A government investigation has revealed that Blue Bell  was aware of listeria contamination in one of its plants as early as two years ago, but did not issue recalls.

According to a Food and Drug Administration report released Thursday, surfaces at Blue Bell's creamery in Broken Arrow, Oklahoma tested positive for listeria five times in 2013, 10 times in 2014, and once in January of 2015. Contaminated surfaces included the floor in front of a freezer, a drain behind a flavor tank, a water hose in front of a filler. Some surfaces listed in the report were redacted in Thursday's report.

Blue Bell told the New York Times that it took measures to clean these surfaces, but that their efforts were insufficient.

“As is standard procedure for any such positive results, the company would immediately clean the surfaces and swab until the tests were negative,” a statement to the Times said.

“We thought our cleaning process took care of any problems, but in hindsight, it was not adequate, which is why we are currently conducting such a comprehensive re-evaluation of all our operations.”

However, the FDA's report says that Blue Bell failed to make recommended adjustments to its cleaning procedures and lists examples of unsanitary practices observed by investigators.

“The plant is not constructed in such a manner as to prevent drip and condensate from contaminating food, food-contact surfaces and food-packaging materials,” the report reads.

Neither the FDA nor Blue Bell has commented on why the plant was not closed as a result of the findings in the report.