Humans are the only known reservoir for Neisseria meningitidis (also known as the meningococcus). Around 10% of the population carries the meningococcus in the back of their throat or nose without causing any illness. It is transmitted from person to person by inhaling respiratory secretions from the mouth and throat or by direct contact (kissing). Close and prolonged contact is usually needed for transmission.
Occasionally, the meningococcus can cause invasive disease, including meningitis (inflammation of the meninges), septicaemia (blood poisoning) and pneumonia. Young children and teenagers are at highest risk of meningococcal disease. It is not known why some individuals carry the bacteria without them causing harm while others go on to develop invasive disease.
Early signs and symptoms of meningococcal disease may be non-specific and, therefore, difficult to distinguish from common and self-limiting viral illnesses. More detailed information on the symptoms of meningococcal disease is available on the Meningitis Research Foundation and Meningitis Now web sites.
Laboratories that diagnose a case of meningococcal infection should refer all cases for further characterisation at the Meningococcal Reference Unit (MRU). Serogrouping is important to inform the subsequent management of case contacts, while strain differentiation and genotyping are useful for investigation of potentially linked cases and outbreaks.