Listeria monocytogenes is a small, gram-positive bacillus that can grow in anaerobic or aerobic conditions. It is found widely in the environment in may be part of the fecal flora of many mammals, including healthy human adults. Initial symptoms of infection include nonspecific flu-like symptoms, nausea, vomiting, cramps, diarrhea and fever. There are few clinical features that are unique to listeriosis. Therefore, clinicians must consider a variety of potential causes for infection, including viral infections (influenza) and other bacterial infections that may cause sepsis or meningitis. Symptoms can develop at any time from 2 to 70 days after eating contaminated food. Except for vertical mother–fetus transmission, most cases of listeriosis begin with ingestion of the organism from a food source. Most healthy adults and children who consume contaminated food experience only mild to moderate symptoms. People with poor immune function are at much higher risk of severe, life-threatening forms of listeriosis.

H&R Listeria provides a rapid detection of Listeria monocytogenes directly from faecal samples.