UPDATED: May 11, 2015

Texas-based Blue Bell Creameries, which pulled all its products from stores in April, was aware one of its production facilities tested positive for listeria more than two years ago, according to recent documents released by FDA.

But no recalls were issued until this year, after an outbreak of Listeriosis was linked to the company’s ice cream products.

On Thursday FDA released results of its investigations into Blue Bell plants in Oklahoma, Texas and Alabama. The documents detailed 17 presumptive positive tests for listeria at the Oklahoma plant dating back to March of 2013 where the bacteria was first found on non-food contact surfaces. Subsequent tests were positive for the presence of listeria around the plant and on equipment.

But FDA says it was unaware of the contamination or test results until the agency began its investigation this year. According to the government agency, companies need only report their findings when they have a "reasonable probability" the food will cause illness, but Blue Bell's results indicated listeria was found on surfaces and not in the ice cream products.

In a statement obtained by USA Today, a company spokesperson said:

“Several swab tests did show the presence of listeria on non-food surfaces in Blue Bell's Broken Arrow plant in 2013. As is standard procedure for any such positive results, the company would immediately clean the surfaces and swab until the tests were negative. 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."

Other observations noted by FDA in its inspections of the plants included employees not thoroughly washing hands, condensation dripping into products, coliform over permitted levels and inadequate cleaning of equipment.

Since the recall was initiated, Blue Bell has collected approximately eight million gallons of ice cream and ice cream products. On Thursday, the company said it is unsure when it will be able to return product to store shelves, but anticipates a minimum of several months. Blue Bell previously hoped to restore some production this month. The company said the process of updating, cleaning and sanitizing its four production facilities, in addition to training employees and implementing new programs and procedures, will take longer than anticipated.

Blue Bell says each plant will have its own timetable and production may resume in some locations before others.

 “Blue Bell is committed to a thorough process that will ensure the highest quality and safety of our products for our customers going forward,” the company said. “We know we have to get this right, and we intend to do so.  That is our top priority.”