Diagnosing Meningitis: The Spinal Tap
If a person has symptoms of meningitis, his or her physician may order a lumbar puncture, commonly called a spinal tap.
During a spinal tap, a needle is placed in the lumbar (lower) portion of the spinal canal and a small sample of cerebrospinal fluid (CSF) is removed. After the CSF is removed, it is cultured (the sample of CSF is incubated for a few days under conditions that promote the growth of microorganisms). If bacteria grow in the fluid, the type of bacteria causing the meningitis can be determined, and the most effective antibiotic can be prescribed.
Because viral meningitis is caused by a virus and not a bacterium, there will be no growth in the culture medium. This is why viral meningitis is also sometimes called aseptic meningitis.