Iowa egg producer Centrum Valley Farms was sent a warning letter on August 14 by the Food and Drug Administration after a routine government safety inspection discovered Salmonella Heidelberg in two of the company's barns in May. Centrum Valley said it diverted a number of eggs from the consumer market "in the interest of egg safety" and withheld them until they tested negative for the bacteria four times and were eventually approved for sale by the FDA.

The plant is already under strict oversight because it was one of several in northern Iowa implicated in the 2010 Salmonella outbreak, which led to the recall of more than 500 million eggs nationwide and sickened roughly 2,000 customers. "SH has caused several egg-associated outbreaks resulting in human illness and at times death," said the FDA in its letter. "Given this body of evidence, the FDA considers SH within a poultry house environment to be a public health threat. We acknowledge that you have been working with the FDA to address this situation."

Centrum Valley is in the process of responding to the FDA's findings, which also include deficiencies in the company's testing for Salmonella and its Salmonella prevention plan. "Providing safe, high-quality eggs to Centrum Valley Farms customers is our obligation," said Chief Operating Officer Steve Boomsma. "We have already taken corrective actions." The FDA gave Centrum Valley 15 working days to issue a response outlining "specific things you have done or plan to do to correct these violations and prevent their recurrence."