[Emerging Infectious Diseases * Volume 3 * Number 4 * October - December 1997]

Special Issue

Foodborne Illness: Implications for the Future

Richard L. Hall
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      Many outbreaks of foodborne illness, even those involving newly
      recognized pathogens, could have been avoided if certain
      precautions had been taken. This article will draw on existing
      information to suggest realistic measures that, if implemented,
      are most likely to avert or diminish the impact of new
      foodborne disease outbreaks.

I do not see microbiologic infections as totally different from other food
hazards, or microorganisms as totally different from other life forms. We
are all hosts and prey, parasites and predators. Even though we differ in
size, complexity, and weaponry, we employ many similar strategiesthe
result of a shared planet, and a substantially shared genetic base. That is
also why we have much to learn from animal disease surveillance.

Writing on emerging diseases, many argue forcefully for a broad and
well-integrated view (1,2); however, aspects absolutely essential to
understanding the problem are often omitted. This short article will
doubtless make the same error. So, as Shakespeare had Prologue plead at the
opening of Henry the Fifth, "Piece out our imperfections in your minds."

Factors Contributing to Emergence

Outbreaks occur whenever pathogenic agents in sufficient number or quantity
encounter a susceptible population without effective interceptive measures.
Then, if we did not expect it, we say "it emerged."

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 raceon 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 productivelyesthetic considerations asideif 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
epidemica 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

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.


 [Figure Not Available in ASCII]
 Figure. Problems causing foodborne disease in developing countries.

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.

The Role of Public Health Measures

Achieving optimum public health requires many measures, each necessary but
not sufficient in itself. The most basic measure is clean water, as recent
incidents with strawberries and other fresh produce washed with
contaminated water illustrate.

Effective food control structures (e.g., statutory and regulatory
frameworks and inspection and enforcement agencies) are essential. A
surveillance system has always been required and should be directed to
populations at high risk. Newer methods of typing pathogens, faster
response times, and enhanced analytical sensitivity are making those
systems far more effective than they have been.

Family health programs and education are equally necessary. Food safety
still depends heavily on how each of us chooses and uses (or abuses) our
food, and each of us is not expert.

The Roles of Food Processing

We process food for the following main reasons: nutrition, safety,
preservation, distribution, and esthetics. Cooking typically increases
protein digestibility and destroys antinutrients. Fortification and
enrichment add, restore, or increase essential nutrients. Cooking and
canning destroy pathogenic organisms; cooking and steeping remove natural
toxicants, such as cyanide from cassava. Canning, dehydration, salting,
smoking, and preservatives, combined with proper packaging and storage,
decrease spoilage. Canning, freezing, refrigeration, and controlled
atmosphere storage provide variety and year-round availability. Flavors,
colors, pre-sale preparation, and stabilizers that prevent separation or
crystallization increase consumer appeal and convenience.

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.

Future Options

Food safety objectives must be established. There is a clear need for
priorities and for employing the "principle of commensurate effort" (i.e.,
applying effort to risks in the order of their probable impact).

There is also the need for a broad view (1,2). The interaction of several
factors, not all of which can be seen in advance, makes a team approach
essential.

More effort at understanding the evolution of virulence (7) could provide
us with insights on the genetic characteristics and the environmental
conditions needed to minimize risk. The 1918-19 influenza epidemic can be
used as an example; the present search for its genetic makeup suggests the
value of prior knowledge. Knowing or estimating the probability of present
or future virulence could prepare us for the more effective use of other
measures. These include newer, faster, more sensitive methods of detection.

Improved detection would lead to more effective prevention and control
measures. The need to establish priorities suggests here, as in cancer
research, the value of biomarkers. Biomarkers are genetic or biochemical
indicators of impending risk in the potential pathogen, preceding clinical
or epidemiologic indications. Such biomarkers might indicate potential
virulence, increased environmental durability, or increased resistance to
heat, cold, unfavorable pH, preservatives, or antibiotics.

