21.   Preliminary tests had detected the bacteria in a substance inside the letter.

22.   South Korean quarantine officials detected E. coli bacteria last week on the surface of the imported frozen and sliced beef.

23.   The case prompted the U.S. Department of Agriculture to send its own experts to examine how South Korea detected the bacteria on the U.S. meat.

24.   The building where both worked was closed after the bacteria also were detected there.

25.   The same bacterium has been detected in the fatty plaques that clog heart arteries, though researchers do not yet know if it is responsible for the clogging.

26.   The state government has distributed water purification tablets, chlorinated wells, and taken water samples to detect the bacteria.

27.   But investigations at the farm conducted in July and August failed to detect the bacteria at production facilities, nearby waterways or from farm workers, the report said.

28.   But investigations at the farm conducted in July and August failed to detect the bacteria at production facilities, nearby waterways or among farm workers, the report said.