The federal government is acknowledging that a shipment of peanuts by the plant linked to a salmonella outbreak contained a "filthy, putrid or decomposed substance" later determined to be metal fragments.

That shipment was returned to the U.S. from Canada in April, months earlier than reflected in a federal tracking database.

According to government records, the rejected shipment was logged by the Food and Drug Administration but never tested by federal inspectors.

The incident took place in mid-September, the records show, weeks before the earliest signs of the salmonella outbreak that has sickened more than 500 people in the United States and may have killed at least eight.