Salmonella – a serious threat from farm to fork

By DuPont Qualicon

Although the number of reported cases of salmonellosis in the European Union (EU) continues to decline, it still remains the second most common foodborne illness. According to the European Food Safety Authority (EFSA), approximately 35 out of every 100,000 EU residents was affected by salmonellosis in 2006, with the majority of these cases being attributed to the consumption of eggs, poultry or pork. Reducing the risk from salmonella is critical and requires action at every step of the food chain – from farm to fork. This article will provide an overview of the baseline surveys that were conducted to assist the European Commission (EC) in setting reduction targets for salmonella and will present information about a genetic-based system that detects Salmonella in food as effectively as traditional culture methods, but with quicker time to result.

What is salmonellosis?
Salmonellosis is an infection caused by salmonella bacteria. It is characterized as a zoonose, which means that it is an infectious disease transmitted from animals to humans, either through direct contact or from consumption of foodstuffs. There are many different kinds of salmonella bacteria, but the two serovars most frequently associated with human illness are Salmonella ser. Enteritidis and Salmonella ser. Typhimurium. In fact, S. Enteritidis causes more than 50% of the cases of salmonellosis in the EU.

Symptoms of salmonellosis typically include diarrhea, fever and abdominal cramps. Most people recover fully within four to seven days. However, it is possible in some cases for the infection to spread from the intestines to the bloodstream and then to other organs, resulting in death if the patient is not treated promptly with antibiotics. Those most at risk for severe illness and possible death from salmonellosis include infants, the elderly and those with compromised immune systems.

In the EU, most cases of salmonellosis can be attributed to the consumption of contaminated eggs, poultry or pork; however, any food, including vegetables, herbs and spices, can cause salmonellosis. Thorough cooking kills salmonella and proper food handling and good hygiene practices help prevent the spread of contamination.

Series of baseline surveys well underway
Recognizing the serious threat of salmonellosis and its implications for public health, legislators in the EC determined that reduction targets for salmonella must be set for EU farm animals. To provide the scientific basis for setting these targets, the EFSA is conducting a series of baseline surveys at the European Community level to determine the prevalence of salmonella in various farm animal populations. To date, four studies have been completed and the reports have been published.

The first survey was conducted in 2004 and 2005 on commercial large-scale laying hen holdings (at least 1,000 laying hens per holding) in all the Member States. Norway also participated in the study on a voluntary basis. The prevalence of salmonella varied greatly in specific Member States, but overall, salmonella was detected in 30.8% of the 5,310 holdings included in this study. In addition, more than 20% of the laying hen holdings tested positive for S. Enteritidis/S. Typhimurium. These findings were somewhat surprising because they were greater than those predicted by existing routine surveillance methods.

A second survey conducted in 2005 and 2006 on broiler meat flocks across the EU found nearly 25% of all flocks in the study to be positive for salmonella. Of the positive flocks, S. Enteritidis and S. Typhimurium were detected in approximately 40%. As was true in the first survey on laying hen holdings, the detection levels varied significantly between Member States.

The third survey was conducted in 2006 and 2007 on commercial turkey farms across the EU and in Norway with holdings of at least 500 birds reared for human consumption and at least 250 birds kept for breeding purposes. More than 30% of the turkey flocks reared for human consumption and nearly 14% of the turkey flocks kept for breeding purposes were found to carry salmonella. The percentage of flocks testing positive for S. Enteritidis and S. Typhimurium were relatively low, with 3.8% of flocks reared for human consumption and 1.7% of breeding flocks. Once again, the detection levels varied significantly between Member States.

A fourth survey conducted in 2006 and 2007 found that 10.3% of pigs in the EU slaughtered for human consumption were positive for salmonella. S. Typhimurium and Salmonella ser. Derby, two of the most common serovars in human infection, were detected in 4.7% and 2.1% of the herds. There was significant variance among Member States, and only one country reported no salmonella at all.

Later this year, EFSA will publish other baseline surveys on salmonella and campylobacter.

Implications of the baseline surveys
According to the baseline surveys published to date, salmonella was detected in nearly one out of every three laying hens, one out of every four broiler hens, one out of every three turkeys, and one out of every ten pigs intended for human consumption in the EU. This high prevalence, which in some cases surpasses the anticipated levels based on existing surveillance methods, has clear implications for the continued high risk of salmonellosis in the EU. In addition to serving as a valuable warning, this information also provides the necessary scientific data to enable the EC to set target reduction levels, especially for the two most common serovars, S. Enteritidis and S. Typhimurium.

In an effort to reduce the incidence of foodborne illnesses in the EU, the European Parliament and the Council of 17 November 2003 issued Regulation (EC) 2160/2003 for the control of salmonella and other specified foodborne zoonotic agents. Armed with the results of the EFSA baseline surveys, the EC is expected to set EU-wide reduction targets for S. Enteritidis and S. Typhimurium for a transitional three-year period.

Although other serovars are not currently slated for inclusion in Regulation (EC) 2160/2003, the EFSA’s Zoonoses Task Force is recommending that Member States also take action within their national control programs against other types of salmonella that are prevalent in their countries.

Between the farm and the fork
The reduction targets for S. Enteritidis and S. Typhimurium that the EC sets will be a challenge for many of the Member States that have high contamination levels. And, even with successful reduction of salmonella levels at the farm, the potential for disease-causing bacteria to be spread at a food processing/manufacturing facility is still a real threat.

Food processors/manufacturers play a crucial role in food safety between the farm and the fork, serving as a critical gatekeeper. So, despite reduction targets for farm animals, the need for vigilance in detecting the presence of salmonella in raw ingredients, finished products and the processing/manufacturing environment is as important as ever.

One concern often voiced by food processors/manufacturers is the long delay to get results from a traditional culture-based testing method. Waiting up to four days to make release decisions can mean the difference between profit and loss, especially with today’s growing demand for products with fewer preservatives.

Fortunately, food processors/manufacturers now have alternatives. For example, the BAX® detection system from DuPont Qualicon provides the food industry with a next-day method for detecting salmonella. The use of automated polymerase chain reaction (PCR) processing with tableted rather than liquid reagents creates a dramatic increase in speed.

Extensively validated, the BAX® system is used around the world for food safety testing and has been certified by AOAC International, AFNOR and NordVal. Government agencies in Canada, Brazil and China have also approved this method, and the USDA Food Safety & Inspection Service uses the BAX® system to monitor meat and poultry in the US.

Conclusion
Based on the data collected from the baseline surveys, it is clear that salmonella will continue to pose a serious threat for the foreseeable future. Setting reduction targets for the two serovars most commonly associated with salmonellosis is an important part of protecting the health of EU residents. However, this measure will not eliminate the existence of this disease-causing bacteria, nor will it reduce the need for food processors/manufacturers to test for the presence of salmonella in their operations.

The BAX® system from DuPont Qualicon can help food processors/manufacturers get accurate, reliable results much faster than possible with traditional culture methods. This will not only improve the overall safety of the food supply, it will also help food companies protect their brand images and improve their bottom lines.