The bacteria campylobacter contaminated 70 per cent of fresh shop-bought chickens stocked by major retailers.
The Food Standards Agency (FSA) said the cumulative results from the first two quarters of its year-long survey of fresh chickens found 70 per cent tested positive for the presence of campylobacter, up from 59 per cent in August.
Almost a fifth of all chickens (18 per cent) tested positive for the bug above the highest level of contamination, or 1,000 colony forming units per gram (cfu/g), and 6 per cent of packaging tested positive - up from four per cent in August.
The FSA also named rates among retailers for the first time, revealing that Asda sold the highest percentage of chickens contaminated with campylobacter at 78 per cent, with 28 per cent showing the bug above the highest level of contamination and 12 percent of packaging testing positive.
Almost three-quarters of chickens (73 per cent) sold by the Co-operative tested positive, followed by Morrisons, Sainsbury's and Waitrose (69 per cent), Marks & Spencer (67 per cent) and Tesco (64 per cent).
Individual figures for the discounters Aldi, Lidl and Iceland were not reported because their market share was based on 2010 figures and deemed too small, but the overall rate of campylobacter contamination among all retailers other than the major supermarkets was 76 per cent.
The FSA said Tesco was the only major retailer which had a lower incidence of chicken contaminated with campylobacter at the highest level compared with the industry average.
Asda was the only major retailer with a higher incidence of contaminated chicken.
However, the FSA said the results suggested that none of the retailers was achieving the joint industry end-of-production target for reducing campylobacter.
It said the overall increase in contamination from the first quarter was most likely due to the second quarter's samples being taken during the summer months, when an increase in campylobacter was often seen because of the warmer weather.
The 12-month survey, running from February 2014 to February 2015, will test 4,000 samples of whole chickens bought from UK retail outlets and smaller independent stores and butchers.
Campylobacter is killed by thorough cooking and can be limited by careful hygiene but it is the most common form of food poisoning in the UK, affecting an estimated 280,000 people a year.
Poultry is the source of the majority of these cases.
FSA director of policy Steve Wearne said: "These results show that the food industry, especially retailers, need to do more to reduce the amount of campylobacter on fresh chickens.
"Although we are only halfway through the survey, 18 per cent of birds tested had campylobacter over 1000 cfu/g, the highest level of contamination, and more than 70 per cent of birds had some campylobacter on them.
"This shows there is a long way to go before consumers are protected from this bug.
"If chicken is cooked thoroughly and preparation guidelines are properly followed, the risk to the public is extremely low.
"There are signs that some retailers are starting to step up to their responsibilities. When more do, we will see the sustained improvements that will help prevent many of their customers getting ill."
Retailers have rushed to announce measures to limit the bug in recent weeks, with the Co-operative and M&S introducing "roast in the bag" chickens to minimise handling at home.
Asda and its supplier Faccenda said they had committed to full-scale trials of new steam technology, although the FSA said any recent interventions would not yet be reflected in the survey results.
Additional reporting by PAReuse content