Canada’s Public Health Agency is investigating five linked cases of listeria in four Canadian provinces unrelated to the recent outbreak traced to Dole salads packaged in Springfield, Ohio, according to an email obtained by the Burnaby NOW.
The cases, one each in B.C., Alberta and Quebec and two in Ontario, share a similar DNA fingerprint, or matching pulsed-field gel electrophoresis (PFGE) patterns, according to the Feb. 1. email from a Health Canada communications advisor to counterparts in the affected provinces’ health ministries.
Canada’s chief public health officer, Dr. Greg Taylor has flagged the cluster of cases, according to the email, and the health agency’s outbreak management division was going over food questionnaires from some of the cases to decide whether a national committee should be formed to look into the outbreak.
The chief public health officer had asked the public affairs branch to consider issuing a public health notice, according to the email.
The Public Health Agency confirmed Wednesday the cluster of cases had been identified through the PulseNet Canada surveillance system, a national database of PFGE patterns, and that the cases were unrelated to the Dole outbreak but no “specific source” had been identified.
The agency has also flagged another cluster of six listeria cases, including one death, that could be related to the five cases.
Reported in the same provinces between July 2015 and January 2016, they “have a similar genetic fingerprint to the other five cases,” according to an agency email statement.
“If the ongoing review identifies common food items or other cases of illness that are determined to be related to each other, then the agency will activate a national outbreak investigation coordinating committee (OICC) in accordance with the foodborne illness outbreak response protocol to further investigate the source of these illnesses,” the agency email states.
A 'simple test'
Similar or even matching (PFGE) patterns don’t necessarily mean the cases share a common source, according to SFU molecular biology and biochemistry professor Fiona Brinkman, whose Burnaby Mountain lab is developing computer tools to better study and track outbreaks.
She calls the PFGE technique a “simple test” that only looks at chunks of a bacteria’s DNA and can show chance similarities between strains.
“It’s implying that portions of the DNA are similar,” she told the NOW. “It is a fingerprint, but it’s not a high-resolution fingerprint.”
That leaves public health officials in the tough spot, she said.
“The biggest challenge with outbreaks is, when do you have an outbreak that you really need to communicate to the public that this is something to care about,” she said.
Agencies could go public with outbreaks more quickly, she said, if they had an integrated, efficient way to compare the whole genome, or complete DNA, of the microbes infecting different people – something she and her team are working on with their IRIDA (integrated rapid infectious disease analysis) project.
“This is exactly why we’re doing this research,” Brinkman said. “We’re trying to come up with this better computation tool that the minute these isolates come out that they get genomically sequenced and we’d basically be able to flag them very accurately very quickly and be able to say, ‘Oh, these are absolutely a match, so there’s definitely something going on here.’”
Requests for specific information about the B.C. listeria cases have not been answered by the Public Health Agency. Check back for updates to this story.
Health Canada listeria facts
Listeria is a type of bacteria found in food, soil, plants, sewage and other places in nature, and eating food with Listeria on it can cause a serious disease, called listeriosis.
Foods contaminated with listeria may look, smell and taste normal. Unlike most bacteria, it can survive and sometimes grow on refrigerated foods but can be killed by cooking food properly.
Those at highest risk of serious illness include pregnant women and unborn or newborn children, adults 65 and over, and people with weakened immune systems.
High-risk food items include raw meat and vegetables, unpasteurized milk and cheeses, ready-to-eat meats such as hot dogs and deli meats, and refrigerated smoked seafood and fish.
The mild symptoms of listeriosis include fever, muscle aches, nausea or diarrhea. Severe symptoms include headaches, confusion, loss of balance and neck stiffness.
The mild form usually begins about three days after eating heavily contaminated food. The incubation period for the more serious form is usually much longer—up to 70 days after exposure.
Listeriosis can be treated with antibiotics, but early diagnosis is key, especially for people in high-risk groups.
For more informations, visit www.phac-aspc.gc.ca.
