An investigation into the safety measures at Cadbury’s Marlbrook plant in Herefordshire following its recall of one million bars has discovered an unreported Salmonella outbreak there in 2002.

Public health officials in the UK have revealed that the Cadbury’s factory at the center of the salmonella scare was infected with the same strand of the disease four years earlier.

The Food Standards Agency disclosed news of the 2002 contamination in a report that said the food giant had failed to adequately assess the risk of salmonella in its chocolate through the use of "unreliable" methods that may have underestimated the scale and likelihood of contamination.

Since March, 31 people, 3 of whom were hospitalized, have become ill with the same rare strain of salmonella food poisoning.