The Changing Nature of Food Hazards: Cause for Increasing Concern
There have been dramatic changes in the US food supply. These changes have contributed to recent outbreaks of infectious foodborne illness, which in turn led to the request for this committee to examine aspects of the US food safety system. The committee recognizes the growing concern for controlling the microbiological hazards related to food, but believes that government attention must also be addressed to chemical and physical hazards. This chapter is organized in two parts: the first describes major changes that affect the epidemiology of infectious foodborne disease, and the second describes examples of potential chemical hazards which have emerged in part from some of the same changes in the food supply. Physical hazards related to food are addressed briefly at the end of this chapter.
CHANGES THAT AFFECT THE EPIDEMIOLOGY OF FOODBORNE DISEASE
Recent outbreaks of foodborne disease caused by many different pathogens and involving a variety of food products have been the subject of headlines, but it is unclear whether the incidence of foodborne disease has increased over the last generation. The major reason for the uncertainty is that the lack of a national foodborne-disease surveillance system has prevented the study of trends in disease rates. What is clear is that factors affecting the potential safety of the nation's food supply have changed dramatically over the last generation and
justify concern that the incidence of foodborne disease is high and may be increasing.
At least five trends contribute to the possible increase in foodborne disease: changes in diet, the increasing use of commercial food services, new methods of producing and distributing food, new or re-emerging infectious foodborne agents, and the growing number of people at high risk for severe or fatal foodborne diseases.
Annual food expenditures in the United States, as a share of disposable personal income, decreased from 14 percent to 11 percent from 1970 to 1996 (Putnam and Allshouse, 1997). No industrialized nation spends a smaller share of its wealth on food than the United States. For much of the population, readily available food is more varied and more affordable than ever before. For example, in the 1960s, an average US grocery store had fewer than 7,000 food items available. Today, an average US grocery store sells about 30,000 food items (FMI, 1997b), and over 12,000 new products are introduced each year (New Product News, 1998).
During this time when relative costs of the US food supply are decreasing, per capita consumption of many foods has changed substantially. Public health efforts to promote a ''heart-healthy" diet have helped to boost the consumption of fresh fruits and vegetables. On a per capita basis, in 1995, Americans ate about 31 lb more commercially grown vegetables, including potatoes and sweet potatoes, and 24 lb more fresh fruit than in 1970 (Putnam and Allshouse, 1997). As the consumption and variety of produce have increased, so has the importation of produce from developing countries. The General Accounting Office estimates that in 1995 one-third of all fresh fruit consumed in the United States was imported (GAO, 1998). Food imports have increased both because of lower production costs in foreign countries and because of consumer demand for year-round supplies of fruits and vegetables that have limited growing seasons in the United States. For example, 17 percent of cantaloupes, 52 percent of green onions, 36 percent of cucumbers, and 34 percent of tomatoes sold in the United States in 1996 were grown in Mexico (Osterholm et al., 1998). Seasonally, as much as 79 percent of a particular commodity consumed in this country has been raised in Mexico alone, and the percentage of produce from other developing countries consumed here is growing rapidly. Fresh produce items were the leading vehicle associated with foodborne disease outbreaks in Minnesota from 1990 to 1996, accounting for almost one-third of all outbreaks (Osterholm et al., 1998). This percentage is higher than that available from national foodborne disease surveillance data and possibly reflects more active surveillance in that state.
Other trends in the United States are the decreasing consumption of beef and the increased consumption of chicken and seafood. In 1970, the average
American consumed 79 lb of beef, 27 lb of chicken, and 12 lb of fish and shellfish; in 1996, annual per capita consumptions were 64, 50 and 15 lb, respectively (Putnam and Allshouse, 1997). Contamination of red meat with Salmonella and Escherichia coli 0157:H7 remains important, but the risk posed by chicken as a vehicle for Campylobacter and Salmonella has grown substantially (Consumers Union, 1998).
Cultural changes affect not only what Americans eat, but also where they eat and how their food is prepared. Increasingly, Americans have time-pressured lifestyles. Saving time and effort in shopping for and preparing food will continue to be important for many Americans. Households with a single parent or two working adults often face particular pressures in food shopping and meal preparation that can affect food selection and safety (Federal Coordinating Council for Science, Engineering, and Technology, 1993). Cookbook sales and television cooking shows demonstrate that cooking is popular, but there seems to be decreased interest in ordinary daily home food preparation and, with most adults working, a lack of role models in the kitchen. Reductions in time for and interest in home food preparation also result in changed food patterns, fewer homemade dishes, more reliance on leftovers, increased purchase of prepared or convenience foods, and frequent eating away from home (FMI, 1997a).
