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

Commentary

Irradiation Pasteurization of Solid Foods: Taking Food Safety to the Next
Level

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In the 19th century, milk from diseased cattle produced in unsanitary
surroundings and distributed under filthy conditions to an increasingly
urbanized population sickened and killed consumers by the thousands (1,2).
Wide acceptance of the germ theory and the sanitary awakening that followed
led to vast improvements in animal health and hygiene, and the safety of
dairy products improved substantially. Dairy farmers in northern Europe
discovered that heating milk fed to their calves further reduced the risk
for tuberculosis in their herds, and after overcoming concerns that the new
thermal pasteurization technology would corrupt the dairy industry, destroy
the nutritional value of milk, and lead to serious public health problems,
the same level of protection was offered to human consumers a few decades
later (3,4). More recently, thermal pasteurization has been suggested for
eliminating low level contamination of juice by foodborne pathogens (5,6).
However, for the safety of solid foods that enter kitchens as raw
agricultural commodities, including meat, poultry, and seafood, we continue
to rely solely on animal health programs and sanitation. Therefore, as we
approach the 21st century, preventable illness and death caused by
vegetative bacterial and parasitic foodborne pathogens remain substantial
public health problems (7,8).

Irradiation pasteurization of solid foods with low doses of gamma rays,
X-rays, and electrons will effectively control vegetative bacterial and
parasitic foodborne pathogens (9-11). Public concerns, similar to those
raised against thermal pasteurization of milk, have been advanced in
opposition to irradiation pasteurization, and it has been claimed that if
we but paid more attention to sanitation and proper cooking, these products
could be safely consumed without introducing new technologies.

Perhaps. However, the residual risk for infection that remains after
state-of-practice sanitation during production, harvest, processing,
distribution, and preparation yields an unacceptable level of illness and
death. In addition, the admonition to properly cook works only if
culturally acceptable food preferences do not include undercooked and raw
foods. Increased interest (encouraged by the public health and nutrition
community) in fresh produce as part of a high fiber, low fat diet, further
reduces the effectiveness of proper cooking as a disease control strategy
(12).

Recent outbreaks of foodborne illness associated with undercooked meat and
uncooked fresh produce, and the emergence of the previously unrecognized
foodborne hazards that spawned the conference whose proceedings are
reported in this issue of Emerging Infectious Diseases, have stimulated
interest in methods of pasteurizing solid food without altering its raw
appearance and characteristics. Research is under way on a variety of
promising approaches, including pulsed energy, bright light, high pressure,
and other nonthermal technologies, but few are ready for immediate
application (13,14; Fed Reg 61:42381-83, 1997). Irradiation pasteurization,
on the other hand, is a well-established process with clearly documented
safety and efficacy that can be put into widespread use as quickly as
facilities can be sited and built (15).

Good practice guidelines and Hazard Analysis and Critical Control Points
programs (HACCP) can result in raw meat, poultry, seafood, and produce with
sufficiently low levels of pathogen contamination that irradiation doses as
low as 1 to 3 kGy yield adequate margins of safety for common foodborne
pathogens such as Campylobacter, Cryptosporidium, Escherichia coli,
Listeria, Salmonella, and Toxoplasma (9). No other control for
Campylobacter contamination of poultry meat is apparent, and other
approaches to ground beef safety have proven inadequate to prevent
intermittent low level contamination with E. coli O157:H7. Likewise, no
other solutions are immediately available to control pathogen contamination
of produce intended for raw consumption, and irradiation doses used appear
adequate for the bacterial and parasitic pathogens involved in recent
outbreaks (Donald Thayer, pers. comm.)

