DIAGNOSIS OF INVASIVE NEISSERIA MENINGITIDIS INFECTIONS. Invasive meningococcal infections are unpredictable, difficult to diagnose and extremely serious, with a high risk of death and sequelae in survivors. They primarily affect subjects with no underlying pathology, but risk factors have been identified. The most frequent clinical forms are meningitis, septicemia and meningococcal septic shock, including purpura fulminans. Atypical presentations, such as pneumonia, epiglottitis and digestive tract infections, are increasingly common, especially since the incidence of serogroups W and Y has risen. They can lead to misdiagnosis and are associated with higher case-fatality rates.