With less time spent in the kitchen and greater availability of high-quality, ready-to-eat dishes and convenience items, Americans' food preparation skills are diminishing. As a result, appreciation of simple but critical food safety techniques, such as washing hands and utensils and storing foods at optimal temperatures, has likely diminished.
Individual food tastes and preparation styles are brought to the United States from around the world, and the increasing ethnic diversity of the American population may affect food safety in several ways. Different ethnic groups have different concerns and practices regarding food safety, and this could affect the activities of immigrants as food preparers at home and in the workplace. New food risks can arise as immigrant populations adapt traditional preferences and practices to their new environment. Food safety education programs should consider the food beliefs and practices of various cultural groups.
Although data show a rise in perceived risk of foodborne illness among consumers (Alan Levy, FDA, Food Safety Survey Data, communication to committee, June 1998), attitudes do not always translate into improved food-handling practices. Over half of all shoppers report washing their hands and/or food preparation surfaces, yet only 28 percent know that cooking temperatures are critical and that foods should be refrigerated promptly (FMI, 1998a). A recent Food and Drug Administration (FDA) study found that many US consumers still eat undercooked hamburger meat and raw eggs (Alan Levy, FDA, 1998 Food Safety Survey Data, communication to committee, June 1998).
Commercial Food Services
The percentage of the food dollar spent on food consumed away from home has risen dramatically over the last three decades. In 1970, only 34 percent of our food dollars were spent eating away from home. In contrast, in 1996, 46 percent of our food dollars were spent for meals and snacks prepared outside the home (Putnam and Allshouse, 1997). Institutional feeding sites serve a wide range of people—from very young children in child care centers to the elderly—in congregate sites for meals, alternative-care centers, and nursing homes. Meals are also prepared as takeout foods from supermarkets and convenience stores; many of these meals include one or more cold food items, such as delicatessen sandwiches and salads that require extensive food handling and are not cooked before consumption. These changes have led to an increase in the number of people handling food and the potential for an increase in the transmission of foodborne diseases from food handlers to consumers.
The average food handler in this country earns the minimum wage, lacks sick leave and other health benefits, and has very limited opportunities for advancement. These jobs are filled by people with few employment opportunities and low economic status, conditions that may be related to a high incidence of intestinal diseases and low rates of routine hand washing. Recent evidence from Minnesota demonstrates the increased risk of food handler associated transmission of Salmonella typhimurium; this finding was documented because Salmonella isolates in Minnesota undergo molecular characterization and epidemiologic investigation (Osterholm et al., 1998). Food handlers in other areas of the United States probably play a similar role in the transmission of Salmonella and other enteric agents.
Methods of Production and Distribution
The changing availability and sources of our food supply have brought changes in methods of producing and distributing food. Today, large manufacturing plants can process quantities and types of products that two decades ago would have required many smaller plants. Although the ability to control possible hazards increases when there are fewer plants, the potential for larger outbreaks—even if product contamination is minimal—is evident. Thousands of people become ill during such outbreaks. For example, contamination of tanker trucks with nonpasteurized liquid eggs and subsequent use of those trucks to haul pasteurized ice cream mix most likely led to the largest documented outbreak of salmonellosis in the United States (Hennessy et al., 1996). That outbreak showed that even sporadic low level contamination of a single product can result in a major epidemic of foodborne illness because of the quantity of product consumed.
In the spring of 1998, a cereal produced by the largest generic label manufacturer of cereal in the United States caused a national outbreak of Salmonella agona infection. Outbreaks such as this can be difficult to detect because contamination of the product is sporadic and the product is marketed widely.
The driving forces of globalization, advanced technology, and economic competitiveness have dramatically affected the structure and practices of livestock and poultry production. Herds, flocks, and other populations of food animals, including fish and seafood, are increasingly concentrated in fewer and larger production units. The traditional farmstead model of the past, often characterized by multiple species and small numbers of food animals reared on a single farm, has been replaced by specialized, large-scale production systems. For example, from 1994 to 1995, the number of US hog operations decreased from 207,980 to 182,700, but both the inventory of hogs and the total number of hogs produced increased during the same time (NASS, 1995). That mirrors the general agribusiness trend, and the restructuring continues.
