While many different pathogens can cause foodborne illnesses, there are only a few pathogens for which sources within food processing and handling environments have been directly linked to foodborne illness cases and outbreaks. Listeria monocytogenes, one of the organisms most troubling to refrigerated and frozen food producers, is a particularly problematic pathogen in this regard.
Listeria monocytogenes is mainly found in moist conditions, including soil, surface water and decaying vegetation. It is also salt-tolerant and can withstand and grow in temperatures below 1°C, making it an extremely survivable pathogenic organism for nearly any processing environment, including those that process raw materials using colder temperatures. Contamination can come from these raw materials, from the air and from food workers and food processing environments.