London (BBN)-Some 73% of fresh shop-bought chicken tested positive for food poisoning bug campylobacter in a year-long study by the Food Standards Agency (FSA).
The survey tested about 4,000 samples of whole raw chickens bought from UK retail outlets and independent stores, reports BBC.
All of the major retailers failed to reach industry targets to reduce the bug over the period of the study.
But the FSA said Marks & Spencer, Morrisons, the Co-op and Waitrose had since seen a fall in contamination.
The four retailers carried out their own case studies to show how their plans to reduce levels of campylobacter are working, the results of which have also been published.
This data - from tests carried out on more recent samples than the FSA study - showed "significant decreases in the incidence of campylobacter on their raw whole chickens", the agency said.
Campylobacter is the most common form of food poisoning in the UK, with an estimated 280,000 people a year affected by it.
Poultry is the source of most cases - although cooking meat properly will kill the bug.