Experts unable to explain increase in number of listeriosis cases

Twice as many people contracted listeriosis – a food-borne infection – in 2009 compared with the previous year.

The latest figures, from the National Food Institute at the Technical University of Denmark (DTU) show that Denmark has the highest number of cases of the rare and potentially lethal bacterial disease.

Some 97 people in 2009 were registered as infected with listeriosis, which is particularly prevalent among the elderly, new-born babies, pregnant women as well as people with a weakened immune system.

The listeria bacteria causes a number of serious symptoms such as blood poisoning and meningitis; in pregnant women the infection sometimes spreads to the foetus.  The death rate is high – 20-30 percent of patients infected – especially among the elderly and those with a weak immune system.

Listeria bacteria can infect humans when they eat contaminated food such as cheeses, smoked fish and cold meats often. Unlike many other food-borne diseases, the bacteria can thrive at fridge temperatures.

Jens Kirk Andersen, an expert from the National Food Institute said that it is often difficult to identify the source of listeria infections because it may take anything from two days to two months before symptoms appear.

‘Understandably enough many people infected with listeria are unable to remember which food items they ingested after so long,’ he said.

A group of DTU researchers are currently investigating why the number of infections has shot up, but so far they have been unable to pinpoint the cause.

Andersen believes that new eating habits by the elderly may be significant.

‘However this can’t be the whole explanation,’ he added. ‘That is why there is a great need for more information in this area.’

Statens Serum Institut has registered 26 cases of listeriosis so far this year, roughly the same level as that recorded in 2008.

Listeria is found in uncooked meats, uncooked vegetables, unpasteurized milk, foods made from unpasteurized milk and processed foods.

Pasteurisation and sufficient cooking kill the bacteria, but contamination may also occur after cooking and before packaging.