Food safety experts were last night trying to trace the source of an outbreak of a new strain of salmonella that has spread throughout the British Isles.

Ninety people have caught the food poisoning infection in England, Wales, Scotland, Northern Ireland and Ireland since February. Most sufferers have been young adults, but a baby and a 79-year-old have also been infected. Given the wide geographical spread of cases, the bacteria may have been carried by a commercial food product.

Salmonella is a food-borne gastro-intestinal disease contracted by eating contaminated food, usually meat which has not been cooked at a high enough temperature to kill off the bacteria. Victims suffer stomach cramps and diarrhoea and occasionally vomiting. Most people recover from the illness within a week but it can occasionally be fatal among those with low immune systems, such as children and the elderly.

The Food Standards Agency advised people to keep their kitchen and hands clean and always cook food thoroughly. When eating out, they should make sure food is "piping hot".