British officials have issued a food poisoning alert after learning that nearly 250,000 packed sandwiches could be contaminated with the listeria bacterium.

The Times of London said that Britain's Food Standards Agency issued the warning Friday after it was revealed that ready-made sandwiches from the Anchor Economy, Anchor Gourmet or Pomegranate labels may be potentially dangerous.

The health group found that the bacterium may have contaminated the foods for more than three weeks and its effects may not be readily apparent for up to three months after ingestion.

While most healthy adults are not significantly at risk regarding the listeria, the Health Protection Agency warned that pregnant women specifically were.

Other high-risk groups include the elderly, infants and the physically ill.

No related illnesses were reported since the warning was issued.

The paper said that the possibly infected sandwiches were mainly sold to schools, hospitals, canteens and sports centers in Southern England.

Copyright 2007 by United Press International