Listeriosis outbreaks associated with soft cheeses have been trending up in the United States since 2006, with high percentages of pregnant women and Hispanic people among those sickened. The risk for infection increases up to 160-fold when such cheeses are made from unpasteurized, raw milk.

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The outbreaks linked to soft cheese from 1998 to 2014 resulted in 180 confirmed illnesses, 17 deaths and 14 fetal losses. The vast majority of patients, 88 percent, required hospitalization, according to a report published this week by scientists at the Centers for Disease Control and Prevention.

Using data from the Foodborne Disease Outbreak Surveillance System, CDC scientists reviewed 58 listeriosis outbreaks, 30 percent of which were related to soft cheeses. Most were “Latin-style” soft cheeses like queso fresco. Of the 116 patients for whom ethnicity was known, 33 percent were Hispanic.

“Consumption of contaminated soft cheese made under insanitary conditions continues be a common cause of listeriosis outbreaks in the United States,” according to the report from Kelly Ann Jackson, L. Hannah Gould, Jennifer C. Hunter, Zuzana Kucerova and Brendan Jackson. Multiple types of soft cheeses have been implicated in outbreaks, with most outbreaks linked to Latin-style soft cheese.

“These outbreaks disproportionately affect Hispanic pregnant women and their neonates, a group with 24 times higher risk for listeriosis than that of the general U.S. population.”

The proportion of listeriosis outbreaks linked to soft cheese made from pasteurized milk was significantly higher from 2007 to 2014, with 12 outbreaks, or 33 percent, than from 1998 to 2006 when there was one such outbreak that accounted for 5 percent of Listeria monocytogenes infection outbreaks.

“…we did not observe a similar increased proportion of outbreaks linked to other foods during the same period,” the researchers wrote. They concluded the increase in the Listeria monocytogenes outbreaks associated with soft cheese could be due to a number of factors, including:

  • the growing U.S. Hispanic population, which increased from 11 percent in 1998 to 17 percent in 2014 ;
  • a 2.5-fold increase in per capita consumption of cheese from 1980 to 2013;
  • consumer demand for certain types of cheeses; and
  • an increase in the number of small producers, some of which had sanitary deficiencies.

Data analysis showed the use of unpasteurized, raw milk to produce soft-ripened cheese greatly increases the danger.

“The risk for listeriosis per serving is estimated to be 50- to 160-fold greater for cheese made from unpasteurized milk than pasteurized milk,” according to the research report published in Emerging Infectious Diseases.

“Consumers, particularly persons at high risk for listeriosis, are advised to avoid unpasteurized milk and dairy products made from unpasteurized milk.”

Soft cheeses made with pasteurized milk, including commercial cottage cheese, cream cheese, and processed mozzarella, are generally considered safe, according to the CDC and the Food and Drug Administration. However, the researchers wrote, some soft cheeses made with pasteurized milk, particularly Latin-style soft cheeses, have been produced in facilities with improper processing conditions, resulting in contamination.

Because consumers cannot evaluate the production environment or processes used to make cheese, the research team advises people at higher risk for listeriosis — the elderly, persons with immunocompromising conditions, and pregnant women — to carefully consider whether to consume Latin-style and other soft cheeses implicated in previous outbreaks.


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