Pasteurizing Eggs in the Shell: Researchers Take Strides Against Salmonella

SEALED AND DELIVERED: Pasteurized Eggs has won USDA's first seal certifying the efficacy of the process for making eggs nearly Salmonella-free. The difference between pasteurized and unpasteurized eggs from the shell is hardly visible. The pasteurized ones (top) are slightly cloudier. Eggs, sunny-side up, have been on the path to becoming a relic of the past. Salmonella enteritidis (SE) has become one of the most common causes of bacterial foodborne illness in humans in the United States, and undercooked eggs contaminated with SE have been implicated as a primary mode of infection, according to the Centers for Disease Control and Prevention. Some large restaurant chains no longer offer sunny-side up eggs to customers, and many institutions such as hospitals and nursing homes use only pasteurized egg products already removed from the shell. But if L. John Davidson, president of Pasteurized Eggs L.P. in Laconia, N.H., has his way, shells will crack and yolks will run in kitchens around the nation. Pasteurized Eggs in June debuted its new process for pasteurizing shell eggs in Lancaster, Pa., the heart of the state's giant egg producing and processing industry. In partnership with Lancaster-based Food Processing Systems Inc. (FPS), the world's largest manufacturer of egg processing equipment, Pasteurized Eggs showed off to producers and processors from around the world its new mechanism for pasteurizing shell eggs. The machine itself is a marvel of engineering know-how and patience. After about three hours of tinkering and tweaking to assure that the demonstration would proceed without flaw, FPS unveiled the equipment to the public. Standing two stories tall and exceeding the length of a truck trailer, "Big Pete," as Davidson calls the machine, went on line. Eggs arrive for pasteurization via conveyer. After careful weighing of the eggs, a computer directs them to successive baths in water ranging from 62š Centigrade to 72š Centigrade. The actual temperatures and times of the baths are closely guarded company secrets. Davidson says the key to the process is allowing the heat to slowly penetrate to the center of the egg. While the pasteurization of eggs taken from the shell is commonplace, technical difficulties have stymied past efforts to pasteurize eggs still in the shell. "Pasteurizing the white part of the egg is easy," Davidson explains. "The trick is to get the center of the yolk to the same temperature without hard-boiling the egg. As anyone who has cooked an egg knows, the albumin, or white part of the egg, is especially sensitive to heat due to its density and chemical composition." The machine, which will be produced in the Lancaster machine shops of FPS, will cost egg processors about $1.5 million and add two cents to the wholesale cost of an egg. But Michael C. Clay, president of FPS, says the equipment will quickly pay for itself. "This is a highly effective machine designed to work on an industrial scale," Clay says. "At a thousand eggs per minute, you can pasteurize about 15 million eggs per shift each year." Prior to development of this process by Pasteurized Eggs, the U.S. Food and Drug Administration had set no standard for the pasteurization of eggs. That changed in 1994 when Davidson and the company asked FDA to set such a standard for shell eggs. In 1995, FDA then confirmed claims of pasteurization for the process by Pasteurized Eggs. By September 1997, the U.S. Department of Agriculture (USDA) agreed to issue a new stamp certifying that eggs undergoing the process met FDA standards. To date, Davidson's is the only company that can advertise its shell eggs as pasteurized. Davidson, of course, is hopeful that pasteurization can become an industrywide standard. "Right now, pasteurized eggs are a novelty," he says. "But in the near future, I think consumers will come to expect it just like they expect it of milk products." He notes that the market potential for pasteurized shell eggs is huge. In the U.S., the total market for eggs is estimated at about $6 billion annually, and only about 30 percent of all egg products are pasteurized. LEADING CAMPAIGN: Karen Davis, president of United Poultry Concerns, is leading a campaign to get the practice of induced molting outlawed in the U.S. The new process from Pasteurized Eggs comes at a time when eggs have drawn increasing attention as a health threat when improperly handled or cooked. USDA researchers in June issued a safety assessment of eggs to help policymakers estimate the scope of the problem and implement interventions. Using available data, a team of researchers in the Food Safety and Inspection Service (FSIS) of USDA estimated that 2.3 million of 46.8 billion shell eggs produced each year in the U.S. are infected with SE. The report also concludes that about 883,000 cases of human illness are caused by SE. Of these, 94 percent recover without medical care and 0.05 percent end in death. "As the numbers show, SE infection from eggs is a significant public health concern," says Arthur R. Baker Jr., an epidemiologist at FSIS. "About 5 percent of all eggs entering the food supply could be contaminated. So the potential for exposure to SE for a large portion of the population is great." The study relied in part on data on SE infection of spent laying hens to estimate risk of human illness. Spent hens no longer produce eggs and are typically sent to be slaughtered when they cease being productive. By collecting data on the rate of intestinal SE infection in these hens, FSIS researchers were able to estimate the carriage rate in living laying hens. While scientists are uncertain on how eggs ultimately become infected with SE , they have found that SE in the intestine significantly increases the risk of infection of the ovaries, according to Baker. "A laying hen with SE in the intestinal tract will not necessary have the same infection in ovaries and go on to produce infected eggs," Baker explains. "We do know that intestinal infections significantly increase the risk of producing infected eggs and this fact is incorporated in the model." Because technology for