ONE in five supermarket chickens is contaminated with the food poisoning bacteria campylobacter, an investigation has found.
The study of chicken samples from nine supermarkets found 18pc were contaminated with campylobacter and 17pc were contaminated with listeria, with 4pc containing levels of the latter classed as "high".
Salmonella was present in 1.5pc of samples, the investigation by the Which? consumer group found.
The watchdog tested 192 samples of whole chickens and chicken portions - standard, free range and organic - from a number of retailers in the UK last month.
Retail outlets in Ireland were not tested but the UK survey included Tesco, Aldi, Lidl and Marks & Spencer, along with five others, Asda, The Co-operative, Morrisons, Sainsbury's and Waitrose.
Bacterial contamination was found in samples from each of the retailers.
Which? stressed that the study was a "snapshot" as it tested each retailer on two days in different locations, and was therefore unable to definitively conclude that chicken from one supermarket was better than that from another.
However, the results indicated an improvement on 2009 when it was found that 65pc of fresh chickens it tested were contaminated with campylobacter at the point of sale.
It said consumers could avoid the risk of food poisoning by practising good food hygiene and cooking chicken thoroughly.
The watchdog also repeated advice not to wash raw chicken as it could splash the bacteria onto the sink, worktops or nearby dishes, increasing the risk of cross-contamination.
Campylobacter is one of the most common causes of food poisoning. It is found mainly in poultry but also in red meat, unpasteurised milk and untreated water.
Listeriosis, the foodborne illness caused by listeria, is relatively rare but listeria causes more deaths from food poisoning than any other foodborne bugs.
Most people infected with listeria are hospitalised and approximately a third die.
Which? executive director Richard Lloyd said: "While the situation is improving, it is still unacceptable that one in five chickens we tested were found to be contaminated with campylobacter.
"We want to see the risk of contamination minimised at every stage of production."