Contaminated Cadbury's chocolate was the most likely cause of an outbreak of salmonella poisoning, the Health Protection Agency has said.
Cadbury will increase its contamination testing levels
About 36 out of a total of 56 cases of the illness reported between March and July could be linked to the product.
Cadbury's recalled one million chocolate bars in June because of salmonella fears.
The firm has blamed a leaking pipe at its Marlbrook plant in Herefordshire for the salmonella contamination.
The seven brands affected by the recall were the 250g Dairy Milk Turkish, Dairy Milk Caramel and Dairy Milk Mint bars, the Dairy Milk 8 chunk and the 1kg Dairy Milk bar as well as the 105g Dairy Milk Buttons Easter Egg and the Freddo bar.
A cleaning operation is up and running at the plant, near Leominster, to ensure no salmonella remains, the company said.
In a statement, the Health Protection Agency said 13 of the people it had interviewed reported eating Cadbury's products.
Another person said they had eaten confectionery, but did not know the brand.
The National Public Health Service in Wales also reported a person who had eaten a Cadbury's product.
The agency's Outbreak Control Team (OCT) said: "After carefully considering all the available evidence the OCT concluded that consumption of products made by Cadbury Schweppes was the most credible explanation for the outbreak of salmonella Montevideo."
The agency also noted the number of cases of reported salmonella dropped following the firms voluntary product recall and said the geographical distribution of cases suggested the outbreak was caused by a nationally distributed food.
Cadbury's has agreed to improve its testing procedures after experts working for the Food Standards Agency said they were not up to modern standards.
The firm originally said it had recalled the bars purely as a precautionary measure.
"The levels are significantly below the standard that would be any health problem, but we are taking this measure as a precaution," a spokesman said at the time.