is also known, severally as arthritis urethritica, venereal arthritis and polyarteritis enterica.

What is the mortality rate for salmonella?

Mortality in otherwise healthy people is very low, provided diagnosis is not unduly delayed, and appropiate supportive thereapy is available, should it be required. In those already weakened by concurrent conditions, it can add a significant risk.

It has been estimated that about 1,000 persons die each year with acute salmonellosis in the USA - with about 40,000 diagnosed with the condition.

How is salmonella diagnosed?

While often more serious than other forms of food poisoning, the symptoms are braodly very similar. So it's only laboratory tests that can confirm the diagnosis, and then go on to find the type of salmonella infection.

Is there a treatment for salmonella?

In most cases, no specific treatment is necesary. Fluids are encouraged, to replace those lost as a result of the infection; Oral Rehydration Salts can be useful to help restore electrolyte balance.. In a few cases, intravenous fluids may be required.

Intravenous antibiotics can be used, if required - but only after the sensitivity of the salmonella strain has been confirmed. This is because many strains now have wide antibiotic resistance, owing to the widespread, inappropriate overuse of antibiotics in healthy animals (to promote greater meat yield). Animal antibiotic abuse is still legal in many countries, despite the huge weight of scientific evidence of the potential for harm to the human food chain, and the spreead of resistant bacteria.

Is there a way to prevent infection?

In animal care, cleanliness and worker protection should be routine practice; those raising chickens,whetehr for meat of eggs should be extra careful.

In 1988, a UK health minister was sacked for daring to suggest that salmonella was rife in the British egg industry; despite the fact that the industry which rose united in horror, was well aware that she was correct, as has been proved since. More recently, other countries, inlcuding the USA, have had to come to terms with nationwide a salmonella presence in poultry. So far, no politician has dared to make the rather obvious link with farming methods, but that will happen eventually, of course.

In food preparation, simple common-sense hygiene is all that's needed:

  1. Keep raw meat away from cooked or ready to eat products
  2. Scrupulous hand hygiene
  3. Protective clothing - esp gloves - used by those who understand that gloves that have touched raw meat should not be used for anything else (duh!)
  4. Cooking meat and eggs at appropriate temperatures for the appropriate period
  5. Avoid giving raw/runny/half-cooked eggs to infants or a weak, frail or older person

What is the salmonella vaccine?

Vaccines have been developed for use in the meat industry, and has met with significant success in the UK. Despite this, the US FDA has (so far) not mandated its use. Which may or may not be linked with the recent recall of some 550 million eggs from two Iowa producers. 

Can salmonella be controlled environmentally?

  Yes; addressing farming methods, including the use of antibiotics, vaccines and good old fashioned cleanliness. So far most countries have nibbled at the edges of the problem, no-one has dared to undertake a serious review. I'm no conspiracy theorist, but it does strike me as odd that most countries manage to ensure farmers do not prosper, and then daren't demand higher standards for fear of adding to their woes. Maybe there's another way ....

Is there legal protection for workers and others?

Little specific law, but most countries have some health and safety law that can be used in civil action, even when prosecutions are rare.

What can be learned from history?

The sad truth is that most countries have learned from their mistakes, and can repeat them exactly; there is a wealth of solid scientific evidence as to how and why salmonella remains a serious danger; but so far little political will to deal with the real issues.

Bibliography and Further Information Sources

If your question has not been answered, email me at the address below, and I'll try to get the information you seek.

If this article hasn't answered your question, email me at the address below, and I'll try to get the information you seek. I regret I cannot assist with individual cases or essays and school projects, but if it's something I've missed, I'll be happy to try and help.

Article written by Andrew Heenan BA (Hons), RGN, RMN

First Published: 12 September 2010
Last updated: 7 March 2012
© Andrew Heenan 2010 et seq
 

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