According to a statement released last month by the federal authorities, Nebraska Beef Ltd, which is related to almost 50 sicknesses caused by contaminated ground beef, had made the necessary changes after a recall so as to guarantee customers its products are safe.

Less than a month later, the same meat plant recalled 1.2 million pounds of the fresh ground beef it sold between June 2 and August 6, due to the fact that it may be tainted with E. coli bacteria. The beef products might have triggered 31 people falling ill in U.S. states on the East Coast and in the Midwest: New York, California, Idaho, Colorado, Massachusetts, Virginia, Connecticut, New Mexico, Ohio, Pennsylvania and New Jersey.

Libba Letton, a spokeswoman for Whole Foods, the world's largest retailer of natural and organic foods, said that tests haven’t found tainted beef at the grocery chain.

As proclaimed by the Austin, Texas-based company, none of the tainted meat is currently put on the market in any of its retail establishments. However, the investigation of possible E. coli outbreaks continues.

E. coli bacteria can cause serious food poisoning in humans. The infection can trigger stomach cramps, diarrhea, dehydration and in most severe cases, kidney failure. If present, E. coli bacteria should be killed by cooking meat to an internal temperature of more than 160 degrees.