Food Safety Magazine - June/July 2013
Food Safety Magazine - June/July 2013
Food Safety Magazine - June/July 2013
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SANITATION<br />
By Ewen C. D. Todd, Ph.D.<br />
The Burden of Listeriosis<br />
Taking a closer look at the<br />
food safety risks associated<br />
with Listeria monocytogenes<br />
Listeria monocytogenes is estimated to cause nearly<br />
1,600 illnesses each year in the United States<br />
and is responsible for more than 1,400 hospitalizations<br />
and 250 deaths. 1 Nearly all cases of<br />
Listeria infections (listeriosis) result from persons<br />
eating food contaminated with L. monocytogenes or<br />
affect newborn infants whose mothers eat contaminated<br />
food during pregnancy. Rates of listeriosis per 100,000<br />
individuals are relatively consistent across nations that<br />
report; estimates for cases of the febrile gastrointestinal<br />
form of the disease are rarely considered, even though<br />
a few outbreaks have been reported. 2 Outbreaks from<br />
L. monocytogenes are not frequent compared with those<br />
caused by pathogens like Salmonella and Clostridium<br />
perfringens, but they often generate national or even<br />
international notoriety. This is because: 1) the resultant<br />
infections are serious, with hospitalizations and deaths;<br />
2) they are often caused by lack of management oversight<br />
in manufacturing plants, lack of understanding of<br />
the nature of the pathogen or where errors by workers<br />
have been allowed to repeatedly occur; 3) these plants<br />
are then found to be typically out of compliance with<br />
existing regulations; and 4) the outbreaks have major<br />
economic consequences, especially if the products affect<br />
international trade. Outbreaks have involved a whole<br />
range of facilities, from small artisanal operations to<br />
well-established major processors. The implicated foods<br />
are typically deli meats and artisanal cheeses. However,<br />
case-control studies in the U.S. have implicated melons<br />
and hummus, and in 2011, a large outbreak associated<br />
with contaminated cantaloupes causing 147 cases and<br />
33 deaths reinforced a risk of listeriosis from consuming<br />
produce items. Most listeriosis<br />
outbreaks have been reported from<br />
Europe, the U.S., Canada, Australia and<br />
New Zealand, but the pathogen is likely<br />
causing illnesses in many other nations<br />
that do not investigate cases, which<br />
are mainly sporadic. Even in the U.S.,<br />
where listeriosis is nationally notifiable,<br />
it is believed that many cases are not<br />
recognized and reported. The fact that<br />
contaminated ready-to-eat (RTE) food is<br />
responsible for almost all illnesses—and<br />
the organism surprises us in the range<br />
of food it can contaminate in numbers<br />
large enough to cause outbreaks—has<br />
forced both government and the food<br />
industry to make a major effort to<br />
reduce the public’s exposure to the<br />
pathogen.<br />
Characteristics of Listeria<br />
monocytogenes<br />
Among pathogens, L. monocytogenes<br />
has distinctive characteristics that must<br />
be recognized before implementing prevention<br />
and control strategies applied to<br />
the food processing and food preparation<br />
environments. These include the<br />
extensive occurrence of the pathogen in<br />
the natural environment. Listeria spp.,<br />
including L. monocytogenes, are present<br />
in soil, water, sewage, vegetation and<br />
wild animal feces, as well as on the farm<br />
and in food processing facilities. 3 Farm<br />
animals can be asymptomatic or cause<br />
encephalitis, septicemia and abortions,<br />
and may be a source of L. monocytogenes<br />
on the farm. The pathogen can survive<br />
and grow at a wide range of temperatures<br />
(-1 to 45 °C); for instance, it can<br />
be a long-term resident in chilled food<br />
processing premises under high humidity,<br />
but it can also survive conditions of<br />
low water activity, such as under high<br />
salt concentrations. 4 Some strains can<br />
survive for long times under adverse<br />
environmental conditions and persist<br />
in niches in food processing equipment<br />
and associated drains, walls and<br />
28 F o o d S a f e t y M a g a z i n e