(UPDATED COVERAGE, Feb. 7) A warning letter from the Food and Drug Administration, made public Feb. 5, indicates the agency is still concerned about listeria contamination found in July at a fresh-cut facility that supplied apple slices to McDonald"s and Burger King restaurants.

The warning letter to Missa Bay LLC dated Dec. 10 gave company officials 15 days to respond.

UPDATED: FDA hasnTamara Ward, FDA press officer, said Feb. 7 the company responded to the December letter but that she could not release details because the investigation is ongoing.

Ward said the FDA sent the letter in December because the company"s officials did not provide followup documentation last fall regarding their listeria control program or their new facility. Ward said the company has since been in communication with the FDA.

Tristan Simpson, marketing director for Missa Bay"s parent company Ready Pac Foods Inc., however, said she has written documentation from the FDA that the case is closed.

The FDA"s December letter references the agency"s investigation from July 27 through Aug. 23 at the Missa Bay facility in Swedesboro, N.J. The agency initiated that action after notification from the U.S. Army Public Health Command that a sample of Missa Bay sliced apples tested positive for listeria.

In August 2012, Ready Pac and Missa Bay recalled almost 300,000 cases and another 296,000 individual packages of fresh-cut fruit, vegetable and sandwich products because of possible listeria contamination.

The FDA"s December warning letter states that finished product samples plus 27 environmental samples taken at the Missa Bay facility during the 2012 investigation were positive for listeria. Those included samples from food contact surfaces, the non-browning solution used on slices apples, and non-food contact surfaces.

Missa Bay sent a letter to the FDA on Sept. 5 stating it would develop and implement a redesigned listeria control program by Sept. 8, according to the FDA"s Dec. 10 warning letter.

The company"s letter also told the FDA it was moving its apple processing to a "new and redesigned apple processing facility." FDA"s Ward said the company indicated it was switching from a heat treatment process to a three-stage filtration system.

The 2012 recall included 29 products shipped to retailers and foodservice operations in 36 states and Washington, D.C.

In addition to apple slices for McDonald"s and Burger King, products packed under the Wawa brand, Ready Pac label, Wegmans label and Hannaford label were included in the recall.