What causes meningococcal meningitis?

Updated: Jul 16, 2018
  • Author: Francisco de Assis Aquino Gondim, MD, PhD, MSc, FAAN; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Individuals acquire meningococcal infections if they are exposed to virulent bacteria and have no protective bactericidal antibodies.

The natural habitat and reservoir for meningococci is the mucosal surfaces of the human nasopharynx and, to a lesser extent, the urogenital tract and anal canal. Approximately 5-10% of adults are asymptomatic nasopharyngeal carriers, but that number increases to as many as 60-80% of members of closed populations (eg, military recruits in camps).

The modes of infection include direct contact or respiratory droplets from the nose and throat of infected people. Meningococcal disease most likely occurs within a few days of acquisition of a new strain, before the development of specific serum antibodies.

The incubation period averages 3-4 days (range 1-10 days), which is the period of communicability. Bacteria can be found for 2-4 days in the nose and pharynx and for up to 24 hours after starting antibiotics. Treatment with penicillin may not eradicate the bacteria from the nasopharyngeal carriers.

After adherence to the nasopharyngeal mucosa, meningococci are transported to membrane-bound phagocytic vacuoles. Within 24 hours, they can be seen in the submucosa, close to vessels and local immune cells. In most cases, meningococcal colonization of mucosal surfaces leads to subclinical infection or mild symptoms.

In approximately 10-20% of cases, N meningitidis enters the bloodstream. In the vascular compartment, the bacterium may be killed by bactericidal antibodies, complement, and phagocytic cells, or it may multiply, initiating the bacteremic phase. Organisms replicate rapidly.

Systemic disease appears with the development of meningococcemia and usually precedes meningitis by 24-48 hours. This can lead to systemic infection in the form of bacteremia, metastatic infection that commonly involves the meninges, or severe systemic infection with circulatory collapse and DIC. Meningococcemia leads to diffuse vascular injury, which is characterized by endothelial necrosis, intraluminal thrombosis, and perivascular hemorrhage.

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