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AIM AT A MOVING TARGET: FOODBORNE INFECTIONS by Joan Stephenson, Ph.D. appearing in The Journal of the American Medical Association January 8, 1997
In the wake of recent sieges by foodborne microbes, including an eruption of Escherichia coli O157:H7 infection traced to gourmet apple juice and an outbreak of Cyclospora cayetanensis-related illness linked to Guatemalan raspberries, public health officials are circling the wagons against an evolving microbial army. These two outbreaks, and other epidemics of foodborne infections in recent years, have focused attention on a dramatic shift in the epidemiology of such diseases that began roughly 15 years ago. That shift, experts note, is manifested not only by the emergence of relatively new microbial threats to human health such as E.coli O157:H7 and C.cayentanensis, but also by the appearance of more familiar pathogens in foods previously regarded as "safe," such as orange juice and alfalfa sprouts. Scientists estimate, based on several studies conducted over the past 10 years, that foodborne pathogens sicken from 6.5 million to 81 million people and cause some 9000 deaths in the United States annually, Michael Friedman, MD, deputy commissioner for operations at the Food and Drug Administration (FDA) told a congressional subcommittee last year. Precise figures on the prevalence of foodborne infections are hard to come by because surveillance is sketchy. Although the Center for Disease Control and Prevention (CDC) oversees a national foodborne disease surveillance system, the local and state health agencies that are the first line of defense often lack the resources or expertise to investigate outbreaks adequately. Underreporting of foodborne illnesses is the rule rather than the exception for a variety of reasons. Many of those stricken lack access to medical attention or elect not to seek it, particularly for self-limiting episodes of illness; physicians aren’t required to report such infections to public health authorities and often don’t order the stool cultures needed to nail down a diagnosis; and many laboratories lack the ability to identify the microbial culprit. Whatever the actual numbers, public health experts agree on two points: the numbers of reported cases are but a fraction of the actual toll, and such outbreaks are likely to become increasingly frequent in the future. Good for the Heart, Hard on the Gut Several factors are behind the emergence of new foodborne illnesses and the involvement of foods previously considered safe, said Michael T. Osterholm, Ph.D., MPH, state epidemiologist and chief of the acute disease epidemiology section at the Minnesota Department of Health, Minneapolis. One key element, the movement away from a traditional meat-and-potatoes American diet to "heart-healthy" eating--increasing consumption of fruits, vegetables, and grains while cutting back on meats and fatty foods--has led to changes in both the kinds and sources of foods people are consuming. "The heart-healthy diet may be kind to the cardiovascular system but it’s hell on the digestive tract." Osterholm noted at the annual meeting of the Infectious Diseases Society of America, in New Orleans, LA. Increased demand by U.S. consumers for a variety of fresh produce year-round and the globalization of the food supply have meant that a greater proportion of fruits and vegetables are imported--along with exotic pathogens. Today, depending on the season, up to 70% of the fruits and vegetables consumed in the United States come from Mexico alone. The upshot is that a visit to developing countries isn’t needed to be stricken with foodborne "traveler’s diarrhea" because the produce does the traveling instead. "We say ‘boil it, peel it, or don’t eat it’ when you travel to any of these countries (and eat produce), but in many instances you’re consuming the same product here without knowing it," Osterholm said. Microbial Needles in Haystacks Today’s mass production of foods and a global market that can move products around the world overnight have important implications when foods with sporadic and low-level contamination are consumed by thousands of people living hundreds of miles or more from the source. The large numbers of people exposed to such foods mean that an attack rate of less than 5% can result in thousands of cases. "Humans have become the ultimate bioassay (for sporadic or low-level contamination of foods)," said Osterholm, noting that microbiologic tests to screen food products aren’t the answer to preventing outbreaks, "How do you find that one in a thousand product that’s contaminated at a level potentially as low as a few organisms per gram?" Experts say that increased consumption of organically grown, unprocessed foods produced without fertilizers, pesticides, or preservatives may also be contributing to the problem. "`Organic’ means a food is grown in animal manure," noted Robert V. Tauxe, MD, MPH, chief of the CDC’s foodborne and diarrheal diseases branch, at the 36th Interscience Conference on Antimicrobial Agents and Chemotherapy, also held in New Orleans. Studies have found that E.coli can survive in cow manure for 70 days and can multiply in foods grown with manure, unless heat or additives such as salt or preservatives are used to kill the microbes. But there are essentially no regulations related to the use of animal manure in agriculture, said Tauxe, who predicted that oversight of the problem will ultimately be instituted by some government agency. "We got rid of human waste in our food and water, and I think we’re going to have better control in the future of manure in our good and water," he said. Becoming Proactive Some steps are under way to help health agencies move beyond simply reacting to outbreaks after they occur. One pilot project, a collaborative effort between the US Department of Agriculture’s Food Safety and Inspection Service, FDA, CDC, and state and local health departments launched in 1995, involves a foodborne diseases surveillance network at five sentinel sites in Atlanta, parts of California, Connecticut, Minnesota, and Oregon. Data collected for the program at the five sites should help health officials get a more precise picture of the occurrence of sporadic cases of foodborne infections in the United States and learn how the pathogens involved are transmitted. Ultimately, public health officials hope the system will be expanded beyond the pilot phase. Whether this will happen, however, will depend on future funding from Congress. Surveillance is only part of the answer though, because it uncovers problems that already exist but doesn’t prevent them, Osterholm said. A better understanding of where the weak links in the system exist is needed along with the ability to find ways to minimize or eliminate those weaknesses. Spurred by the recent outbreak of E.coli O157:H7 infection traced to tainted apple juice, federal officials are considering requiring producers of fresh fruit and vegetable juices to pasteurize their products. Also being debated are methods of decontaminating fresh produce using chemical solutions and requiring that all food companies adopt rigorous quality control programs similar to those now specified only for meat and seafood producers. Such programs demand that food producers take steps to prevent contamination at every point from harvest to sale. Food irradiation is another preventive measure that should be adopted to address foodborne disease, Osterholm said. Although the use of irradiation to pasteurize food has been endorsed by a variety of organizations, including the American Medical Association, World Health Association, and Institute of Food Technologists, food producers and consumers have been reluctant to embrace irradiated foods. "The foodborne outbreaks we’ve been reading about are going to occur over and over again, and the best chance we have (to prevent them) is food irradiation," he said. "The fact that we haven’t made it a priority in this country absolutely amazes me."
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