Neisseria meningitidis

Neisseria meningitidis (the meningococcus)

Organism

Neisseria meningitidis is a gram-negative diplococcus, typically flattened where the cocci meet.
Aerobic (def).
There are 13 serogroups of meningococci. Serogroups B and C commonly cause meningitis (def) and meningococcemia (def) in developed countries; serogroups Y and W135 typically cause pneumonia.

Habitat

Humans are the only natural host.

Source

Transmitted person-to-person by aerosolized respiratory tract secretions.

Clinical Disease

There are between 2000 and 3000 cases of meningococcal meningitis per year in the U.S. A total of 2725 cases were reported to CDC in 1998.
N. meningitidis infects the nasopharynx of humans causing a usually mild or subclinical upper respiratory infection. However in about 15% of these individuals, the organism invades the blood and disseminates, causing septicemia and from the there may cross the blood-brain barrier causing meningitis (def). A petechial skin rash, caused by endotoxin in the blood, appears in about 75 percent of the septic cases and fatality rates for meningococcal septicemia are as high as 30 percent as a result of the shock cascade. A fulminating form of the disease, called Waterhouse-Frederichsen syndrome, can be fatal within several hours due to massive intravascular coagulation and resulting shock, probably a result of massive endotoxin release. N. meningitidis is especially dangerous in young children.
Typical symptoms are headache, meningeal signs, and fever.
Mortality is close to 100% if untreated; less than 10% with prompt and appropriate antibiotic therapy.

From Meningococcal Infections, by Thomas A Hoffman, MD, Professor, Department of Internal Medicine, Division of Infectious Diseases, Jackson Memorial Hospital, University of Miami.