Food Safety News – April 2011
Listeria – the ‘deli bug’
Last month Dairy Crest recalled one batch of Frijj Thick and Fresh Strawberry Milkshake due to low levels of listeria. So what is Listeria?
Listeria monocytogenes is a food poisoning bacterium which is often associated with foods such as cheese, milk , cooked meats, pate and smoked fish , consequently it is often referred to as the ‘deli bug’. Whilst it is not a common type of food poisoning the number of cases of illness from Listeria has been increasing over the last ten years.
It is unusual because it doesn’t cause the typical symptoms that we normally associate with food poisoning with the majority of cases suffering with a mild flu like illness. Listeriosis as with all types of food poisoning is often more severe in the very young, sick and elderly. It is also of particular concern to pregnant women because it can cause miscarriage or still birth.
Symptoms usually occur 3 to 4 weeks after consuming the infected food but in some cases it can be up to 90 days. This long incubation period often means it is very difficult to identify the contaminated food that was eaten by the individual because they are unlikely to remember what they consumed such a long time ago.
Listeria is normally found on contaminated vegetables, raw meats and unpasteurised milk which is why pregnant women are advised not to consume unpasteurised cheeses. If you serve unpasteurised cheese that isn’t cooked thoroughly you are advised to state on the menu that the cheese is unpasteurised so that it is clear to any pregnant or vulnerable customers. Listeria can be easily controlled by pasteurisation or cooking as it is very sensitive to heat treatment. Therefore there is no reason for pregnant women to avoid pasteurised cheeses.
As with all food poisoning bacteria Listeria can be found on foods that have been cooked or pasteurised if contamination occurs after processing. You must ensure that these high risk foods are protected from contamination by separating them from raw foods and making sure they are kept covered.
Listeria is also unusual because it can multiply quickly at higher refrigeration temperatures and is why the labelling on unpasteurised cheeses will often state that the product should be stored below 5oC which is cooler than the normal legal maximum of 8oC for refrigerated foods.
The Food Standards Agency in Scotland has recently commissioned some research to review practices in place to control Listeria during smoked fish production. There is concern over the cold smoking process because although there are controls in place in to reduce the growth of bacteria e.g. by addition of salt and cold smoking there isn’t a step in the processing that will kill any bacteria that maybe already on the product.
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