A fatal salmonella outbreak across the British Isles that has infected 90 people may be linked to sandwiches sold by Subway.

Laboratory tests have shown a link between cases of illness and one of the US sandwich chain's ingredient suppliers. Cooked beef, chicken and bacon have been impounded at Dawn Farm Foods in Co Kildare, Ireland.

As a precaution, Subway has removed batches of its Philly Style Steak and Chicken Fajita sandwiches from its 1,250 shops in the UK and Ireland. Other sandwich shops may also have bought the potentially contaminated meat.

The discovery could end the mystery of what had caused the outbreak of a new strain of Salmonella agona. The average age of victims has been 29 but a one-year-old baby has also fallen victim to the bug. Salmonella poisoning was a contributory factor in the death of a woman in her seventies at Royal Liverpool University Hospital.

Salmonella is usually contracted from contaminated meat which has not been cooked at a sufficiently high temperature. Inquiries by the Food Safety Authority of Ireland (FSAI) centre on the heat treatment applied at the Irish plant.

In an apparent breakthrough in the inquiry into the outbreak, the FSAI said: "Whilst the investigation continues to seek to establish the exact source of the outbreak, laboratory testing of foods is providing evidence of a possible link with Dawn Farm Foods Ltd, Naas, Co Kildare and some of its products.

"Information gathered by the FSAI suggests that a potentially contaminated beef product was supplied to the Subway chain of food outlets and the FSAI has received assurance from Subway that this product has been removed from sale.

"In light of this, as a precautionary measure in the interests of public health, all products processed on the same production line as this beef product at Dawn Farm Foods are being withdrawn."

In a statement, Subway confirmed that Dawn Farm Foods was one of its ingredients suppliers and the possible link with the ongoing investigation into the salmonella outbreak. It stressed that no other products were affected and that it had found alternative suppliers.

Salmonella causes vicious stomach cramps, diarrhoea, vomiting and fever and can kill people with weak immune systems. Each year 12,500 cases of the bug are reported in England and Wales. However, public health officials believe they are only a fraction of the total, meaning that hundreds may have fallen victim to the latest outbreak.

It is thought the cooked food supplied to Subway would have been reheated in store. Alan Reilly, a spokesman for the FSAI, said: "This is a highly complicated outbreak investigation, focusing on products from one thermal processing line with a complex food distribution chain."