New or Re-emerging Infectious Foodborne Agents
The role of new or re-emerging causes of foodborne diseases is well-recognized, but the size of the increase in risk is unknown. Emerging and reemerging infections have been defined as new, recurring, or drug-resistant infections whose incidence in humans has increased in the last two decades or whose incidence threatens to increase in the near future (NRC, 1993). Recent examples of newly recognized agents are E. coli 0157:H7, other pathogenic E. coli, Cyclospora, and Cryptosporidium. Old agents re-emerging in new vehicles or product streams include Salmonella enteritidis in eggs and hepatitis A virus in produce. Finally, there have been recent increases in antimicrobial resistance of pathogens, such as S. typhimurium DT104 and Campylobacter jejuni in humans, which have been attributed to the use of antimicrobial agents in food animals (Osterholm et al., 1998).
The frequently cited annual estimates of foodborne disease (up to 81 million cases) and 9,000 associated deaths are based on assumptions that do not necessarily reflect the current national foodborne disease problem. Those estimates must be qualified for two reasons. First, no comprehensive population-based studies of gastrointestinal illness in the community have attempted to determine what proportion of these illnesses is due to consumption of contaminated food and what proportion is from other sources. Second, foodborne illness can cause clinical conditions not characterized by gastrointestinal symptoms, such as congenital toxoplasmosis, hemolytic uremic syndrome, salmonella-associated septicemia, and invasive Listeria infections (Morris and Potter, 1997). In the absence of comprehensive estimates of foodborne disease incidence, the only data available are those from the FoodNet program.
Data from FoodNet-an effort sponsored by the Centers for Disease Control and Prevention, the US Department of Agriculture, FDA, and the health departments of California, Connecticut, Georgia, Minnesota, and Oregon-have demonstrated that the incidence of diarrheal illness in the United States is about 1.4 episodes per person per year, or some 370 million episodes of diarrhea each year. Population-based studies of diarrheal disease conducted from 1948 through 1971 in Ohio and Michigan demonstrate an incidence of about one episode per person per year (Osterholm et al., 1998). The reason for the apparent 40 percent difference between these estimates is unclear, but it is evident that the problem is large. If only 25 percent of diarrheal disease is food-related, the burden of foodborne diarrheal disease in the United States far exceeds current estimates.
Studies conducted by FoodNet suggest that fewer than 2 percent of the cases of diarrheal illness in the United States can be attributed to Salmonella, Campylobacter, Shigella, E. coli 0157:H7, and Yersinia (Osterholm et al., 1998). Little information is available on the role of other pathogens, including newly recognized agents such as Shiga toxin-producing E. coli other than 0157:H7, Cryptosporidium, and Cyclospora, and previously established pathogens such as Norwalk-like viruses, Clostridium perfringens, Staphylococcus aureus, Bacillus cereus, and hepatitis A virus. Until additional studies elucidate the role of the recognized pathogens in foodborne disease, we can only speculate about the occurrence of new or unrecognized pathogens.
Populations at High Risk for Severe or Fatal Foodborne Disease
The risk of foodborne disease is related to several factors, including the presence and dose of a pathogen or toxin in food, the virulence of the pathogen or toxin, the mechanisms of transmission, and the susceptibility of a host. Many factors influence susceptibility to infection and the severity of disease, including age, the use of immunosuppressive agents, and disease states that increase immunosuppression.
Young children are more likely than adults to develop illness from selected pathogens, and children have been high-profile victims of several foodborne disease outbreaks in recent years. Young children today are likely to be exposed to a broader range of foodborne diseases than was true a generation ago, because families eat out or take prepared food home more often and children receive more community and out-of-home care at younger ages.
Elderly persons are particularly susceptible to illness from foodborne disease, and the number of the elderly in the United States is increasing rapidly. From 1965 to 1995, the number of Americans aged 65 years or older grew by 82 percent. As the 75 million persons in the "baby boomer" generation (equaling one-third of the population) age, the United States can expect one fifth of the population to be over the age of 65 within the next three decades (US Census Bureau, 1997).
As the population ages, the incidence of cancer and other chronic diseases is likely to increase. These diseases will require an increased use of chemotherapeutic regimens, drugs to deal with rejection of solid organ transplantations, and antimicrobial drugs that have important effects on the normal (and beneficial) bacterial flora of the intestinal tract. Together, these factors predispose people to both the occurrence and the serious outcomes of foodborne disease. The increasing number of people with immunosuppressive diseases, such as human immunodeficiency virus, also contributes to the public health importance of food safety.
Changes in Chemical Hazards Associated with the Food Supply
Changes in our society and our food supply have raised new concerns about food chemical safety. Some of the changes that have raised new concerns about foodborne infectious disease are also affecting how government agencies carry out the more familiar task of protecting the food supply from toxic chemical agents.