We need to apply available knowledge more effectively. Most outbreaks of
foodborne disease are due to mishandling food in ways we already know how
to avoid. The points that follow are not new, but as our food supply
increases in complexity and geographic reach, these weapons must grow
apace.

Clean water, public sanitation, disease surveillance, and food control are
more important than ever. The value of effective disease surveillance has
been demonstrated. But what we now have and do is not enough. A national
response team must be created. Data should be shared more broadly
(electronic linkage of laboratory and surveillance results) if we are to
cope effectively with a global food supply, multistage processing by
different firms at different locations, and national and international
distribution. The effective application of these resources requires a
Hazard Analysis and Critical Control Points (HACCP) approach (8).

Private health measures must grow in effectiveness and reach. We must make
continuing and increasingly effective use of food processing technologies
that reduce microbiologic risks. HACCP cannot be generic or static; it must
be adapted to each specific product and processing facility and must be
updated with continuing feedback on the hazards to be avoided. HACCP,
fortified by the public health measures just described and by the results
of the research discussed at this conference, will enable the food
processing industry to meet the challenges of emerging pathogens.

Even with the steps just described, approximately 85% of all outbreaks
occur as a result of food mishandling in food service establishments or
homes. We need to extend HACCP principles to the food service sector as
well. HACCP probably cannot reach into homes. If we are to communicate
better, we need first to find out what consumers already know, what they
want to know, and what they need to know. In short, if we are to educate
effectively, we must have direct evidence of how well the information
process is working.

Finally, we will never succeed in achieving desirable consumer
risk-management practices until consumers understand the inevitability of
some risks and minimize them. Food risks have been categorized into six
groups in decreasing order of size: microbiologic, nutritional, natural
toxicant, environmental contaminant, pesticide residues, and food additives
(9). The take-home message on food safety for all of us, as consumers, can
be summed up in three words: sanitation, variety, moderation. Sanitation
deals effectively with microbiologic risks; variety and moderation deal
with nutritional risks, minimizing the impact of the four remaining risks
to the extent they are even potentially insignificant. Sanitation, variety,
and moderation are within our own control as individual consumers. That is
doubtless why we have done only a mediocre job of implementing them. Unless
all of us c
an and do pursue these three objectives effectively, we are all
at some unnecessarily increased risk.

Address for correspondence: Richard L. Hall, 7004 Wellington Court,
Baltimore, MD 21212; fax: 410-377-2909.

References

  1. Farmer P. Social inequalities and emerging infectious diseases. Emerg
     Infect Dis 1996;2:259-69.
  2. Vidaver AK. Emerging and reemerging infectious diseases. American
     Society for Microbiology News 1996;62:583.
  3. Wilson M. Travel and the emergence of infectious diseases. Emerg
     Infect Dis 1995;1:39-46.
  4. Vidaver AK. Emerging and reemerging infectious diseases. American
     Society for Microbiology News 1996;62:585.
  5. Lederberg J, Shope RE, Oaks SC. Emerging infections: microbial threats
     to health in the United States. Washington (DC): National Academy
     Press; 1992.
  6. Snyder JD, Merson MH. The magnitude of the global problem of acute
     diarrhoeal disease: a review of active surveillance data. Bull World
     Health Organ 1996;60(4):605-13.
  7. Ewald P. Guarding against the most dangerous emerging pathogens:
     insights from evolutionary biology. Emerg Infect Dis 1996;2:245-56.
  8. International Committee on Microbiological Safety in Foods. HACCP in
     microbiological safety and quality. In: Microorganisms in Food. Book
     4. Oxford: Blackwell Scientific Publications Ltd.; 1988. p. 28-43.
  9. Wodicka VO. Wodicka rates food additive hazard as low. Food Chemical
     News 1971;12(49):11.

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Emerging Infectious Diseases
National Center for Infectious Diseases
Centers for Disease Control and Prevention
Atlanta, GA

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