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The CDC is continuing to investigate a multistate outbreak of Listeria monocytogenes infections linked to queso fresco and cotija cheese made by Rizo-López Foods.

As of Wednesday, a total of 26 people infected with the outbreak strain of Listeria have been reported from 11 states, the CDC . Of these 26 people, 23 have been hospitalized. Two deaths have been reported, one person from California and the other from Texas.

Reported illnesses have not necessarily come in quick succession, however. They began on dates ranging from June 15, 2014, to December 10, 2023. So, what happened, and how have they been linked?

The CDC previously investigated the outbreak in 2017 and 2021. "Epidemiologic evidence in previous investigations identified queso fresco and other similar cheeses as a potential source of the outbreak, but there was not enough information to identify a specific brand," the agency wrote. "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."

"In January 2024, Hawaii officials found the outbreak strain of Listeria in an aged cotija cheese product that was made by Rizo-López Foods," a spokesperson for the CDC told 乌鸦传媒 in an email. "This prompted an inspection at the Rizo-López Foods facility, where FDA found the outbreak strain on a container where cheeses are kept before they're packaged."

In its public notice, the CDC added that public health investigators are using the agency's PulseNet system to identify illnesses that may be part of the outbreak. The system manages a national database of DNA fingerprints of bacteria that cause foodborne illnesses. DNA fingerprinting is performed on bacteria using whole-genome sequencing (WGS).

"WGS showed that bacteria from sick people's samples from 2014 to present are closely related genetically," the CDC noted. "This suggests that people in this outbreak got sick from the same food."

Foodborne illness attorney William (Bill) Marler, JD, told 乌鸦传媒 that the technology used to detect the current outbreak and others like it has become incredibly sophisticated. So much so, he said, that many years later, individuals who have died are essentially "reaching their hands out of the grave."

"The problem is, when you have one case and even one case every once and a while, they may not have all the information about what did they eat, and where have they been," Marler said.

For Listeria in particular, a longer incubation period can also prove challenging, he said. Most people get sick within a number of weeks. Moreover, it is typically only the patients who are sick enough to be hospitalized who end up being tested and counted.

Furthermore, Listeria is sporadic because it's essentially an "environmental bug" that is "everywhere," Marler said. "When it gets into little crevices [or] cool, wet environments," such as those in production equipment for cheeses and deli meats, a biofilm develops and "sloughs off" into food that can be "enough to get someone sick or kill them."

There can be a cycle of equipment being cleaned, and the biofilm returning and sloughing off again within months, he added.

As for samples from years ago being closely genetically related to newer ones, it's similar to Charles Darwin's finches that "genetically, over time, became specialized," Marler explained. The same thing happens when Listeria stays in a food processing plant, and it's even faster at doing so. It "becomes a resident Listeria like finches in the Galápagos."

The CDC said that, overall, Listeria is pregnant people and their newborns, adults 65 and older, and people with weakened immune systems.

In the current outbreak, two people became sick during their pregnancy and one experienced a pregnancy loss, the CDC reported. "There are also two newborns in the case count for this outbreak because Listeria can be passed to newborns during pregnancy," the agency added.

The company linked to the outbreak has taken action. On January 11, Rizo-López Foods recalled an aged cotija cheese product after Hawaii state officials found Listeria in it, the CDC said. This week, the company . The company has also temporarily stopped producing and distributing these products while its investigation is ongoing.

In an emailed statement, Edwin Rizo, CEO and owner of Rizo-López Foods, wrote that the company "is a family-owned company I started as a small, local cheese supplier in 1990. We have grown to become a nationwide supplier by building a reputation for producing safe, high-quality dairy products for our consumers, including our own friends and family."

"This is the first time any product that we manufacture has been linked to a foodborne illness," Rizo added in part. "As soon as we were aware of this, we made the immediate decision to stop production and voluntarily recall all our products manufactured in our facility. We are working hard and diligently to find the root cause of the problem and take corrective actions to prevent it from happening again. The health and well-being of our customers is our top priority."

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