Blue Bell said the bacteria responsible for shutting down its plants last year may be at its home plant in Brenham in Central Texas.
The company said suspected Listeria species may be present at the plant, but not in the areas where ice cream is produced.
"We continue to extensively clean and sanitize those areas and make additional enhancements to the facility and our procedures based on the environmental test results. To confirm that our robust environmental program is effective, and that our 'seek and destroy' goals are being achieved, we expect to periodically find microbiological indications in our facilities," Blue Bell said in a statement.
Blue Bell shut down all three production facilities in Texas, Alabama and Oklahoma in April and all ice cream was recalled after its treats were linked to 10 listeria cases, including three deaths in Kansas. Listeria bacteria can cause serious illness, especially in older adults, pregnant women and people with weakened immune systems.
The company upgraded its facilities, put safer new procedures in place and retrained employees before returning to store shelves in Texas and across the south in the fall.
Still, the Department of Justice is investigating the outbreak, alleging the comping knew as early as 2013 that at least one plant was contaminated.