London, July 1 (IANS): Viruses are the most common cause of meningitis in adults and a cause of substantial long-term ill health in Britain, says a study.

Meningitis is an acute inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges.

Diagnosis of meningitis is often delayed due to unnecessary brain scans being performed before lumbar puncture -- which is the essential investigation to determine the cause of the illness, said the study published in the The Lancet Infectious Diseases journal.

"It (the study) shows that viral meningitis is now a major cause of meningitis, but often the management is not quite right. It's a concerning finding that so many unnecessary brain scans are taking place and that these appear to be delaying the correct diagnosis," said co-author Fiona McGill from the University of Liverpool.

For the study, the researchers studied the diagnosis and treatment of more than 1,000 patients with suspected meningitis.

The majority of patients (81 per cent) had a brain scan and 70 per cent of those took place before lumbar puncture, otherwise known as a spinal tap.

The researchers found that patients who were investigated promptly with lumbar puncture were also more likely to have a specific cause of meningitis identified and to spend less time in a hospital.

They also found that overall, the specific virus or bacteria causing the illness was not identified for 43 per cent of patients.

Being able to quickly determine which bacteria or virus is causing the illness is essential for the appropriate treatment of patients, the researchers noted.