Monday, November 1, 2010

It's Not About Raw Milk!

Listeria monocytogenes in cheese is a sanitation problem, not a raw milk problem

Listeria monocytogenes is all around us. It may be in floor drains. It may be in sinks and on faucets. It may be on counters, knives and cutting surfaces. But Listeria monocytogenes does not have to be in our food, if producers – including artisanal cheese manufacturers – follow proven sanitation practices.

An eFoodAlert reader posted this comment/question in response to one of my recent articles Estrella Family Creamery's run-in with FDA and Washington State Department of Agriculture:
"Why not label raw milk, aged cheese as a food to be avoided by certain people and let me take my risks and enjoy cheese with flavor? P.E., you want "food as safe as we can make it?" Sterilize it all? Do you have any information about LM deaths in France and/or their testing/monitoring protocols? I think it would add much to this discussion."

I've done some checking, and have found that the information available from France is limited, and not completely current. Fortunately, data from Canada and the USA are more accessible.

A 2005 article, which appeared in Eurosurveillance, reported eight outbreaks of Listeria monocytogenes in France between 1992 and 2002 – three of them linked to raw milk cheese. The cheese outbreaks involved a total of 53 illnesses (36 in 1995, 14 in 1997, and 3 in 1999). It does not appear that any deaths were reported.

In 2008, the Province of Québec (Canada) experienced a serious outbreak of Listeria monocytogenes that was traced to the consumption of contaminated cheeses. Twenty-two people, including three newborn infants, were infected with the pathogen. One person died. The cheese was distributed to hundreds of independent cheese shops, and spread Listeria monocytogenes to knives, counters and other areas in those shops. All cheese products – whether made from raw milk or pasteurized milk – that may have contacted the contaminated surfaces and implements were recalled from the public due to the risk of cross-contamination.

Cheese made using pasteurized milk is just as susceptible to Listeria contamination as is raw milk cheese. Marlerblog has posted a compilation of recent outbreaks, illnesses and recalls due to Listeria monocytogenes contamination of raw and/or pasteurized dairy products in the United States (2010 year-to-date). Three recalls, including one outbreak, were cheese-related. All three involved queso fresco cheeses that were made using pasteurized milk. None of the Listeria-contaminated cheeses were manufactured using raw milk.

The University of Vermont maintains an active research program in food microbiology, and hosts the Vermont Institute for Artisan Cheese. The Institute's research and education programs provide technical support to artisan cheese producers in Vermont and throughout the United States. Research carried out by Institute faculty members, including Dr. Catherine Donnelly and Dr. D.J. D'Amico, clearly demonstrates that the microbiological safety of artisanal cheeses depends on good sanitation and proper handling, rather than on whether or not the milk was pasteurized. Here are a few of the observations and conclusions published by D'Amico and Donnelly.

From Journal of Food Protection, vol. 71(8): pp. 1580-1589. 2008
"The findings of this study indicate that most raw milk intended for farmstead cheesemaking was of high microbiological quality according to current U.S. and EU standards and in comparison with quality reports from the state of Vermont, the United States as a whole, and other countries."

"The variation from farm to farm, regardless of species, indicates that some operations practice strict hygienic controls but that additional effort is needed at other operations."

From Journal of Food Protection, vol. 71(8): pp. 1563-1571. 2008
"Independent of the milk type, cheeses held for 60 days supported growth from very low initial levels of L. monocytogenes introduced as a post-process contaminant. The safety of cheeses of this type must be achieved through control strategies other than aging, and thus revision of current federal regulations is warranted."

From Journal of Food Protection, vol. 72(12): pp. 2499-2507. 2009
"Persistent contamination . . . is likely due to a combination of several factors. Areas that are difficult to clean or access, such as drains, also provide protection, giving cells time needed to establish. Persistent strains may possess increased resistance to sanitizers and disinfectants and thus survive the stress incurred through cleaning and disinfection, especially if these procedures are carried out insufficiently."

The bottom line, whether producing cheese or any other food, is that food safety depends on Good Manufacturing Practices and close attention to cleanliness and sanitation. Anything less is a recipe for product recalls and food-borne disease outbreaks.

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  1. Chère Madame,
    Quelques informations sur la situation française : à ma connaissance, aucune épidémie de listériose du fait de la consommation de fromage n'a été constatée en France depuis 2002. Néanmoins, en France comme dans le reste de l'Europe, l'incidence de la listériose augmente régulièrement. Pour la France, les chiffres se trouvent ici :
    Vous trouverez une discussion approfondie de ce sujet dans le document suivant :
    Avec mes sincères salutations,
    Olivier CERF
    Ecole vétérinaire d'Alfort

  2. @Olivier.-Merci bien de votre contribution très valable.

    For the benefit of readers who do not understand French, following is my translation of Olivier's comment:

    Dear Madam,
    Some information on the French situation:
    To my knowledge, no cheese-related outbreak of listeriosis has been noted in France since 2002. Nevertheless, in France – as in the rest of Europe – the incidence of listeriosis is on the rise. The data for France can be found here:

    You will also find an in-depth discussion of this subject in the following document:

    With my sincere regards,
    Olivier CERF
    Alford Veterinary School

  3. From Bill Riedel, by email:

    "It is my opinion that any discussion of sanitation to prevent listeria that does not include a mention of legal use of bacteriophages both in products and plant sanitation is incomplete. In the USA the Food and Drug Administration has amended the US food additive regulations to provide for the safe use of a bacteriophages on ready-to-eat meat against Listeria monocytogenes (see ) and ) . The idea that ready-to-eat meat can be treated if contaminated with Listeria bacteria while a doctor could not get a pharmaceutical grade phage therapy product when faced with a patient suffering listeriosis, strikes this author as absurd."


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