Listeriosis - Diagnosis 

Listeriosis can be diagnosed with a blood test. Further testing is only required if it's thought that the infection has spread to your nervous system. These tests may include:

• a computerised tomography (CT) scan – a series of X-rays that are put together by a computer to produce a detailed image
• a magnetic resonance imaging (MRI) scan – where a strong magnetic field and radio waves are used to produce detailed images of the inside of your body
• a lumbar puncture (see below)

A lumbar puncture, also known as a spinal tap, is used to test a sample of fluid from the spinal cord. The fluid is called cerebrospinal fluid (CSF) and surrounds and protects the brain and spinal cord.

A hollow needle is inserted into the lower part of your back to draw out a sample of CSF. If the infection has spread to your nervous system, listeria will be present in the CSF.