Based on reactions with antisera, different polysaccharides have been identified as so-called serogroups, classifying at least 13 serogroups. Other serogroups are of little importance. Most people may have carried potentially harmful meningococci in the throat for some time. Such carriage is usually harmless, but on rare occasions the meningococci invade the blood and cause disease.
Meningococcal disease has two main manifestations, meningitis and septicaemia.
Meningitis is an inflammation of the lining of the brain and spinal chord and can lead to rapid death or permanent brain damage, particularly in young children. Five to ten percent of those suffering from this manifestation of the disease die as a result of it. The most common symptoms of meningococcal meningitis are vomiting, severe headache, a stiff neck and abnormal sensitivity to light. In infants and small children high fever, irritability and vomiting are often the only signs, and children are frequently not brought to the hospital until loss of consciousness or convulsions occur. If the blood is infected, the patient often experiences generalised malaise, headache, weakness and hypotension.