Consumer groups in the US questioned the length of time that it took the USDA to make a link between a recent listeria outbreak and a strain of listeria found at a Pilgrim's Pride plant in Franconia.

Pilgrim's Pride recalled 27.4m pounds of deli meat on Sunday after concerns that it may have become contaminated with listeria while being processed at the plant.

On Tuesday the USDA confirmed that the Franconia plant was the most likely source of that particular outbreak.

Consumer groups have accused the USDA of being too slow in announcing the link.

The USDA also suffered similar accusations over the ConAgra recall in July. In that case the USDA admitted it had not acted quickly enough after discovering the presence of E.coli in a ConAgra meat sample, reported Reuters.