Notes from the Field: Listeria from Soft-ripened cheese


some nice cheese, via

some nice cheese, via

Via the ever helpful Morbidity Mortality Weekly Report, another alert about the dangers of foodborne-illness! The Minnesota Department of Health reported in late July 2013 two cases of invasive listeriosis, for which molecular analysis indicated a sole-source for infection. As an aside, the Minnesota Department of Health seems to be the hardest working state department of health, as evidenced by this alert about Salmonella from Guinea pigs, and this alert about Salmonella from phlebotomy that I found in the BIO230 archives. Way to go, Minnesota Department of Health!

Once the Centers for Disease Control and Prevention were notified, further analysis indicated that the isolate was also identical to an environmental isolate collected from a cheese producer in 2011. With this in place, several other cases were also identified by the CDC in last summer’s outbreak, resulting in one death and one miscarriage. All patients were interviewed to determine their “cheese exposure.” All patients indicated that they had likely eaten one or more of Crave Brothers Farmstead Cheese varieties (Les Frères, Petit Frère, or Petit Frère with truffles) during the likely time frame for infection, at either grocery stores or restaurants in the region. All of the cheeses were shipped as intact wheels to the point of sale, where they were cut and repackaged.

The manufacturer issued a voluntary recall when news of the outbreak was made public. Conjecture by the CDC suggested that the contamination arose during the manufacturing process. The process of pasteurization very effectively eliminates Listeria monocytogenes from milk, however in the cheesemaking process contamination can occur after the original pasteurization. The CDC recommends that strict sanitation and monitoring of contamination steps always be in place for cheesemakers, regardless of whether pasteurized milk is used.

The CDC also reiterated standard precautions to protect against infection by Listeria, which again bear repeating. The organism does not generally pose a significant health risk to the general population, however immunocompromised individuals can become quite seriously ill. Additionally, pregnant women can pass the organism onto the developing baby, and fetal infection due to Listeria is a significant cause of miscarriage. Because of these risks, at risk individuals are strongly advised to avoid any food that carries the potential for infection by Listeria.


About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on April 8, 2014, in You are what you eat. Bookmark the permalink. 2 Comments.

  1. Listeria is “found in soil and water and some animals, including poultry and cattle” (Listeria). Clearly, with cheese’s source being cattle, there is the risk that it may carry this bacteria. Although this disease does not readily affect everyone, certain people are at a greater risk. The news of this bacteria probably took a while to spread due to the limited number of cases in the area. With proper precautions, this bacteria can be avoided almost entirely. So the next time you crave some cheese…perhaps you should think twice!

    Abby Nicodemus
    MICRO MWF 11:00


    “Listeria.” Home. N.p., n.d. Web. 06 Sept. 2014.

    • Listeria unfortunately doesn’t make the cut of organisms in BIO230, however it will definitely be part of your workup when dealing with prepartum cases due to the risk of miscarriage. The large amount of dairy, and the popularity of raw milk in York County makes this a potentially significant risk!

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