Invasive meningococcal disease occurs when meningococci penetrate the protective mucosal lining of the nasopharynx, resulting in bacteraemia.

N. meningitidis in the blood stream can cause meningitis by crossing the blood-brain barrier. It can also cause overwhelming septicaemia secondary to endotoxin release. In some cases, both processes take place.

It is important to be aware of differences in the pathophysiology of meningitis and septicaemia, as this enables understanding of the differing clinical presentations and subsequent management. Although most patients will have a mixed presentation, it is usually one disease process that predominates.