Data shows thousands of fresh supermarket chickens are contaminated with a potentially lethal food poisoning virus.

Up to one in 25 raw roast chickens sold in the UK are classed as highly contaminated with Campylobacter, the leading cause of food poisoning.

The Food Standards Agency (FSA) orders supermarkets to measure levels of the bacteria and sets strict targets on the proportion of poultry meat that can be affected.

None exceeded the agency’s limit. But at the worst-performing supermarkets – Asda, Lidl and Waitrose – up to four per cent of raw chickens on their shelves carried the virus.

Campylobacter usually causes diarrhea, nausea and vomiting that improves on its own within a week. But in severe cases it can kill vulnerable groups, including young children, the elderly and immunocompromised.

The Food Standards Agency (FSA) orders supermarkets to measure levels of the bacteria and sets strict targets on the proportion of poultry meat that can be affected. None exceeded the agency’s limit. But at the worst-performing supermarkets – Asda, Lidl and Waitrose – up to four per cent of raw chickens on their shelves carried the virus.

Supermarkets must report data on the prevalence of Campylobacter among their poultry products every three months so that the FSA can monitor food quality.

They share the proportion of their raw roast chickens that have more than 1,000 colony-forming units per gram (CFU/g) of Campylobacter. At this level, chickens are considered highly contaminated and carry a risk of food poisoning.

Retailers are supposed to ensure that no more than seven percent of their chickens exceed these levels.

Data from 2023 shows that no supermarket exceeded seven percent.

However, Asda recorded the highest average level compared to other retailers.

WHAT IS CAMPYLOBACTER?

Campylobacter is the most common cause of food poisoning in the UK.

About four in five cases of Campylobacter food poisoning in the UK come from contaminated poultry, especially chicken.

One of the main ways to get and spread Campylobacter poisoning is through cross-contamination during food preparation. For example, if you wash raw chicken, Campylobacter can spread to work surfaces or hands.

But the bacteria is still found in red meat, unpasteurized milk and untreated water.

Most people who become ill from Campylobacter recover completely. But it can cause serious, long-term health problems in some people.

It is estimated that approximately one in every 1,000 reported cases of campylobacteriosis leads to Guillain-Barré syndrome.

Deaths are rare in the developing world. Children under five and older people are most at risk because they may have weaker immune systems.

Symptoms of infections include diarrhea, which may be bloody, abdominal pain, fever, headache, nausea and vomiting. Symptoms usually last three to six days.

How can you avoid Campylobacter poisoning?

You can help keep your family safe from Campylobacter by chilling your food, cooking chicken properly, avoiding cross-contamination, and ensuring good personal hygiene.

You can avoid cross-contamination by never washing chicken or letting raw chicken come into contact with ready-to-eat foods.

The data show that 3.6 percent of their samples had more than 1,000 colony-forming units per gram (CFU/g) of campylobacter from January to March.

The supermarket registered a level of 3.52 percent between April and June, which gives it an average of 3.4 percent in the first half of the year.

By comparison, it recorded rates of 6.1 and 6.9 percent in 2017 and 2018, just below the safe threshold.

In 2022, however, only 1.1 per cent of all Asda chicken tested throughout the year contained more than 1,000 CFU/g.

Meanwhile, Lidl said it recorded levels of “almost four per cent”, suggesting it was among the highest rates in the first quarter of the year.

However, in the second and third quarters, this figure fell to “almost two percent,” he said.

“Our poultry suppliers are working hard to increase biosecurity on farms to reduce campylobacter in poultry,” Lidl said.

“Our poultry suppliers have implemented innovative interventions in factories to reduce campylobacter during the slaughter and production process.”

Waitrose, similarly, recorded a rate of 4.04 per cent in the first quarter, which fell to two per cent in the second quarter.

The figure is higher than last year, when just 1.28 per cent of all Waitrose raw chickens tested contained more than 1,000 CFU/g.

A spokesperson for the supermarket told MailOnline: “These results reflect the hard work of our farmers and suppliers combined with our own rigorous data collection and analysis, examining chicken both in the factory and on supermarket shelves.”

During the first quarter of the year, supermarkets Sainsbury’s and Marks and Spencer posted results of three per cent and less than one per cent respectively.

This fell to one percent and zero in the second quarter for each retailer respectively.

A Sainsbury’s spokesperson said: ‘Safety is our top priority. We are committed to combating campylobacter in chicken and our regular testing shows that levels remain within the Food Standards Agency’s recommendations.’

Meanwhile, Morrisons recorded a level of 2.4 per cent from a sample of 84 chickens tested in the first quarter of 2022 and 2.3 per cent from 86 chickens in the second quarter.

Morrisons has not exceeded the seven per cent safety limit since 2014.

Until July, the Cooperative had not seen a single sample contaminated with levels greater than 1,000 CFU/g since the third quarter of 2021.

But between July and September, 3.5 percent of respondents met the threshold.

A spokesperson for the Co-op told MailOnline: “Food safety is a priority and as a responsible retailer we have carried out our own Campylobacter tests to accompany those of the FSA.

“In line with our commitment to transparency, we have published our results and are pleased that the third quarter 2023 results are well below the FSA’s maximum target level.”

Supermarkets must report data on the prevalence of Campylobacter among their poultry products every three months so that the FSA can monitor food quality. They share the proportion of their raw roast chickens that have more than 1,000 colony-forming units per gram (CFU/g) of Campylobacter. At this level, chickens are considered highly contaminated and carry a risk of food poisoning. Retailers are supposed to ensure that no more than seven percent of their chickens exceed these levels.

Tesco stopped publishing data because it changed the way it monitors the pathogen in chicken, so the findings are not comparable with those of other retailers.

Aldi has not updated its related website or provided figures to MailOnline.

Campylobacter is responsible for approximately 50,000 cases of illness in England each year and is one of the four leading causes of diarrhea in the world.

More worrying is the fact that some strains of the bacteria have mutated to develop resistance to antibiotics used by doctors to treat serious illnesses.

The latest statistics show that the average Brit consumes 35kg of poultry every year.

Apart from the misery and pain of the disease itself, the FSA estimates that the bacteria costs the economy around £900 million a year in terms of NHS treatment and days lost at work.

To avoid food poisoning, people should make sure they cook chicken thoroughly, separate the meat from other foods, store it in the refrigerator, and wash their hands and utensils after handling raw meat, according to the FSA.

Chicken should also not be washed because it can spread bacteria to other parts of the kitchen, he added.