In an investigation of a listeriosis outbreak in Ontario, Canada, during November 2015–June 2016, Public Health Ontario identified pasteurized chocolate milk as the source. Because listeriosis outbreaks associated with pasteurized milk are rare in North America, these findings highlight that dairy products can be contaminated after pasteurization.
Listeria monocytogenes is a formidable pathogen acquired primarily through contaminated food. Invasive listeriosis is a reportable disease in Ontario, Canada; ≈50 case-patients (0.4 cases/100,000 persons) have been reported annually since 2005 (1). Recent outbreaks of listeriosis in North America have been associated with delicatessen meats, soft cheeses, raw produce, and unpasteurized dairy products (2–4). However, listeriosis outbreaks linked to pasteurized fluid milk are rare.
A study in the United States reviewed 83 fluid milk-associated disease outbreaks during 1990–2006; however, only 1 outbreak was attributed to L. monocytogenes (5). We report an outbreak of listeriosis associated with pasteurized chocolate milk in Ontario, Canada.