Free-range and organic chickens are twice as likely as battery hens to be contaminated with food-poisoning bacteria, a government-funded study for the Food Standards Agency has found.
More than 99 per cent of organic flocks are infected with campylobacter – potentially serious food-borne bacteria – compared with 56 per cent of conventionally reared chickens. Out of 75 free-range flocks, 69 were infected.
The agency tried to play down the findings yesterday, saying they were preliminary. And the Soil Association, which certifies organic farmers, said there was no evidence that the campylobacter strains found in chickens could lead to food poisoning.
But the agency said chickens were a major source of campylobacter and the micro-organisms were an important cause of food-borne disease. "Poultry plays a significant part in exposing humans to campylobacter organisms and reducing the number of campylobacter positive chickens on retail sale is likely to be an important step in reducing human infections," it said.
Tom Humphrey, a professor of food safety at Bristol University, released details of the poultry survey at a scientific meeting on organic food organised by the agency. All the contaminated birds identified by the study were destined for human consumption.
The findings closely match the results of a similar survey in Denmark which showed that organic chickens were up to three times more likely to contain food-poisoning bacteria, undermining claims that organic food is safer than conventional produce. The Soil Association said the British and Danish studies had not tried to distinguish the strains of campylobacter that can cause food poisoning from those that were harmless. The agency said: "Our understanding of which types of campylobacter cause disease in humans is still developing and we will be funding work to address this. There is a considerable body of evidence implicating chicken as a source of campylobacter infection in people."
Free-range and organic chickens that are allowed to roam outdoors are possibly more likely to be exposed to outside sources of campylobacter. Good kitchen hygiene and thorough cooking of meat can significantly reduce the risk of human infection.
The Soil Association said: "Humans and chickens have large numbers of bacteria in their intestines most of which are not just harmful but beneficial. There are hundreds of strains of beneficial campylobacter and only a very small number can lead to food poisoning." The association said that even if organic chickens were contaminated with campylobacter, the bugs were unlikely to be resistant to the antibiotics used to treat serious campylobacter infection.
"This is because the routine use of the equivalent veterinary drugs is prohibited and the extensive approach tends to reduce the incidence of other diseases for which intensive farmers need to use antibiotics," it said.
The agency is developing a strategy for the reduction of campylobacter in poultry which is has promised to publish next year. It is already committed to cutting salmonella levels in chicken by half. The national average level for salmonella infection in poultry is about 6 per cent.