DNA Fingerprinting Aids CDC ID of 10yr Listeria Source

The CDC's timeline linking one source after a period of ten-years of outbreaks substantiates the fact listeria is a hardy germ that can be difficult to fully remove from food processing facilities. Listeria can also survive in the refrigerator and easily contaminate other foods and surfaces.

DNA fingerprinting is performed on bacteria using using the PulseNet system to identify illnesses that may be part of this outbreak. The CDC PulseNet manages a national database of DNA fingerprints of bacteria that cause foodborne illnesses.

By utilizing whole genome sequencing (WGS) bacteria from sick people’s samples from 2014 to present were identified as closely related genetically. The conclusion was they got sick from the same food:

• CDC investigated a multi-state outbreak in 2017 and 2021.

• The CDC reopened the investigation in January 2024 after new illnesses were reported in December 2023 and the outbreak strain was found in a cheese sample from Rizo-López Foods. 

• On January 11, 2024, Rizo-López Foods, Inc. recalled the aged cotija cheese product after Hawaii state officials found Listeria in it.

• On February 6, 2024, Rizo-López Foods, Inc. recalled all cheese and other dairy products made in their facility. They have also temporarily stopped producing and distributing these products while their investigation is ongoing.

Investigation Details | Listeria Outbreak Linked to Queso Fresco and Cotija Cheese | CDC

Unrelated to the cheese and dairy products from this outbreak is a concern about Enoki Mushrooms

Because of recent outbreaks, the CDC is currently working to understand the risk of Listeria infection from enoki mushrooms. While this work is happening, the CDC advises people who are pregnant, aged 65 or older, or have a weakened immune system to not eat raw enoki mushrooms. Instead, cook enoki mushrooms thoroughly, and ask that restaurants cook them thoroughly.  See more scientific papers on the CDC Listeria publications page.

The true number of sick people in this outbreak is likely higher than the number reported, and the outbreak may not be limited to the states with known illnesses. This is because some people recover without medical care and are not tested for Listeria. In addition, recent illnesses may not yet be reported as it usually takes 3 to 4 weeks to determine if a sick person is part of an outbreak.

According to the CDC website:

• An estimated 1,600 people get listeriosis each year, and about 260 die.
• Listeria is especially harmful for some people:
  • Older adults (65 and older)
  • People who have weakened immune systems (have health problems or take medicines that lower the body’s ability to fight germs and sickness)
  • Pregnant people and newborns
  Be aware of foods to avoid if you are in any of these groups, choose safer foods to protect your health or your pregnancy. Prevent Listeria | Listeria | CDC

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