Meningitis is an inflammation of the Pia mater and the arachnoid mater. The inflammation may be caused by infection with bacteria, viruses or other microorganisms. Meningitis is seen a lot in children and adolescents. Approx. 70 % of the cases are seen in children under the age of 5. The incidence is highest in the first two years of life. While meningitis is a relatively rare disease in highly developed countries, it is very common in developing countries.