Meningococcal disease is an acute, potentially severe illness caused by the bacterium Neisseria meningitidis. N. meningitidis, or meningococcus, is an aerobic, gram-negative diplococcus, closely related to N. gonorrhoeae. Almost all invasive disease is caused by one of five serogroups: A, B, C, Y, and W. Neisseria meningitidis is a leading cause of bacterial meningitis and sepsis. It can also cause focal disease, such as pneumonia and arthritis.
It is passed on by breathing in droplets in the air from infected people. The incubation period of meningococcal disease is 3–4 days, with a range of 2–10 days. Early signs of the illness are weakness, fever and sickness, sometimes followed by headache, discomfort when seeing bright light, feeling sleepy, confusion, painful joints and a rash. Those infected can end up unconscious. If untreated, meningitis can lead to death. Meningitis is the most common presentation of invasive meningococcal disease. Less common presentations of meningococcal disease include pneumonia (5%–15% of cases), arthritis (2%), otitis media (1%), and epiglottitis (less than 1%).
The case-fatality rate of invasive meningococcal disease is 9%–12%, even with appropriate antibiotic therapy. The fatality rate of meningococcemia is up to 40%. As many as 20% of survivors have permanent sequelae, such as hearing loss, neurologic damage, or loss of a limb.
Family members of an infected person are at increased risk for meningococcal disease. Antecedent upper respiratory tract infection, household crowding, and both active and passive smoking are also associated with increased risk. During outbreaks, bar or nightclub patronage and alcohol use have also been associated with higher risk for disease.
Invasive meningococcal disease is typically diagnosed by isolation of N. meningitidis from a normally sterile site.