Food safety investigators are inquiring into whether a range of Easter eggs and boxes of chocolates on sale this year were contaminated with a salmonella bug.

The action comes after data from the Health Protection Agency showed that food poisoning incidents of salmonella Montevideo — the bug that led Cadbury to recall a million chocolate bars ten days ago — peaked in the weeks after Easter and Mothering Sunday. One Easter egg, the 105g Cadbury’s Dairy Milk Buttons egg, was part of the recall of seven products.

Health chiefs have been unable to establish a specific link between the human cases and eating any particular food, but they cannot ignore the peaks of food poisoning coinciding with celebrations at which eating and giving chocolate is a tradition. Tests are therefore being rerun on samples from at least 30 other product lines to check for the bacteria.

This work is being carried out in parallel by environmental health officers at Birmingham City Council and Cadbury’s own scientific team. The company insists that it has found no evidence of any other contamination in any other of its 2,500 product lines. However, it is not giving details of other products that are subject to the new tests.

It is understood that at least 70 per cent of Cadbury’s chocolate bars have now been recalled from more than 55,000 shops.

The agency has revealed that the highest number of cases of the bacteria strain, known as SmvdX07, were in week 16, which started on April 17, Easter Monday, and week 20, which started on May 15, the day after Mothering Sunday.

Three people admitted to hospital suffering from infection by the strain are believed to have recovered.

Cadbury is attempting to go through its data to find out exactly when the seven product lines named in the recall were distributed for sale.

The affected products are 250g Dairy Mild Turkish, Dairy Milk Caramel, Dairy Mild Mint bars, the Dairy Milk 8 Chunk, the 1kg Dairy Milk bar, the 105g Dairy Milk Buttons Easter Egg, and the 10p Freddo bar.

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