The food industry appears reluctant to fully embrace irradiation
pasteurization despite the obvious and painful failure of alternative
approaches to prevent foodborne infections. Much of this reluctance stems
from the perception that consumers reject the process and will refuse to
buy irradiated food. Indeed, surveys have shown considerable consumer
confusion and ignorance about food irradiation (16), and reports on public
antipathy toward things radioactive abound. However, consumer surveys also
demonstrate profound and growing public concern about microbial food
safety, and decreasing concerns about the safety of irradiated food (17).
Knowing as little about it as they appear to, approximately half of the
consumers surveyed have expressed willingness to try irradiated food if it
will decrease their risk for illness (16). In addition, when educated about
food irradiation, 90% of survey participants expressed interest in
purchasing irradiated foods; sampling such food increased interest to 99%
(18).

Irradiation pasteurization is not the cure for all food safety ills.
Pasteurization of any sort is no match for bad sanitation and substandard
practices, and irradiation pasteurization can be overwhelmed by large
numbers of pathogens. Just as obviously, foods produced and processed under
appropriate conditions that are then properly packaged and irradiated are
subject to postpasteurization contamination. In addition, the doses of
irradiation used to pasteurize fresh meat and poultry are not sufficient to
kill bacterial spores. Thus, if anaerobic packaging is the method used to
protect irradiated foods from postpasteurization contamination, Clostridium
botulinum could pose a risk if the cold chain is disrupted.

Vibrio infections associated with consumption of raw molluscan shellfish
can be prevented with irradiation pasteurization, but the Norwalk-like
viruses also frequently associated with raw shellfish appear to be more
radioresistant than vegetative bacterial pathogens. Levels of irradiation
an order of magnitude greater than pasteurizing doses for meat and poultry
also are necessary to inactivate hepatitis A virus. To reduce the risk for
foodborne hepatitis A and Norwalk virus infections, it will be necessary to
reduce the level of exposure of food to human feces. This is true
regardless of whether or not foods are to be pasteurized. Although
irradiation pasteurization will not eliminate all seafood-borne pathogens,
it will reduce the potential of seafood to cause illness. Seafood HACCP and
advances in viral diagnostics and environmental virology will help ensure
that prepasteurization conditions are sufficient to yield seafood
appropriate for irradiation pasteurization (19,20). Just as thermal
pasteurization works well for liquid foods like milk and juice, but not for
solid foods for which raw characteristics are desired, irradiation
pasteurization works well for meat, poultry, seafood, and soft fruit, but
wilts leafy vegetables and sprouts. That irradiation pasteurization does
not work for every food and every pathogen is poor justification for not
applying it for those food/pathogen combinations for which it has been
shown to work so well.

Consumer surveys have demonstrated public concerns over worker and
environmental safety that have also contributed to the reluctance of some
to build and use food irradiation facilities. These concerns are
appropriate and addressable. Because food irradiation and irradiation
sterilization of nonfood items like medical supplies are so well
established, proper facilities design and operating characteristics are
well known. The relatively short half-life of Cobalt 60 and its
insolubility in water reduce environmental concerns, which can be
eliminated altogether by using electricity-generated X-rays and electron
beams instead of a radioactive source. Proper education and training has
protected employees of irradiation sterilization facilities; employees of
food irradiation facilities should not be qualitatively different from
other employees in similar industries.

Thus, a broadly applicable solution to many of our food safety problems
exists and has existed for a number of decades. It is disappointing that
the public health community has been so silent for so long on this issue.
Faced with the liability of marketing hazardous foods, it is puzzling why
the food industry has not stepped into the vacuum created by this lack of
leadership from public health. Presentations at the Conference on Emerging
Foodborne Pathogens make it clear that new foodborne hazards are being
stacked on top of old, unresolved food safety problems—broadly applicable
solutions are desperately needed. Just as thermal pasteurization of milk
protected us from E. coli O157:H7 before we knew it was in raw milk,
irradiation pasteurization can protect us from tomorrow's emerging
foodborne pathogen.

Michael T. Osterholm* and Morris E. Potter†
*Minnesota Department of Health, Minneapolis, Minnesota, USA; and †Centers
for Disease Control and Prevention, Atlanta, Georgia, USA

References

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

URL: ftp://ftp.cdc.gov/pub/EID/vol3no4/ascii/osterhol.txt