Listeria: what is Listeria and how are patients affected?


News reports today have today focussed on listeriosis. And several brands of frozen vegetables have been recalled due to risks of listeria contamination.  So why all the concerns?  I thought a quick overview of Listeria may help calm the hype and also help those who are concerned about possible infection.

The main concern with this particular organism is that although it is transmitted through being eaten, unlike most organisms transmitted this way,  it can result in a severe systemic illness that does not stay confined to the gastrointestinal tract.   As such patients often present with complaints of feeing generally unwell with fevers aches and pains rather than with vomiting and diarrhoea.  In severe cases of infection this bacteria can cause meningitis and and stillbirth.

The bacteria that causes Listeriosis is called Listeria monocytogens.  It is is found mainly in animals such as sheep and cattle, but can also be found in the soil and the environment.  Interestingly, this organism can be found in the normal flora of the gut of healthy individuals without casuing diease, making it an ‘opportunistic pathogen’.  However, there are two patient populations who are at particular risk of infection once this bug gets out of hand.  First are those who have a depressed immune system.  This immunosuppression could be due to disease or due to medication use.  The second group of vulnerable patients are pregnant women.    It is estimated that up to one in five infections may be fatal if left untreated and this number can be even higher during a significant outbreak.  The source of infection in humans is mostly from ingestion of contaminated foods; most commonly “ready made meals” that have been contaminated during the manufacturing process.

The most common patients who suffer from listeria infection include pregnant women, the elderly, patients who have a suppressed immune system (for example by medications such as corticosteroids) and those patients with cancer, diabetes, HIV, or kidney disorders.  Typical symptoms are fevers, back ache, generalised muscle aches and pains as well as vomiting, nausea and diarrhoea.  If at patient develops meningitis then they could experience headaches, confusion, neck pain and irritation as well as seizures, difficulty walking, and personality changes.  In extreme cases this bacteria can attach to the heart valves- a condition known as infective endocarditis.  Because the pathogen enters the blood stream it can end up anywhere causing infection in the eyes, the lining of the lungs, the gallbladder and even in the bones.

The good news is that treatment is relatively straight forward with most patients requiring two to three weeks of antibiotic treatment.  This being sufficient to treat most cases uncomplicated cases.

Prevention however is always better than cure!

To prevent infection the following tips can be used:

  • separate uncooked meat from vegetables and cooked foods
  • all raw food should be cooked thoroughly
  • avoid raw and unpasteurised milk and milk products
  • make sure utensils are washed thoroughly in hot soapy water after preparing food
  • return any products that are listed in the recall

So if you have any concerns regarding possible infection please see your GP or Emergency Department for prompt assessment and diagnosis.  This is especially important if you fall into one of the vulnerable population groups described above.

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