EHJ January 2005, pages 24-26

The most common source zoonotic infections in humans is thought to be through the foodborne route. Nick Warburton looks at why ensuring tight biosecurity measures at the farm is vital in reducing foodborne pathogens entering the kitchen

All sectors in the food chain have an important part to play in preventing harmful micro-organisms from contaminating food. As the Food Standards Agency's strategic plan for 2005-2010 rightly acknowledges, local authorities are making a significant contribution towards its target of reducing the incidence of foodborne diseases by 20 per cent by April 2006.

But as the strategic plan, Putting consumers first, clearly spells out, consumers have the right to expect more, which is why part of the FSA's five-year strategy will focus on primary food production to reduce contamination at source. By taking firm measures at this very early stage in the food chain, major foodborne pathogens such as campylobacters, salmonellae and Verocytotoxin-producing Escherichia coli (VTEC) O157 should be reduced. These harmful zoonotic infections are recognised as being the most important pathogens in terms of a foodborne disease burden.

As part of its strategy, the FSA aims to work closely with the farming industry to achieve a 50 per cent reduction in the incidence of UK-produced chickens, which test positive for campylobacter at slaughter by 2010.

Two years ago, it produced a strategy for controlling campylobacter in chickens as a way to reduce the presence of the organism. Campylobacter is responsible for over 50,000 laboratory confirmed cases of illness a year, a large proportion of which are thought to be foodborne. It was estimated that in 2000, the organism accounted for 27 per cent of all cases of indigenous foodborne disease and there is strong evidence to suggest that the most significant food source is chicken.

"Campylobacter is the most common cause of food poisoning in the UK and chicken is a major source of this type of bacteria in the kitchen," confirms Dr Judith Hilton, head of the FSA's microbiological safety division. "So, reducing campylobacter in chickens will help to reduce the risk of food poisoning."

The chicken industry in the UK is huge. According to the Advisory Committee on the Microbiological Safety of Food's draft second report on campylobacter, published last May, more than a million tonnes of chicken meat is produced in the UK every year, 96 per cent of which is from intensive production systems (housed birds).

While there is still some uncertainty surrounding the extent of the association of poultry meat in human illness, the report says enough is known to prove that the meat plays a significant role in the causal chain of events that leads to human foodborne illness. The human infectious dose is thought to be quite low and a single chicken could potentially carry millions of human infectious doses of campylobacter, the report notes. What's more, a 2001 FSA survey of raw fresh and frozen chicken purchased at retail in the UK found 50 per cent of all the samples that were tested were contaminated with campylobacter.

It is for these reasons that the first three years of the FSA's campylobacter strategy will focus on a campaign to improve biosecurity on intensive chicken farms. The idea is that by ensuring all farms achieve an appropriate standard of biosecurity, the number of campylobacter positive flocks will be reduced. This will have a knock on effect - reducing the numbers of contaminated birds leaving the slaughterhouse and cutting the levels of campylobacter-related illness. In this respect, getting it right at the farm end is vital.

"Certainly with poultry and chickens, I think the view is that once it's in the slaughterhouse, there is actually very little you can do about it," explains Dr Linden Jack, FSA lead on new and emerging zoonoses. "You can fine tune it but the thing is to stop it going in there in the first place."

CIEH policy officer Jenny Morris agrees. "When contaminated chickens go through the mechanical slaughter process, the way the birds are gutted can disperse campylobacter throughout this stage of slaughter. This has the potential to contaminate birds that are not infected. One way of reducing the likelihood of this happening is to reduce the prevalence of campylobacter at the farm stage and that means ensuring biosecurity measures are firmly in place and are enforced."

In July 2002, the Department for the Environment, Food and Rural Affairs published a voluntary code of practice for the prevention and control of salmonella in chickens reared for meat on farm. While it was specifically aimed at salmonella, many of the biosecurity measures it promoted are considered to be general good practice and can be applied to control campylobacter.

"Biosecurity, by and large, applies to most diseases," says Doug Kempster, a policy officer in Defra's animal health and welfare division. "There's a whole range of diseases that proper biosecurity would seriously tackle. It could go from something relatively mild all the way up to foot and mouth disease. It's that effective."

