Asda has the highest rate of the food poisoning bug campylobacter in its fresh chickens, according to figures published by the Food Standards Agency.
The FSA found 80.4% of samples from the supermarket tested positive, with 29.7% of it being at the highest level.
This was followed by Co-op where 78.1% of samples failed to pass the test, 75.8% at Morrison's, 73.8% at Waitrose and 69.7% at Sainsbury's .
Results from M&S showed 67.1% contained the bug, which is the most common form of food poisoning.
While Britain's largest supermarket Tesco had the lowest levels of campylobacter, with 66.5% of samples testing positive.
The tests were carried out on more than 4,000 samples of fresh chicken between February 2014 and February this year.
As well as the actual chicken containing traces of campylobacter, 7% of all packaging also tested positive for the bug.