WASHINGTON (AP) _ 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 other illnesses in Kansas, 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 found on equipment and in other locations in the plant 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. The agency said the listeria was found on surfaces that did not have direct contact with food.

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 facilities remain closed indefinitely as it cleans and sanitizes them.

Of the report, company spokesman Joe Robertson said when a test was conducted and there was a positive result for listeria, “our standard procedure is to stop, clean and sanitize and then re-swab the area. When we get a negative test (result), we feel like we are good about operating again.”

Robertson said the company takes safety seriously. Of Blue Bell’s procedures, he said, “In hindsight, we can see now that wasn’t always adequate.”

Violations in the Oklahoma plant include dirty equipment, inadequate food storage, food being held at improper temperatures and employees not washing hands appropriately, according to the report. Employees wore dirty shoes in the plant and soiled, porous wood pallets were used for ingredient storage and transportation. The FDA also said the company did not do enough testing for possible food contamination.

There were also violations reported at the Texas and Alabama plants. In Alabama, FDA investigators observed at least two employees working close to the food while wearing dirty clothing. In Texas, investigators saw condensation dripping directly into food and onto surfaces that came directly in contact with food. In all of the plants, the FDA found moist, dirty equipment and building infrastructure and disrepair that made cleaning difficult.

Blue Bell said it is making upgrades to equipment and building design as part of its cleaning.

Listeria generally only affects the elderly, people with compromised immune systems, and pregnant women and their newborn infants. It can cause fever, muscle aches and gastrointestinal symptoms and can be fatal. It also can cause miscarriage, stillbirth, premature labor, and serious illness or death in newborn babies.

The three deaths linked to the ice cream were in the same hospital in Kansas. All of those who died had already been hospitalized for other conditions.

Listeria bacteria are found in soil and water that can be tracked into a facility or carried by animals. Listeria can be very difficult to get rid of once it contaminates a processing facility, partly because it grows well in refrigeration. It is commonly found in processed meats, unpasteurized cheeses and unpasteurized milk, and it is sometimes found in other foods as well – listeria in cantaloupes was linked to 30 deaths in a 2011 outbreak.