Each year I update this post with a new description of an outbreak of Listeria monocytogenes in ice cream. This year, it’s L. monocytogenes in milk shake machines that has killed 3 people as of this writing, and L. monocytogenes in soft serve to go ice cream cups that I mentioned in class on Monday. Last year, it was an outbreak of L. monocytogenes, which sickened 28 people across 11 state and lead to one death, that was linked to ice cream produced by Big Olaf Creamery. As we will learn in class later in the semester, an outbreak of Listeria monocytogenes in Blue Bell ice cream changed our understanding of minimum infectious doses for L. monocytogenes.
One of the aspects that makes L. monocytogenes a challenging pathogen to control in the food safety environment is its ability to form biofilms. A follow-up study to a 2015 outbreak in hospitalized patients demonstrated that extensive and time-consuming sanitation practices were required to remove L. monocytogenes from contaminated milk shake machines. While we will discuss other aspects of L. monocytogenes physiology and disease presentation that make it a challenging pathogen to control later in the semester, a brief summary of factors that contribute to L. monocytogenes in ice cream, as well as a description of outbreaks can be found here.
Image source: https://www.cdc.gov/listeria/index.html