Meningococcal infection is a life-threatening disease with a short incubation period and rapid progression caused by Neisseria meningitidis. Approximately half of all cases of invasive meningococcal disease are associated with meningitis, but counter-intuitively, those patients with meningococcemia sparing the central nervous system often have more severe illness.  Almost all human infections are caused by N. meningitidis serogroups A, B, C, Y, and W-135. Vaccines directed against serogroups A, C, Y, and W-135 have been available since the 1970s, while vaccines to prevent serogroup B disease first became available in 2014. Serogroup X also deserves special mention as a bacterial type that has emerged as a cause of outbreaks in parts of Africa. To date, a vaccine against serogroup X is not available.

The first symptoms of invasive meningococcal infection are nonspecific, usually including fever and a general sense of feeling unwell. The possibility that an ill-appearing patient may have meningococcemia may only first be considered when symptoms of meningitis become evident (photophobia, headache, and stiff neck), or when the patient develops a petechial or purpuric rash.  Such symptoms usually manifest within 12–24 hours of fever onset. Because meningococcal infection can progress in a fulminant manner, every clinician should treat symptoms of meningitis, or fever with petechiae as medical emergencies. The diagnosis is fairly straightforward, but treatment with parenteral antibiotics should not be delayed while awaiting microbiologic confirmation of the clinical diagnosis.

For patients who have yet to receive antibiotic treatment, a standard blood culture will usually reveal the organism in a day or two. Patients with clinical manifestations suggesting meningitis should undergo lumbar puncture. Cerebrospinal fluid (CSF) culture will usually identify the organism, but preliminary evidence of bacterial meningitis is suggested by a pleocytosis (predominantly neutrophils) and a biochemical profile showing low CSF glucose, and elevated protein concentration.  A gram stain of the fluid may show the characteristic gram negative diplococci.