With the advent and implementation of vaccinations for organisms such as Streptococcus pneumoniae, Haemophilus influenza type B, and Neisseria meningitis, rates of bacterial meningitis have been in decline, making viral meningitis more common. Countries without high rates of immunization still carry higher rates of bacterial disease. While the disease can occur in both children and adults, it is more common in children. Rates of infection tend to reach a peak in the summer and fall. During an outbreak in Romania and in Spain viral meningitis was more common among adults. While, people aged younger than 15 made up 33.8% of cases. In contrast in Finland in 1966 and in Cyprus in 1996, Gaza 1997, China 1998 and Taiwan 1998, the incidence of viral meningitis was higher among children. Recent research
It has been proposed that viral meningitis might lead to inflammatory injury of the vertebral artery wall.The Meningitis Research Foundation is conducting a study to see if new genomic techniques can improve the speed, accuracy and cost of diagnosing meningitis in children in the UK. The research team will develop a new method to be used for the diagnosis of meningitis, analysing the genetic material of microorganisms found in CSF (cerebrospinal fluid). The new method will first be developed using CSF samples where the microorganism is known, but then will be applied to CSF samples where the microorganism is unknown (estimated at around 40%) to try and identify a cause.
In meningitis, the barrier is disrupted, so once viruses have entered the brain, they are isolated from the immune system and can spread. This leads to elevated intracranial pressure, cerebral edema, meningeal irritation, and neuronal death. Diagnosis
The diagnosis of viral meningitis is made by clinical history, physical exam, and several diagnostic tests. Kernig and Brudzinski signs may be elucidated with specific physical exam maneuvers, and can help diagnose meningitis at the bedside. Most importantly however, cerebrospinal fluid (CSF) is collected via lumbar puncture (also known as spinal tap). This fluid, which normally surrounds the brain and spinal cord, is then analyzed for signs of infection. CSF findings that suggest a viral cause of meningitis include an elevated white blood cell count (usually 10-100  cells/µL) with a lymphocytic predominance in combination with a normal glucose level. Increasingly,  cerebrospinal fluid PCR tests have become especially useful for diagnosing viral meningitis, with an estimated sensitivity of 95-100%. Additionally, samples from the stool, urine, blood and throat can also help to identify viral meningitis. CSF vs serum c-reactive protein and procalcitonin have not been shown to elucidate whether meningitis is bacterial or viral.In certain cases, a CT scan of the head should be done before a lumbar puncture such as in those with poor immune function or those with increased intracranial pressure.