Blue Bell Creameries told federal inspectors that it believes Listeria spread at its Oklahoma plant through a drainage system, but the company said it couldn’t identify a single source of Listeria that contaminated equipment at its flagship facility in the Central Texas town of Brenham.

The Texas-based ice cream company revealed the findings in documents sent to the Food and Drug Administration, KXAS-TV in Dallas-Fort Worth reported Friday.

In its filing to the FDA, Blue Bell said cleaned equipment that came into contact with products made at its Broken Arrow, Oklahoma, plant was being stored in a small room with a floor drain. The company said an investigation revealed that particles at the plant may have carried listeria and washed into the building’s drainage system, gone through the room’s drain and settled on the clean equipment.

“We believe that this mechanism — particles emitted from a drain — was the most likely source of listeria,” Blue Bell wrote in the February filing.

The company said it no longer uses the room for equipment storage, and that the drain was removed and the floor replaced.

Blue Bell also told the FDA that it believes listeria likely entered its Brenham plant from “various potential sources” and settled on some pieces of equipment, but that investigators “could not identify a single common source of listeria in the facility.”

The company said it focused on cleaning affected pieces of equipment or removing it altogether, cleaning and sanitizing the plant and enhancing sanitation procedures and testing programs.

“We identified and implemented specific corrective actions to address the likely source, and adopted comprehensive facility-wide programs to enhance our overall ability to confront any possible sources of contamination,” Blue Bell spokesman Joe Robertson said Sunday.