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Salmonella

Salmonella

Named after the pathologist (Salmon) in whose laboratory it was first discovered in 1885, Salmonella is a bacteria found across the world.   We will look closely at the salmonella enterica type found inside intestines of warm-blooded animals – some of which humans eat for food and which can lead to food poisoning or salmonellosis

Transmission

Humans contract salmonella through contaminated animal food like meat, poultry and dairy products (milk and eggs). Infection usually occurs directly from ingesting food contaminated with enough salmonella organisms so as to trigger symptoms.

However, an infection can occur from fruit and vegetable products that were washed in contaminated water and more rarely directly from another person who has handled contaminated food.

Although salmonellosis can affect anyone, those with weaker immune systems such as children, elderly or others taking immune system suppressing medication like steroids are more vulnerable.

Further, travellers to places where food hygiene is less established are more exposed and so at higher risk of contracting salmonellosis.

Symptoms 

The bacteria takes 12-48 hours to multiply and trigger a reaction.

In the small intestine, Salmonella bacteria produce a toxin which affects intestinal walls, causing salts and sugars and so water to leak out. In the large intestine, the bacteria cause inflammation of the intestinal walls.

Together, this process causes the typical symptoms of stomach cramps and watery diarrhoea. Less common symptoms are fever, vomiting and blood/mucus mixed diarrhoea.

More rarely, salmonellosis can be invasive with bacteria crossing into the bloodstream infecting other organs such as the joints, lungs, kidneys or spleen.

Diagnosis 

Diarrhoea is a common symptom with many other causes.

One important disease to exclude is inflammatory bowel disease in which the stool has blood or mucus mixed in. This is not caused by an infection and requires further investigations.

Salmonella is distinguished from other bacterial causes of diarrhoea like campylobacter and shigella through stool cultures. This involves sending faecal samples in bottles (ideally on three different occasions) to the laboratory for microscopic examination.

The presence of salmonella bacteria confirms the diagnosis. However, it can take some time- even up to 8 weeks after symptoms have subsided in 1/3 of cases- for the bacteria to completely disappear from the stool.

Salmonellosis should be distinguished from enteric fevers of typhoid and paratyphoid, which are caused by different strains of salmonella. Their typical feature is high fevers rather than diarrhoea. Enteric Fevers are more common in tropical countries like India but can be very serious and require immediate treatment and antibiotics.

Treatment 

Symptoms typically last 3 to 4 days. During this time hydration is key to replace the water lost through loose stool.

Although it is better to allow the gut to continue to expel the bacteria through the loose stool, if the diarrhoea is uncontrollable and may lead to social embarrassment, then Loperamide can be taken for control.

Diarrhoea usually settles down by itself. However, sometimes antibiotics – such as Ciprofloxacin – may be needed if there are signs of salmonella spreading into the bloodstream.

Care should be taken to avoid antibiotics unnecessarily as they can prolong the course of the disease and in some people shift them into being a carrier of the disease. Antibiotics are also a risk factor for picking up infections because of how they affect the body’s own defences.

Further, to avoid spread to others, all clothes and bed sheets should be washed at high temperatures (as this is the only way the bacteria is killed) and crowds should be avoided for up to 48 hours after symptoms have stopped.

Prevention 

As ever prevention is better than cure!  So, to avoid salmonellosis it is important to take strict hygiene measures when preparing food. This starts from keeping clean food preparation surfaces to washing animal products thoroughly and away from other raw food alongside strict hand hygiene before and after.

© Syed Z Arfeen
Medical Advisor
July 2017