WASHINGTON — Blue Bell ice cream had evidence of listeria bacteria in its Oklahoma manufacturing plant as far back as March 2013, a government investigation found. The Texas-based company continued to ship ice cream produced in that plant after what the Food and Drug Administration says was inadequate cleaning.

Three listeria deaths in Kansas are now linked to the ice cream, along with seven illnesses in Texas, Oklahoma and Arizona. Blue Bell Creameries recalled all of its products last month, following several smaller recalls.

The FDA on Thursday released results of its investigations into Blue Bell’s plants in Oklahoma, Texas and Alabama after a Freedom of Information request by The Associated Press. The most extensive violations were found in Oklahoma, where the FDA listed 17 separate positive tests for listeria on equipment from March 2013 through February 2015.

The FDA would not say who conducted the tests, but it noted that Blue Bell sent “presumptive positive” listeria samples to a third party for confirmation on at least two occasions in 2014. The auditors re-tested the samples and came back with the same results.

Blue Bell continued to have presumptive positive listeria results in the Oklahoma plant even after the daily cleaning and sanitizing treatments of equipment and facilities, the FDA wrote Blue Bell in the report.

Neither Blue Bell nor the FDA has said why the Oklahoma plant was not closed after repeated findings of listeria.

FDA officials have so far declined to discuss the report or the history of the testing.

After the test results were made public, Blue Bell CEO Paul Kruse said in a statement it would be “several months at a minimum” before its ice cream is back in stores. The company had said earlier that it expected to be back up and running this month.

Blue Bell said in its statement that its three facilities remain closed indefinitely.