Pregnant Swindon women and their unborn babies could be at risk from a potentially fatal food poisoning bug after four cases of listeria were reported in the town.

Tests have confirmed that three of the pregnant women became ill from the same food. It has not yet been determined what the source is, but expectant mothers are being warned to avoid foods such as pate and certain cheeses.

Investigations are continuing to establish whether the fourth woman was affected by the same source.

A fifth woman has been diagnosed, and although she does not live in Swindon, health officials believe there could be a connection to this area.

Symptoms of the bacterial infection mean that women affected could display flu-like symptoms and fever. In newborn babies listeria can cause meningitis and blood poisoning, and if left untreated can bring about stillbirths.

Dr Mark Evans, of Wiltshire's Health Protection Unit, has advised anyone at risk who feels unwell to contact their GP immediately or Great Western Hospital's maternity unit on 01793 604020.

The first case was brought to the attention of medics at the end of October. The link between the first two was established two weeks ago, but it was not until this week that tests confirmed the third expectant woman had the same strain of listeria.

The four Swindon women have since given birth three of which were premature and are said to be 'progressing satisfactorily' at home.

Chris Birdsall, spokesman for GWH, stated: "It's not the case that anybody was delaying making it public but tests had to be carried out to make sure they were the same strain of listeria.

"It's not an epidemic. We just want to let people know we are looking into it, and to remind pregnant women not to eat certain foods."

The last case of listeria in Swindon occurred in 2000 and there are an average of 120 cases in the UK every year.

Dr Mark Evans, of Wiltshire's Health Protection Unit, yesterday urged women to avoid eating certain foods while they are pregnant.

"Advice is given at antenatal classes and women should heed it," he said. "They should avoid eating pate, soft runny cheeses, and unpasteurised milk.

"We are working intensively with partners in the NHS and Swindon Council to identify the cause of the cluster.

"As yet we have no obvious source. We are interviewing the women to find out as much detail as possible about the foods they may have recently eaten.

"It may be one particular type of food. Even then it would not necessarily mean that every pregnant woman who ate that particular food would get listeria.

"There are multiple strains of the infection. The molecular typing that links the three cases is unusual, but that does not necessarily mean it is more serious than others."

Listeria does not usually cause disease in healthy adults, but certain groups are at particular risk and disease can be severe.

The immune system is mildly suppressed in pregnancy, which could explain why pregnant women are more susceptible.

Others most at risk include newly born babies, the elderly and those with impaired immune systems. Dr Evans added: "Listeria doesn't affect the mother as much as the baby. The symptoms can be relieved quite rapidly after a two-week course of antibiotics.

"Sometimes a woman will have intravenous treatment for two or three days in the hospital."

aemery@newswilts.co.uk

SOME FACTS ABOUT LISTERIA, AND FOODS TO AVOID

What foods should one avoid?

Pate, soft runny cheeses, such as Brie, Camembert and blue veined cheeses, such as Stilton and Danish blue.

All unpasteurised milk and its products.

Raw meat and poultry should be cooked thoroughly. Vegetables and salads should be washed thoroughly.

What causes listeria?

Listeria is a bacterium and has been known to cause disease in humans for many years.

It is found widely in the environment and worldwide, such as in soil and sewage. It is usually a food-borne disease and is known to be in foods including pate and blue veined cheese.

How common is listeria?

The last reported case of listeria in Swindon was in 2000.

Over the years 1993 to 2001 there have been between 90 and 140 reported cases each year in England and Wales. Between 10 and 26 per year have been pregnancy related.

Useful contacts:

NHS Direct: 0845 4647. Great Western Hospital 'maternity bleep holder': 01793 604020. www.amm. co.uk/pubs/fa_listeria.htm