An Abbott Laboratories manufacturing plant in Sturgis, Mich., in 2010. Brandon Watson/Sturgis Journal via AP, File

The Department of Justice has opened a criminal investigation into an Abbott Laboratories plant in Sturgis, Mich., that was at the heart of last year’s baby formula shortage, a spokesperson for the company confirmed Friday.

The “DOJ has informed us of its investigation and we’re cooperating fully,” said Scott E. Stoffel, a spokesperson for Abbott.

Last February, Abbott recalled Similac and other powdered formulas that were made at the Michigan plant, which was later shut down following a Food and Drug Administration inspection. The FDA found evidence of previous bacterial infections and of workers handling materials without washing hands.

The closure of that plant worsened a nationwide shortage that left parents unsure where they would find more baby formula. It came four months after a whistleblower had submitted a report to the FDA alleging unsanitary conditions at the Sturgis plant.

The agency later investigated reports that as many as nine children had died after allegedly drinking formula from the plant, but it was unable to identify the source of the infections, according to documents released last summer. The plant restarted Similac production in August that year.

The Wall Street Journal first reported the details of the DOJ investigation.

Abbott is one of four major companies that control some 90 percent of the infant formula supply in the United States.

“I have to say it’s about time,” said Steve Rathke, a retired attorney who tried civil cases against the formula companies on behalf of families whose children were sickened by Cronobacter sakazakii, a germ found in dry foods such as powdered baby formula. “I wish they’d done it 10 years ago.”

Abbott said last summer that no causal relationship had been established between its products and any of the reported deaths.

“Abbott conducts microbiological testing on products prior to distribution and no Abbott formula distributed to consumers tested positive for Cronobacter sakazakii or Salmonella. All retained product tested by Abbott and the FDA during the inspection of the facility came back negative for Cronobacter sakazakii and/or Salmonella. No Salmonella was found at the Sturgis facility,” Abbott said in a statement at the time.