U.S. Agriculture Department officials have launched an internal investigation into how the agency handled reports of serious problems at a Boar's Head deli meat plant tied to a deadly listeria outbreak, a lawmaker said Tuesday.

Sen. Richard Blumenthal said that USDA Inspector General Phyllis Fong is looking into whether federal investigators and Virginia state inspectors responded appropriately to dozens of reports of problems at the factory, including mold, insects, dripping water and meat and fat residue on walls, floors and equipment. Inspection reports dating back at least two years indicated that the conditions could pose an "imminent threat" to food safety.

The action came in response to a Sept. 5 letter from Blumenthal demanding an investigation, he said.

"USDA took virtually no action — allowing Boar's Head to continue business as usual at its chronically unsanitary Virginia plant — despite finding repeated serious violations," the Connecticut Democrat said in a statement.

At least 10 people died and nearly 50 were hospitalized in 19 states since May after eating listeria-contaminated Boar's Head products, including liverwurst, according to the U.S. Centers for Disease Control and Prevention. After recalling more than 7 million pounds of deli meat distributed nationwide, Boar's Head officials shuttered the plant in Jarratt, Virginia, and permanently stopped making liverwurst.

Officials with Fong's office did not immediately confirm the investigation. Blumenthal declined to release the agency's response. He said the internal investigation would evaluate the handling of recurrent problems and whether state inspections properly reduced the risk of tainted products entering the food supply.

The Boar's Head plant was inspected under a program that allows state inspectors to act on behalf of the federal agency.

In addition to the internal investigation, Blumenthal and Connecticut Rep. Rosa DeLauro last month asked the Justice Department to investigate whether criminal charges were warranted.

Officials with USDA's Food Safety and Inspection Service have refused to share documents regarding the agency's inspections and enforcement at the plant, plus inspection reports from eight other company factories across the country. The agency denied Freedom of Information Act requests submitted by The Associated Press, saying releasing the records could "interfere with" and "hinder" potential law enforcement investigations. The AP is appealing the denial.

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