Foods are themselves a complex collection of naturally occurring chemicals that have nutritive, organoleptic, and pharmacological functions and occasionally toxic effects. Naturally occurring toxicants probably present risks second only to those imposed by microorganisms. These natural toxicants include seafood toxins and foodborne mycotoxins.
Other chemicals are introduced into foods intentionally or unintentionally. Intentionally added substances include food and color additives, flavors, enzymes, vitamins and minerals, and other ingredients that help to add value or characteristic properties or functions to a food. Because of broad public concern about synthetic chemicals, the toxicologic profiles of many of these synthetic components of food are much more complete than those of natural components of food. As a result, the risks posed by regulated food additives are generally better characterized than those of many naturally occurring substances.
Unintentional additives can include environmental or industrial contaminants as well as some substances used in food production but not intended to be part of the food. The migration of food production substances into the final product is generally very low, but must be carefully regulated to ensure safety. Examples include sanitizers used to keep food production surfaces safe, packaging materials used to keep food safe and fresh, pesticides used on crops and drugs used in animals to mitigate damage, disease, microbial toxin production, and general food losses. Environmental or industrial contaminants are not sanctioned but have the potential to enter the food chain. Examples of chemical contamination incidents are methyl mercury in fish, mistaken mixing of polybrominated biphenyls (a fire retardant) into animal feed, and leakage of ammonia refrigerant into frozen foods.
Some people are sensitive or allergic to chemical constituents that are harmless to the rest of the population. These allergic reactions are estimated to occur in 1 to 2 percent of adults and 5 to 8 percent of children. Although serious reactions are rare, it is estimated that several dozen deaths occur each year because of allergic reactions to food (Bock, 1992). More than 160 foods and food-related substances have been identified as being able to cause allergic reactions (ILSI, 1996). However, in the United States, more than 90 percent of allergic reactions appear to be caused by just eight food types: peanuts, tree nuts (such as walnuts, pecans, almonds, hazel nuts), crustacea (shrimp, lobster, and other shellfish), eggs, milk, soy, fish, and wheat (Hefle et al., 1996).
Consequently, the subject of chemical hazards in food is complex and includes consideration of potential risks that vary widely in scope and severity. Many chemical hazards associated with foods have been recognized only in the last century as advancements have been made in chemistry, toxicology, and risk assessment. Public concern over these hazards has grown in recent decades, in line with the increasing distrust of chemicals generally and of their use in the environment. Indeed, there have been episodes of chemical intoxication (usually arising out of accident or occupational exposure) with tragic consequences. Although most experts agree that the more serious hazards in the American food supply are not chemical but microbiological, public concern has demanded that proportionally more regulatory resources be applied to chemical hazards (IFT, 1989).
New Food Components
The American public's growing interest in the relationship between diet and health has led to an increased demand for foods or food constituents that not only have nutritive value but also hold promise for prevention or even treatment of disease. These products have been referred to as dietary supplements, functional foods, pharma-foods or nutraceuticals. In a recent study, more than two-thirds of surveyed households reported use of a vitamin, mineral, or herbal supplement within the previous six-month period (Hartman and New Hope, 1998). The Dietary Supplement Health and Education Act of 1994 eased restrictions on certain statements of nutrition support made for supplements and exempted them from the safety approval requirement applicable to conventional food additives. That legal change helped spur the growing market for supplements of all types, including herbal products, and raises food safety concerns. Some supplements and herbal products on the market may pose a risk of adverse health effects because they are not required to meet specified safety standards before being sold. They may thus contain varying amounts or unknown or inadequately characterized ingredients that can have pharmacological activity that has not been adequately characterized (for example, ephedrine in Chinese ma huang).
Food processors are examining relatively new sources of ingredients for more conventional functional properties. For example, gums and fibers such as konjac flour, tara gum, inulin, or psyllium fiber may provide bulk and texture to foods, yet have had limited food use in the United States. Potential broad use of these ingredients in domestic foods raises important safety questions: are there significant intestinal effects such as blockage or reduced transit times? Are there impacts on vitamin uptake from the intestinal tract or on osmotic balance? What are the potential allergy risks from increased exposure to plant-sourced materials? These are a few of the safety questions that may be raised when a new ingredient source is considered.
Food processors are also utilizing macronutrient substitutes, such as nonnutritive sweeteners and fat replacers in many food products. These macronutrient substitutes have potential value by lowering calories, sugar, or fat in food products. Because dietary quantities of these substitutes could be substantially higher than the amounts of typical food additives, the assessment of their safety can be particularly important as well as particularly difficult.
