Two major meningococcal infections (meningitis and meningococcemia) are usually caused by the gram-negative bacteria Neisseria meningitidis, which also causes primary pneumonia, purulent conjunctivitis, endocarditis, sinusitis, and genital infection.
Meningococcemia occurs as simple bacteremia, fulminant meningococcemia and, rarely, chronic meningococcemia. It commonly accompanies meningitis. (For more information on meningitis, see “Meningitis,” pages 517 to 520.) Meningococcal infections may occur sporadically or in epidemics; virulent infections may be fatal within a matter of hours.
Meningococcal infections are most common among children (ages 6 months to 1 year) and men, usually military recruits, because of overcrowding.
Streptococcus pneumoniae and N. meningitidis are the leading causes of meningococcal infections. N. meningitidis has seven serogroups (A, B, C, D, X, Y, and Z); group A causes most epidemics. These bacteria are commonly present in upper respiratory flora. Transmission takes place through inhalation of an infected droplet from a carrier (2% to 38% of the population). The bacteria then localize in the nasopharynx.
Following an incubation period of 3 to 4 days, the bacteria spread through the bloodstream to the joints, skin, adrenal glands, lungs, and central nervous system. The tissue damage that results (possibly due to the effects of bacterial endotoxins) produces symptoms and, with fulminant meningococcemia and meningococcal bacteremia, progresses to hemorrhage, thrombosis, and necrosis.