Listeriosis is usually diagnosed through laboratory tests, such as bacterial culture, that grow Listeria from a body tissue or fluid, such as blood, spinal fluid, or urine. In some cases, spinal fluid or urine samples may also be tested. Polymerase chain reaction (PCR) is another detection method available for diagnosis of listeriosis in humans. The Christie-Atkins-Munch-Peterson (CAMP) test is another useful confirmatory test for Listeria spp that can help confirm species by testing for haemolysis enhancement on sheep blood agar in the presence of other haemolytic bacteria. Magnetic-resonance imaging (MRI) is used to confirm or rule out brain or brain stem involvement. Early diagnosis and treatment of listeriosis in high-risk patients is critical since the outcome of untreated infection can be devastating.