EVERY major retailer is falling short of targets aimed at reducing levels of a bug that causes food poisoning, with contamination of shop-bought chickens increasing significantly since August.

The Food Standards Agency said results from the first two quarters of its year-long survey of fresh chickens found 70 per cent tested positive for campylobacter, up from 59 per cent in August.

Almost a fifth of all chickens (18 per cent) sold in stores tested above the highest level of contamination and six per cent of packaging tested positive - up from four per cent in August.

The FSA also put a figure on retailers' contamination rates 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 per cent 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 that had a lower incidence of chicken contaminated with campylobacter at the highest level than the industry average. Asda was the only major retailer with a higher incidence.

However, the FSA said the results suggested that none of the retailers was achieving the joint industry end-of-production target for reducing campylobacter.

FSA director of policy Steve Wearne said: "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.

The British Poultry Council said the figures showed that all producers and retailers had campylobacter levels in the same range.