Meningococcus is a bacterium that can cause meningitis and other forms of meningococcal disease such as meningococcemia, a life–threatening sepsis.
Neisseria meningitidis is a major cause of morbidity and mortality during childhood in industrialized countries and has been responsible for epidemics in Africa and in Asia. Upon Gram staining, it appears as a Gram–negative diplococcus and cultures of the bacteria test positive for the enzyme cytochrome c oxidase.
It exists as normal flora (nonpathogenic) in the nasopharynx of up to 5–15% of adults. It causes the only form of bacterial meningitis known to occur epidemically. Streptococcus pneumoniae (aka pneumococcus) is the most common bacterial etiology of meningitis in children beyond 2 months of age (1–3 per 100,000). Meningococci only infect humans and have never been isolated from animals because the bacterium cannot get iron other than from human sources (transferrin and lactoferrin).
How does it spread?
Meningococcus is spread through the exchange of saliva and other respiratory secretions during activities like coughing, sneezing, kissing, and chewing on toys. It infects the host cell by sticking to it using Trimeric Autotransporter Adhesins (TAA). Those with impaired immunity may be at particular risk of meningococcus (e.g. those with nephrotic syndrome or splenectomy). Vaccines are given in cases of removed or non-functioning spleens.
Signs and Symptoms
Though it initially produces general symptoms like fatigue, it can rapidly progress from fever, headache, and neck stiffness to coma and death. The symptoms of meningitis are easily confused with those caused by other organisms such as Hemophilus influenzae and Streptococcus pneumoniae. Death occurs in approximately 10% of cases.
Suspicion of meningitis is a medical emergency and immediate medical assessment is recommended. Current guidance in the United Kingdom is that if a case of meningococcal meningitis or septicaemia (infection of the blood) is suspected intravenous antibiotics should be given and the ill person admitted to the hospital. This means that laboratory tests may be less likely to confirm the presence of Neisseria meningitidis as the antibiotics will dramatically lower the number of bacteria in the body. The UK guidance is based on the idea that the reduced ability to identify the bacteria is outweighed by reduced chance of death.
Septicaemia caused by Neisseria meningitidis has received much less public attention than meningococcal meningitis even though septicaemia has been linked to infant deaths. Meningococcal septicaemia typically causes a purpuric rash that does not lose its color when pressed with a glass (“non-blanching”) and does not cause the classical symptoms of meningitis. This means the condition may be ignored by those not aware of the significance of the rash. Septicaemia carries an approximate 50% mortality rate over a few hours from initial onset. Many health organizations advise anyone with a non-blanching rash to go to a hospital as soon as possible. Note that not all cases of a purpura–like rash are due to meningococcal septicaemia. However, other possible causes need prompt investigation as well (e.g. ITP a platelet disorder or Henoch-Schönlein purpura).
Other severe complications include:
Waterhouse–Friderichsen syndrome (a massive, usually bilateral, hemorrhage into the adrenal glands caused by fulminant meningococcemia), Adrenal insufficiency, and disseminated intravascular coagulation.