Their findings prompt them to caution consumers, especially
elderly people with weaker immune systems and those undergoing cancer
treatments that compromise immune systems, to steer clear of the deli department
meats.
Not all supermarket chains had a problem, but in some that
did, Listeria showed up every time for three sets of sampling and testing.
The research team says this indicates
that standard cleaning procedures in retail delis may not eradicate Listeria monocytogenes bacteria,
which can cause a potentially fatal disease in people with vulnerable immune
systems.
A study led by Haley Oliver, assistant professor of food science, found that 6.8 percent of samples taken in 15
delis before daily operation had begun tested positive for the food-poisoning bacteria.
In a second sampling phase, 9.5 percent
of samples taken in 30 delis during operation over six months tested positive
for the bacteria.
In 12 delis, the same subtypes of the
bacteria cropped up in several of the monthly samplings, which could mean that L. monocytogenes can persist in
growth niches over time.
"This is a public health
challenge," Oliver said.
"These data suggest that failure to
thoroughly execute cleaning and sanitation protocols is allowing L. monocytogenes to persist in some
stores. We can't in good conscience tell people with weak immune systems that
it is safe to eat at the deli."
In healthy individuals, eating food
contaminated with L. monocytogenes
may lead to common food poisoning symptoms such as diarrhea or an upset
stomach.
But the bacteria can cause listeriosis -
a serious systemic infection - in immunocompromised people such as the elderly,
infants and children, pregnant women and people with HIV.
In severe cases, L. monocytogenes can pass through the intestinal membrane and
into the bloodstream or cross the blood-brain barrier. The bacteria can also
cross the placental barrier in pregnant women, which can trigger abortion.
This is the bacteria that resulted in 22
deaths among consumers of processed meats from a Toronto processing plant run
by Maple Leaf Foods Inc.
Ready-to-eat deli meats are the food
most associated with L. monocytogenes,
which, unlike Salmoneall and E. coli, can grow at refrigerator temperatures.
“Stringent control measures and inspections
have tamped down the presence of L.
monocytogenes at meat processing plants, but there are no regulations
specific to Listeria for
retail delis, the researchers say.
Recent risk assessments suggest that up
to 83 percent of listeriosis cases linked to deli meats are attributable to
products contaminated at retail.
"It's kind of the Wild West,"
Oliver said.
"Manufacturing has a zero-tolerance
policy for Listeria, but that
dissipates at the retail level.
“The challenge of developing systematic
cleaning procedures for a wide variety of delis - which are less restricted
environments than processing plants - can make Listeria harder to control," he said.
Oliver and her team collected and tested
swabs of surfaces that come into frequent contact with food, such as meat
slicers and counters, and surfaces that typically do not.
