DNA Fingerprinting of Listeria and the Whittier Farms Case
Determining Whether a Cluster of Listeriosis Cases is an Outbreak
In cases where a number of people in an area are diagnosed with listeriosis, health officials can use DNA fingerprinting to determine if the listeriosis cases are part of the same foodborne outbreak. For this purpose, health officials obtain isolates of Listeria monocytogenes bacteria from the people with listeriosis.
These isolates are tested pursuant to PulseNet system protocols using pulsed field gel electrophoresis (PFGE), a molecular subtyping technique. PFGE testing provides DNA fingerprints of the isolates. Matching (indistinguishable) DNA fingerprints indicate a listeriosis "outbreak" caused by a common source.
In the case of the listeriosis outbreak associated with Whittier Farms milk, Listeria isolates obtained from 4 people had matching DNA fingerprints. This establishes that these 4 victims of the outbreak were sickened by the same food source. The four four victims include three elderly residents and a pregnant woman from Worcester county, according to a Massachusetts Department of Public Health press release. Two of the elderly people have died.
The Roll of DNA Fingerprinting in Determining the Source of a Listeriosis Outbreak
To find the source of an outbreak, genetic fingerprinting and epidemiological evidence are used. The people sickened by Listeria bacteria with matching DNA fingerprints are interviewed (and/or their families are interviewed) to determine what they ate in the last 2 months (the incubation period for Listeria can be as long as 70 days). Health investigators (epidemiologists) look for common food sources and investigate all likely sources. Part of that investigation is testing processing plants (drains, equipment, etc.) and food products for Listeria monocytogenes. If Listeria is found, isolates will have PFGE testing done on them to determine if they match the outbreak strain of Listeria monocytogenes. If there is a match, health officials consider the food (food produced at the plant if the bacteria was found in the plant) the source of the outbreak.
If epidemiological evidence (patient interviews, receipts of purchase, etc.) associates a food product with an outbreak but Listeria is not found in the food product or the plant that produced it, that is generally adequate evidence to make a claim for damages against the manufacturer, distributor, and/or retail seller of the food.
In the case of the listeriosis outbreak associated with Whittier Farms milk, the Massachusetts Department of Public Health stated in a press release, “Samples collected showed product contamination.”
Attorney Fred Pritzker has extensive experience with Listeria lawsuits. To contact the firm, please call toll-free at 1-888-377-8900 or submit the firm’s free case consultation form for review by a Listeria attorney.