pasteurizing eggs was not available when the FSIS completed the risk analysis, Baker says there is no estimate of what effect it could have on human health. But he sees the technology as promising: "Pasteurization alone isn't going to eliminate the threat of SE in eggs. However, I can see it playing an important role in an arsenal of weapons for fighting Salmonella . Hopefully, Pasteurized Eggs would be willing to share their data on the efficacy of the process so that we could incorporate it into the model." Most scientists and policymakers on food safety agree that a multifaceted approach will be necessary to contain the threat of SE . Researchers in the life sciences can be expected to play a major role in this attack. Around the nation researchers, including Washington University (WU) veterinary immunologist J. Olu Hassan, are exploring new approaches to controlling SE infection. Hassan, along with WU professor of biology Roy Curtis III, is testing the safety and efficacy of an avirulent vaccine for Salmonella in chickens. Research on the vaccine began over 10 years ago when Curtis developed an avirulent strain of Salmonella. Hassan reports that trials for a vaccine using the avirulent bacteria have been highly effective. Hassan, along with WU professor of biology Roy Curtiss III, is currently testing the safety and efficacy of an avirulent vaccine for Salmonella in chickens. Research on the vaccine began over 10 years ago when Curtiss developed an avirulent strain of Salmonella. Experimental trials for a vaccine using the avirulent strain have been highly effective, Hassan reports. Most encouraging, he says that the vaccine prevents Salmonella colonization and shedding in vaccinated layers, thereby preventing the transmission of the bacteria into eggs. Vaccinated breeder hens also transfer maternal antibodies to chicks hatched from their eggs. Hassan believes that vaccination will become one of the most important strategies in Salmonella control. "But it won't be the only one," he says. "A comprehensive approach will include better public education on food safety, improved sanitary practices on the farm, [and] adequate Salmonella monitoring and surveillance measures. [All of these] are necessary to defeat Salmonella, a very prolific and ubiquitous organism." Another promising approach is under development at USDA's Southeast Poultry Research Laboratory in Athens, Ga. Microbiologists Peter Holt, Kun-Ho Seo, and Richard Gast are directing trials on the safety and efficacy of the antibiotic enrofloxacin and the competitive exclusion product Avigard from Bayer Corp. Holt says that while antibiotics are effective at killing Salmonella, they tend to worsen the situation by killing off nonpathogenic bacteria in the intestinal tract. In hopes of keeping Salmonella from taking hold after antibiotics use, Holt and Gast are testing Avigard, a so-called "competitive exclusion" product, which encourages the growth of harmless bacteria that crowd out pathogens like Salmonella in the intestinal tract. While use of the enrofloxacin/Avigard treatment is common in Europe, the combination has not yet been approved in the U.S. Holt says early trials completed this spring for the combination treatment have had striking success. In chickens receiving only antibiotics, the SE reinfection rate was about 25 percent. In chickens receiving antibiotics and the competitive exclusion therapy, reinfection was only at about 4 percent. "These results are very encouraging, Holt says. "Antibiotics alone sometimes exacerbate SE infection in birds and you have to worry because SE that survives this treatment may be drug-resistant. Competitive exclusion dramatically enhances the efficacy of antibiotics." Holt became interested in finding more effective strategies against SE when he was doing research on the effect of molting on the chicken's immune system. In that research, he found that "induced molting" raised the risk of SE infection in chickens and raised bacteria counts in those already infected. Induced molting is a common but controversial practice among egg producers in the U.S. Farmers, observing declining egg production in flocks, stop feeding chickens to produce weight loss and force molting. When feeding is resumed after a certain period, high egg production usually resumes. Activists such as Karen Davis, president of United Poultry Concerns, have taken a strong view of the research and say that the connection between Salmonella infection and induced molting ought to prompt egg producers to abandon the practice. Davis says the practice of induced molting is really forced starvation of laying hens and serves only the economic interests of producers. "Research has shown that Salmonella infection and forced molting are linked," Davis says. "This fact is concerning, but the bottom line is that this practice is cruel to chickens. Hens are essentially starved, and many die because of this practice." According to guidelines on molting from feed companies, chickens are fasted for 12 days to achieve a body weight reduction of about 30 percent. If mortality during this period exceeds 0.5 percent per day for the flock, egg producers are advised to resume normal feeding. Davis says this practice, among others utilized in the egg and poultry industry, is inhumane. She is now leading a campaign urging FDA to outlaw the practice in the U.S. In some European nations, health concerns and public pressure have prompted policymakers to ban the practice of induced molting. In the USDA's Pennsylvania Pilot Program for risk management of SE in flocks, farmers have stopped inducing molting in chickens known to be infected with SE . But Holt says it is unlikely that research relating SE and induced molting will ultimately prompt U.S. egg producers to completely abandon the practice. "Egg producers face a difficult situation," he says. "Many view induced molting as essential for maximizing productivity of laying hens. SE infection, of course, has a cost and they will have to find a way to balance these economic interests."

Pasteurizing Eggs in the Shell: Researchers Take Strides Against Salmonella

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