New Food Technologies
Modification of plants or animals via genetic engineering can improve yields and increase resistance to pests. This new technology might offer improvements in food safety through increased resistance to molds that produce food mycotoxins or through lower levels of allergenic proteins, fatty acids, or other undesirable components of food. However, there are important differences between countries in how food products from genetically modified organisms are regulated. Several products derived from genetic engineering have been declared safe by US regulators, but many European countries have either forbidden their sale or insisted on what marketers believe is disparaging labeling. Concerns about the safety of products from genetically engineered plants and animals are only partially resolved.
Food irradiation is not a new technology. Irradiation of fruits and vegetables decreases the risk of pathogens and extends shelf life. But as discussed in Chapter two, public concerns about the safety of irradiated food, fueled in part by a lack of consumer education, limits its use in the United States (FMI, 1998b). These concerns prompted the requirement that certain irradiated foods be labeled as such. The extent to which this labeling requirement has limited subsequent adoption of the process is unknown.
New or Re-emerging Toxic Agents
As the science of toxicology has progressed over the last 50 years, questions about the safety of chemicals in foods have become more sophisticated. When tougher safety standards are applied to new food chemicals or reapplied to old ones, new issues of toxicity emerge. The cycle of re-
evaluating safety standards began in the years after World War II when advances in the understanding of the mechanisms of carcinogenesis coincided with the increased use of rodent bioassays. The newly focused attention to carcinogens that ensued led Congress to pass the 1958 "Delaney clause" proscription of carcinogens. The focus on carcinogens in food continues to consume substantial testing and regulatory resources. Further advances in biomedical research have raised new concerns and new standards of safety that now address teratogenicity, reproductive toxicity, mutagenicity, hormonal effects, and immunotoxicity.
The effects of food constituents on hormonal function is of concern as medical research has indicated the importance of certain hormones in regulating diseases such as breast cancer and osteoporosis. This phenomenon, sometimes referred to as endocrine disruption, led Congress in 1996 to mandate special regulatory attention to the issue and inspired the Environmental Protection Agency (EPA) to convene an expert panel, the Endocrine Disrupter Screening and Testing Advisory Committee. That committee has attempted to define endocrine disrupters, determine analytical methods, and recommend how the disrupters should be regulated. Potential candidates for evaluation include constituents of some food packaging materials, pesticides, and natural food constituents, such as genestein in soy.
Some groups have recently asked whether chemical safety assessments provide adequate safety margins to protect children (Guzelian et al., 1992; NRC, 1993). That concern draws attention because new pesticide legislation directs EPA to consider the aggregate risks posed by any pest control agent; that is, exposures should be assessed for all potential sources of a chemical and for other chemicals with a similar mechanism of action (21 USCA sec. 342(b)(2)(A)(ii)). Another concern is the emergence of evidence of subtle developmental and behavioral effects of relatively low concentrations of chemicals (for example, lead).
In summary, chemical hazards, as well as foodborne pathogens, present new and changing challenges to the food safety system. Federal food safety efforts will need full integration and sufficient support to meet these challenges.
The foods we consume begin as raw agricultural commodities grown in open fields or waters or raised in a variety of production facilities, such as barns, coops, pens, and feedlots. Rocks, stones, metal, wood, glass, and other physical objects can become part of raw ingredients. Further contamination can occur in the transport, processing, or distribution of foods because of equipment failure, accident, or negligence.
Foreign physical materials in foods can cause serious harm to consumers. Protective devices that remove or prevent physical hazards include metal detectors, magnets, sieves, traps, scalpers, and screens. Other effective means of
protection are production plant policies against the use of glass, wood, or nonferrous metal where possible; employee training; quality audits of ingredient suppliers; and sensory tests.
Federal agencies have established "defect action levels" for natural or unavoidable defects that do not affect human health, such as stems or pits in fruits and vegetables, bone in mechanically deboned meats, and microscopic insect fragments, which are primarily of aesthetic concern and do not present a safety hazard.
Summary Findings: The Changing Nature of Food Hazards
- Changes in the risk of infectious foodborne disease are due primarily to:
- changes in diet,
- increasing use of commercial food service and in food eaten or prepared away from home,
- new methods of producing and distributing food,
- new or re-emerging infectious foodborne agents, and
- the growing number of people at high risk for foodborne illnesses due to:
increasing number of elderly, and
increasing number of people with depressed immunity or resistance to infection.
- Changes in chemical hazards associated with the food supply must be monitored and evaluated; these include:
Increased use of dietary supplements and herbal products without requirements to meet specified safety standards;
new food components that mimic attributes of traditional food components;
introduction of new food technologies and processes;
changes in presence of food toxins and additives, including unintentional food additives; and
presence of physical hazards associated with new technologies or sources of foods.