While awareness of the Defra code is high among the farming industry, the FSA admits this has not always translated into practice. "At the moment, we know from the work we did on salmonella that at times the most basic biosecurity measures weren't in place on all farms," says Dr Jack.

Ensuring biosecurity measures are properly implemented and enforced is particularly important in the case of campylobacter because it is widespread in the environment and requires tighter controls than salmonella to exclude it from poultry houses. One of the most important risk factors for introducing the organism into the flock is human traffic.

As Tom Humphrey, professor of food safety in the school of clinical veterinary science at Bristol University, explains "the organism is very commonly found in the natural environment and is brought into the house by people going into the house. The most basic thing is for people to change their footwear. To have footwear dedicated to each house and to help that, to have a defined hygiene barrier that separates inside from outside."

In other words, installing hygiene barriers where farm workers and visitors step over a barrier and change from footwear worn outside the house to dedicated footwear and clothing that is kept on the inside of the barrier.

Bearing in mind that most farms will receive visits, and even if this is minimised to essential visitors such as farm staff and vets, making sure that biosecurity isn't breached poses a major challenge for the farming industry.

Hand washing is another basic biosecurity measure that should be adhered to but one that has not always been followed. When the FSA carried out research on various aspects of poultry production covering salmonella and campylobacter, it found that on some farms the broiler houses did not have hand-washing facilities. In other cases, people entering the house were not required to wash or sanitise their hands.

Another common area that causes problems is the movement of equipment between broiler houses. FSA research has shown, for instance, that it is quite common practice for farmers to move weighing scales between houses. Some farms also allow pets and livestock - both reservoirs of salmonella and campylobacter - to roam freely in areas surrounding the broiler house. This is problematic when faecal material finds its way onto equipment or footwear and is carried inside.

Prof Humphrey says that many of the measures are common sense precautions and points to evidence from Scandinavia, which shows that enforcing tight biosecurity measures does have a significant impact on reducing foodborne pathogens. "If you look at what the most successful interventions have been, it's people changing their clothing, changing their footwear and washing their hands before they go into see the birds," he says.

"There was a study done by the Veterinary Laboratory's Agency in the early 1990s where they looked at the impact of Scandinavian-type intervention measures in UK production," he continues. "And they found that if they observed the strict biosecurity that the farmers in Norway do, they could reduce flock infection levels by 67 per cent."

Mr Kempster agrees that enforcing strict measures is vital. "Sometimes it can be inconvenient because it means taking that little bit longer but the benefits of practising good biosecurity far outweigh any slight inconvenience."

In January 2004, the FSA launched a new campaign to promote biosecurity at chicken farms. Working with chicken farmers and other poultry-industry stakeholders, the agency produced a leaflet and poster to highlight the most important biosecurity measures. They have also run various technical workshops to get the message across.

Prof Humphrey believes that farmers are taking the message on board and that practices are changing. "It can work but it's difficult to sustain long term and it will require a change in attitudes," he admits. "But we are beginning to notice this. Certainly, we are starting to see a reduction in campylobacter in UK poultry flocks."

Pointing to surveillance that his department has carried out on campylobacter found in caeca (blind gut) in chicken flocks at slaughter in the southwest region of England, Prof Humphrey says figures show the infection rate is lower than 10 years ago.

On a national scale, Dr Hilton says the FSA has recently launched a small on-going surveillance survey looking at chickens for retail sale across the UK. While the agency hopes to use the survey to monitor progress towards meeting its 2010 target on campylobacter, she says the data isn't available yet to say what the current trend is.

"The problem with looking at trends is often that if you are too close to the time when the samples were taken, what you don't know is whether any change is a real trend," she says. "It takes time before you can really be sure what trends are real. We'll be looking at what the surveillance is telling us but will probably be quite cautious about interpreting it."

The FSA recognises that campylobacter poses its greatest challenge if it is to meet its target of reducing the incidence of foodborne disease by 20 per cent by April 2006. While it's too early to see if measures taken at the farm end have led to a substantial reduction in campylobacter entering the food chain, it appears that farmers are more aware of the problem and the need to ensure tough biosecurity measures are in place to reduce the burden entering the kitchen.