MicrobiologyTier 1Medical Sciences concept

Neisseria meningitidis - clinical presentation and mortality

Core concept

Gram-negative diplococcus, oxidase-positive, ferments maltose and glucose (gonococcus ferments glucose only - "Meningococcus = Maltose")
Polysaccharide capsule defines the serogroup: A, B, C, W, Y, X
- Australia: B and W predominate; W and Y have risen and cause atypical presentations
Carriage is common (~10% of adults, higher in adolescents), invasive disease is rare - the organism crosses the nasopharyngeal epithelium then survives in blood because the capsule resists complement and phagocytosis

Three presentations, three prognoses

Syndrome	Frequency	Mortality
Meningitis alone	~50%	~5%
Meningitis + septicaemia	~40%	Intermediate
Fulminant septicaemia WITHOUT meningitis	~10-20%	~20-40%

Meningococcaemia without meningitis carries the highest mortality - the absence of meningism is a bad sign, not a reassuring one; there has been no time to mount a meningeal response
Waterhouse-Friderichsen syndrome - purpura fulminans + bilateral adrenal haemorrhage + shock

Clinical

Early (first 4-8 h): fever, leg pain, cold hands and feet, abnormal skin colour - present before the rash and before classic meningism
Non-blanching petechial or purpuric rash - may be absent or sparse early, and in ~20% the rash is initially maculopapular
Meningism, photophobia, altered conscious state, seizures
Serogroup W and Y: atypical - pneumonia, septic arthritis, epiglottitis, and a prominent gastrointestinal presentation with diarrhoea that has been repeatedly mistaken for gastroenteritis
Poor prognostic markers: shock without meningitis, rapidly extending purpura, normal or low WCC, normal or low CRP early, thrombocytopenia, coagulopathy, low GCS, absence of meningism

Diagnosis

Blood cultures and blood PCR - PCR remains positive after antibiotics
LP if no contraindication (do not delay antibiotics for it); CSF - neutrophil pleocytosis, high protein, low glucose, Gram-negative diplococci
Do not delay treatment for imaging or LP in suspected meningococcal sepsis

Complications and susceptibility

Amputation, skin grafting, deafness (audiology in all survivors), seizures, cognitive impairment, arthritis, late immune-complex arthritis/vasculitis at day 5-10
Recurrent or unusual-serogroup meningococcal disease -> test terminal complement (CH50, AH50), and consider properdin deficiency and eculizumab exposure
Asplenia and HIV also predispose

Treatment
- Empirical ceftriaxone 2 g IV 12-hourly (or cefotaxime); benzylpenicillin if fully susceptible; add vancomycin and, in the elderly or immunosuppressed, benzylpenicillin for Listeria while the organism is unknown
- Dexamethasone 10 mg IV before or with the first antibiotic dose improves outcome in pneumococcal meningitis and is given empirically; the benefit is not established for meningococcal disease but it is not withheld while the organism is unknown
- Fluid resuscitation, vasopressors, correct coagulopathy
Public health
- Notifiable, immediately, by phone
- Clearance chemoprophylaxis for close household and intimate contacts and for healthcare workers with unprotected airway exposure - ciprofloxacin single dose (or rifampicin, or ceftriaxone in pregnancy)
- The index case also needs clearance therapy unless treated with ceftriaxone
Vaccination (Australian NIP): MenACWY at 12 months and in adolescents (Year 10); MenB funded for Aboriginal and Torres Strait Islander infants, and in South Australia for all infants and adolescents; both MenACWY and MenB for asplenia, complement deficiency, HIV and eculizumab therapy

3 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.