Genetic Variability

The large genetic variability of microorganisms is the principal reason why so often some survive after any unfavorable environmental change. Some strains are hypermutable, which reinforces the potential for survival, and have very short generation times, with bacterial minutes comparable to human years. As Dr. Lederberg notes, microorganisms are opponents with whom we cannot race—on their terms.

Environment

Environmental factors also contribute to emergence. Hot, humid climates favor the growth of fungi and the production of mycotoxins. To borrow an example outside foodborne pathogens, an unusually wet season produced a sharp increase in the deer mice population and the consequent outbreak of hantavirus in the Four Corners area of the United States.

Behavior

Human actions and behavior directly affect food safety. People are vectors for disease, traveling far more often, farther, and more rapidly than ever before (3), and moving far more swiftly than rats, lice, and mosquitoes. Political boundaries frequently and perversely act as leaky sieves, letting diseases through unimpeded, while blocking measures for disease prevention, control, and treatment (1).

Urbanization

Urbanization is a major factor in emergence. Crowding increases human contact and opportunities for transmission. Particularly in developing countries, public health services lag far behind the rush from farm to city. Cities, especially in industrialized nations, are economic and governmental centers and harbor institutions of culture and learning. However, cities are also massive projects in the intensive monoculture of humans. With agriculture, it is entirely possible to carry out monoculture effectively and productively—esthetic considerations aside—if one provides for and tightly controls all essential inputs and conditions, monitors the process closely, and is prepared for prompt and effective intervention if something goes wrong. That hardly describes cities anywhere.

Raw Food Production

The effect of changes in raw food production and harvest practices on opportunities for foodborne outbreaks have been discussed. Centralized processing and wide distribution are the principal characteristics of the "new scenario," as compared to the "old scenario" of local production, home processing, and intrafamily consumption. A classic example is the recent Japanese outbreak of hemorrhagic Escherichia coli.

Denial

A behavior that encourages outbreaks is denying the existence of an epidemic—a practice more common in developing countries concerned about the effect of outbreak publicity on tourist trade and exports (4). One of our own attitudes is indifference to outbreaks perceived as commonplace and distant (5).

Economics

War and economic collapse provide unparalleled opportunities for disease outbreaks (e.g., cholera in central Africa). The infrastructure that provides clean water, community medicine, disease surveillance, and food control, even where it exists, is a fragile fabric, easily torn by economic, social, and physical disruption.

Technology

In spite of their benefits, technologies often bring new or enlarged risks. This is not an argument for returning to a state of nature. The invention of sausage doubtless increased the incidence of botulism; indeed, "botulus" is the Latin word for sausage. Without proper processing, any modern packaging that excludes oxygen can have the same effect.

Risk Factors

Factors such as age, illness, and medical treatment increase the risk for foodborne illness. Such increases also result from behavior that promotes the incidence of other diseases (e.g., AIDS).

Failure to Prevent and Control

The most common human action that adversely affects food safety is the avoidable lack of or failure to use effective prevention and control measures. That failure is why 85% of all outbreaks are traceable, about equally, to mishandling in homes or in food service establishments.

Interacting Factors

Figure

Figure. Problems causing foodborne disease in developing countries.

In much of the developing world, an interrelated and mutually reinforcing set of problems keeps foodborne disease at a high level (Figure). Approximately five million children under the age of 5 years living in the tropics die each year of malnutrition and diarrheal disease (6). Palliation is temporary; only economic and technical development can break through this net.

The contributing factors already mentioned would cause us problems, even acting singly. However, they interact, often synergistically. The combination of bacterial genetic variability and the ease and frequency of mutation of strains present a threat because the process enhances selection for new and more dangerous pathogens. Acid rain and recycling through ruminants may have encouraged the increased environmental durability of acid-tolerant E. coli O157:H7. The increasing popularity of marinades in the preparation of foods may have had the same effect.

The globalization of the food trade pulls together several of these contributing factors. One country's contaminated water leads to another country's contaminated raspberries. Refrigeration and controlled atmosphere can preserve pathogens, as well as foods, and spread them all over the world. The Salmonella Enteritidis outbreak from contaminated eggs in ice cream was a typically broad problem.

Technologic change combines many of these contributing factors. The intensive monoculture of plants and animals presents concentrated opportunities. For example, an outbreak of southern corn blight was attributed to the narrow genetic base of a popular hybrid corn. Human-guided plant genetics was defeated by the much more rapid genetic adaptability of microorganisms.

Indiscriminate use of antibiotics and the ability of microorganisms to exchange genetic information has led to increasing resistance. Minimal processing of food, warmly received by natural food lovers, is an open invitation to slightly more durable pathogens to take over the food supply. Centralized processing and mass distribution push us even further in the race Dr. Lederberg reminded us we cannot win. Immunosuppression, due to disease or medication, combined with the failure to take simple sanitary or health precautions make the emergence of pathogens inevitable.

Food Processing Technologies

Food processing technologies reduce our exposure to dietary pathogens in three ways, summarized by Professor E. M. Foster as "the three Ks": keep them out, kill all you can, keep the rest from growing.

One group of technologies removes or destroys microorganisms and naturally occurring toxicants by careful sanitation; heat treatment (e.g., cooking, retorting, pasteurizing, high temperature/short time treatment, ultrahigh temperature treatment, ohmic heating, and other newer techniques); radiation (widely useful and recently applied to all of our current methods); physical separation, (e.g., air separation, gravity tables, visual scanners, and other methods for reducing "natural and unavoidable defects" including gross contamination); dehydration; and new technologies (e.g., hydrostatic pressure, pulsed light).

A second group of technologies keeps contaminants well below dangerous levels. These include raw material quality control; careful sanitation; chemical preservation (i.e., fermentation, bacteriostats, pH control, water activity control, and controlled atmosphere storage); dehydration; and freezing and refrigeration.

The third group of technologies prevents recontamination through sanitation of the general environment and at the point of service, protective packaging, and proper handling to ensure packaging integrity.

Beyond these three groups of technologies are general principles governing the use of all such techniques. All foods require incoming quality control and careful sanitation. For nearly all foods except fresh produce and dried grains, one technology from each group listed above should be used. All technologies used must be applied effectively, or none is effective. These technologies must be used in combination, in a systems approach. Failure to apply properly a preceding technology can cause later technologies to increase microbiologic hazards. If oxygen is later excluded from improperly processed food by packaging (canning, foil, an oil layer), anaerobic pathogens, such as Botulinum, are free to multiply.