Zero tolerance for salmonella raises questions

Differences in regulations regarding salmonella sampling techniques, reporting requirements and salmonella control measures all make zero-tolerance import requirements suspect.

Poultry companies in the U.S. are placed in a very difficult situation. They are required to use chemicals in processing plants to lower salmonella incidence rates to levels deemed acceptable by USDA-FSIS.

However, because they use chemicals, they cannot export to the EU. Moreover, they cannot use cost effective measures to control salmonella during grow-out because they are against the law due to FDA regulations. Even though U.S. broiler processors effectively lower the salmonella incidence rate to 7.5% nationwide on post-chill carcasses, this is not acceptable to countries that have a zero-tolerance regulation in salmonella for imported poultry. To add to the difficulty, now the companies that are in Category 2 or 3 of the salmonella performance standard must have their data posted on the Internet, which eliminates their exports to zero-tolerance countries.

To understand how the U.S. poultry industry got into this Catch-22 situation you have to look at how salmonella control strategies have evolved differently in the U.S., Europe and the rest of the world. Additionally, the methods used to test poultry products for the presence of salmonella vary greatly from nation to nation.

Live production differences

In the U.S., regulations limit the types of interventions poultry companies may use to control salmonella during the processes of breeding, hatching, and grow-out. The reasons for these limitations are many, including: economic and environmental factors, regulatory agency restrictions and the massive scale of production.

In Europe, consumers are much less open to the use of chemical intervention during processing. As such, no chemicals are approved for use in poultry processing facilities in Europe. Therefore, a great deal of emphasis is placed on interventions during breeding, hatching, and grow-out. Some European countries test all breeder flocks for salmonella and, if a flock is found to be positive for salmonella, the company destroys the entire breeder flock. Most studies show that, using this extreme measure, these countries have been able to significantly reduce salmonella incidence rates to between 3-6% on birds coming into the processing facility.

Competitive exclusion

Another approach used in some EU countries successfully for many years is known as competitive exclusion. In Europe, adult chickens that are found to be free of salmonella are thought to have a competitive bacterial flora in their intestines which prevent colonization of the chicken with salmonella. These chickens are euthanized, and their intestinal tracts are removed. The lining of the intestines are scraped into a container and the bacteria are then grown to very high numbers. This solution is then sprayed onto the baby chicks to allow for colonization of their intestines with "good bacteria." This approach is known as undefined CE (because the bacteria in the mixture have not been identified and are unknown).

Use of undefined CE is illegal in the U.S. because the U.S. Food and Drug Administration requires that all bacteria fed to baby chicks must be identified and characterized to ensure that none of them are pathogenic and none of them are antibiotic-resistant.


The main approach in the U.S. to reduce salmonella during grow-out involves the use of vaccines. The vaccines are variable in terms of their efficacy because there are greater than 2,500 serotypes of salmonella and vaccines cannot be made to prevent all of them. There are five to seven main serotypes of salmonella that are commonly isolated from poultry carcasses in the U.S. The top five, in order of importance, are: 1) S. kentucky, 2) S. enteritidis, 3) S. heidelberg, 4) S. typhimurium (var. Copenhagen), and 5) S. typhimurium (USDA-FSIS, 2007).

In the EU, the serotypes of most concern are: 1) S. enteritidis, 2) S. typhimurium, 3) S. hadar, 4) S. infantis, and 5) S. virchow. Companies are doing a much better job of making the vaccines effective against a broad variety of serotypes. Even when using these vaccines, reductions of only 50% in salmonella prevalence on incoming broilers is common. Thus, additional measures in the field must be taken to lower salmonella further.

Drinking water acidification

A salmonella control measure employed by some companies is use of an acid or acid blend to watering systems during the feed withdrawal phase before slaughter. This disinfects the crops of the birds and lowers salmonella numbers in the crops during the feed withdrawal period. Because of the limited effectiveness of some on-farm salmonella control measures and the restriction on use of undefined CE, most emphasis on salmonella control in the U.S. has been placed on the slaughter operation.

Processing control differences

The USDA-FSIS views salmonella on poultry as a food safety issue and regulates the prevalence of salmonella that is allowable on poultry carcasses. However, the EU does not view salmonella as a food safety issue, but as a sanitation indicator. In the U.S., broiler carcasses are sampled at the end of the chiller by USDA-FSIS and the samples are evaluated for salmonella. If samples are in excess of the Salmonella Performance Standard (13 positive carcasses out of 51), then the USDA penalizes the plant. If this occurs three times, inspection is withdrawn and the plant is shut down. However, in Europe, no such regulations exist.

In the U.S., over 99% of companies use water-immersion chilling systems. In Europe, air chilling is most commonly used. This is important because a properly run immersion chiller is the most effective intervention tool available for poultry processors. Many companies in the U.S. are able to maintain salmonella at very low levels on carcasses using the chiller as the main intervention strategy. In Europe, no chemicals are used to reduce salmonella during processing, not even chlorine. This begs the question: In Europe, what happens when a flock that is contaminated with salmonella enters the plant or what happens when the interventions used in the field break down? Nothing is done.

Sampling differences

The way that poultry is sampled and tested varies greatly depending on the country where the tests are done. In the U.S., the USDA-FSIS inspectors rinse a chicken with 400 milliters of sterile buffered peptone water (whole carcass rinse). However, in the EU, plant employees collect a 25-gram neck skin sample from three different carcasses and pool them. Researchers conducted a study to determine which method is most sensitive for detecting the presence of salmonella on carcasses. Their research demonstrates that both methods are fairly equivalent for detecting salmonella but that neither is sensitive enough to be considered perfect. For example, on many carcasses, the neck skin method picked up the salmonella, but none was found in the carcass rinse for that carcass. In other cases, the reverse occurred.

Based on this study, both methods would need to be used together to really get a good idea of actual prevalence. It is important to note that in some countries around the world, in particular for exported product, the test method used is completely different than the two methods used regularly in the U.S. and EU. The chicken skin is sterilized using a blow-torch or iodine solution, then the skin is removed using sterile tweezers and a sample of deep breast muscle is taken and tested for salmonella. Amazingly, salmonella is never found using this technique, allowing the company/country to boldly state that they do not have any salmonella on their poultry. This is misleading and causes great confusion. By this testing method, a company could say that their chicken is sterile, which is of course, ridiculous. Meanwhile, the USDA-FSIS is forcing companies in the U.S. to post their salmonella prevalence, and their names, addresses and P-numbers on the Internet for the world to see.

Whose chicken is safer?

An extremely important question that must be answered is, what are the Europeans getting for the incredible expenditure on effort and money trying to eliminate salmonella from the breeder, hatchery and grow-out operations? In 2007, Sweden's rate of human salmonellosis was 42.8 cases per 100,000 of population and the rate was 14.9 per 100,000 people in the U.S. that year. Sweden is a country where breeders are euthanized if they have salmonella.

There should be an effort by leaders of all countries to use sound scientific principles to come together and agree on compatible methods for eliminating and testing for salmonella. There is no logical reason why a method like undefined CE, used in the field for many years in Europe to eliminate salmonella from the flocks without any adverse effects, cannot be used in the U.S. This causes great confusion for companies that operate globally and for consumers who believe they are buying "salmonella-free" chicken.

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