A total of 130 people have now been affected by a massive outbreak of food poisoning in Bradford.

The outbreak, believed to have been caused by a virulent form of salmonella, has seen 49 people admitted to hospital in the last four days.

Twenty-three of them are still being treated for severe diarrhoea, sickness and dehydration.

There have now been more cases of salmonella poisoning in Bradford over the last four days than health chiefs would expect in a year.

The Health Protection Agency and environmental health officers from Bradford Council are investigating the source of the outbreak and putting in measures to prevent it from spreading.

Bradford Royal Infirmary, which has dealt with 46 in-patient cases, was today said to be stretched but coping with the outbreak.

Three patients who have visited Bradford recently have been admitted to other West Yorkshire hospitals with similar symptoms.

Communicable diseases consultant Dr Ruth Gelletlie is heading the Outbreak Control Team. She said: "It is uncommon to have an outbreak this severe.

"The illness has struck very acutely. The patients are not dangerously ill but ill enough.

"We wouldn't expect to see more than a couple of salmonella cases a week in Bradford. This is quite clearly an outbreak."

GPs have been informed of the outbreak and the team will monitor the number of cases while interviewing patients to try to find a common link.

Early results suggest the illness might have been caused by a particularly virulent strain of salmonella but tests are continuing.

Patients have been advised on how to avoid spreading the contamination and advised to stay at home for at least 48 hours after symptoms stopped.

Dr Gelletlie said not everyone who contracted the symptoms would need to go to hospital and that the numbers of fresh cases now seemed to be dropping.

She believed the outbreak seemed to have peaked on Monday and Tuesday.

She said: "The hospital seems to be coping very well and we are in constant contact with them.

''In Bradford 46 people have been admitted into hospital, which has clearly stretched it, but they have reorganised their schedule. Half of them have now gone home and all are now improving."

Dr Gelletlie said it was too early to say whether the salmonella had come from a single source.

Patients experiencing frequent diarrhoea or vomiting are advised to contact their GP for advice. General health advice for people who are concerned is available from NHS Direct on 0845 4647.