Aseptic. Meningitis is an inflammation of the outer coating of the brain. A spinal tap will show inflammatory cells in spinal fluid. Bacteria will be seen and cultured if present. If nothing grows it is considered aseptic. This usually means that a virus is the cause. Special tests and cultures may or may not identify the virus. Viruses may infect the brain itself causing encephalitis.
Good question. Meningitis is inflammation of the tissues lining the brain and spinal cord. It can be caused by a host of different microorganisms as well as by chemical irritants (introduced by medical procedures), by cancers such as lymphomas, leukemias, etc. The spinal fluid contained in the subarachnoid space formed by the meninges is used to help in determining the cause.