Health experts worried as listeria cases rise by 80%

There are concerns that levels of the food poisoning bug – which can be spread by mice – are likely to increase further with moves to fortnightly waste collections.

Listeria is often associated with chilled ready meals, soft cheese, pâté and cold meat.

The number of cases which required hospital care in the first 21 weeks of this year reached 79, according to the Government's Health Protection Agency.

Groups vulnerable to the bug are pregnant women and the elderly or sick whose immune system is compromised. Nine of the cases reported were pregnant women who can pass on the infection to their baby in the womb. This can trigger miscarriage or serious illness in the child.

The HPA has begun an investigation of the cases to see if there is a common source. Most were in the North East, Wales and London, but there have been others in every region.

Of those with the illness 55 were aged over 60 and likely to have been suffering other chronic conditions. Listeria was seen as a contributing factor in the deaths of a number of these patients.

The Food Standards Agency has issued guidance to the vulnerable on how to protect themselves. They should avoid eating soft ripened cheese and other blue-veined varieties, as well as pâté.

If those in these groups show symptoms such as fever, muscle aches, nausea or diarrhoea, they are advised to contact their GPs.

Most food poisoning bugs are swift-acting and cause violent stomach upsets. But the symptoms of listeria can take 90 days before they show.

In March, an alert was issued after listeria was found in sandwiches destined for schools, hospitals and tourist attractions in the South.

More than 200,000 sandwiches produced by Kent-based Anchor Catering were at the centre of the alert.

There is no link between this investigation and the other listeria cases being looked at by the HPA.

Listeria is widespread in the environment and can be found in raw food, soil, vegetation, sewage and in the droppings of many mammals, birds, and fish. Up to 5 per cent of the population may be carriers of the disease but do not become ill.