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Listeria and Pasteurized Milk

By Pritzker | Ruohonen

It has long been known that the pasteurization process effectively kills many pathogenic organisms, including the bacteria Listeria monocytogenes, which should make pasteurized milk and other products safe for human consumption.  However, an outbreak of listeriosis in Massachusetts has lequestioned the safety of pasteurized milk.  Pasteurized milk products from Whittier Farms resulted in the deaths of three elderly men and sickened two pregnant women, resulting in one miscarriage. 

Pasteurization is by no means cutting edge technology, developed by Louis Pasteur and Claude Bernard in 1862. Listeria outbreaks are also anything but new to Massachusetts. A Listeria outbreak occurred in the state in 1983. The source of the 1983 outbreak was whole and 2% pasteurized milk.

In 1988, the CDC’s Morbidity and Mortality Weekly Report released a story dealing with the effectiveness of pasteurization to control listeriosis. The CDC evaluated multiple studies testing varying amounts of Listeria contamination in milk and concluded that the process does indeed protect against listeriosis.  The report also quoted the World Health Organization (WHO) Working Group on foodborne listeriosis which stated that "pasteurization is a safe process which reduces the number of L. monocytogenes occurring in raw milk to levels that do not pose an appreciable risk to human health."

The United States and the WHO agree that pasteurization works. Even though the process has been proven to work through scientific experiments, Massachusetts seems to have a problem keeping Listeria out of pasteurized milk, most recently in products from Whittier Farms.

Whittier Farms has undergone intense investigation to get to the source of the contamination. According to an article from the Worcester Telegram:

The findings do not pinpoint where contamination of the milk occurred, according to state officials, but they do suggest that listeria bacteria colonized somewhere in the processing plant, and entered the milk products at some point after pasteurization and during the production process.

The findings show that the pasteurization process is not to blame. There were problems at Whittier with introducing Listeria to the milk after the process had killed the bacteria previously present in the milk. If Listeria is going to find its way into processed milk, why pasteurize it to begin with?

To quote Louis Pasteur, “Let me tell you the secret that has led me to my goal.  My strength lies solely in my tenacity.” Pasteur invented a process that effectively eliminates bacteria such as Listeria, but to reach the goal of fully preventing the contamination of milk in the nation’s dairies, the government and dairies themselves will require tenacity and determination to protect products after the pasteurization process.

Full post as published by Food Poisoning Law Blog on January 24, 2008 (boomark / email).