Neisseria meningitidis and Meningococcal Disease
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Direct answer
Neisseria meningitidis is a Gram-negative, oxidase-positive diplococcus that causes meningitis and meningococcaemia, most often in children and young adults living in close quarters. Its polysaccharide capsule defines the serogroups A, B, C, W, X and Y, which guide vaccine choice. Meningococcal septicaemia with a rapidly spreading purpuric rash is a medical emergency that needs antibiotics before results are available.
What you must remember
- Morphology: Gram-negative kidney-shaped diplococci, often seen inside neutrophils on CSF Gram stain.
- Culture: grows on chocolate agar in carbon dioxide, is oxidase positive, and ferments glucose and maltose but not lactose.
- Serogroups: A, B, C, W, X and Y cause most disease, with serogroup B dominant in many high-income countries and serogroup A linked to epidemic meningitis in the African meningitis belt.
- Meningococcaemia: fever with a petechial or purpuric rash that spreads quickly, sometimes with disseminated intravascular coagulation and shock.
- Waterhouse-Friderichsen syndrome: bilateral adrenal haemorrhage in fulminant septicaemia, causing shock that does not respond to fluid alone.
- Chemoprophylaxis: rifampicin, ciprofloxacin or a single dose of ceftriaxone for close contacts, given as early as possible, ideally within 24 hours.
- Vaccines: conjugate vaccines against serogroups A, C, W and Y, and a separate serogroup B vaccine, chosen according to regional epidemiology.
A stepwise approach to a suspected case
A child presents with fever and a rash that does not fade under pressure from a glass tumbler. The steps below show how the team moves from suspicion to treatment and then to the contacts.
- Recognise the rash: a non-blanching petechial or purpuric rash with fever is meningococcal septicaemia until proven otherwise, and the team does not wait for the child to look more ill.
- Start antibiotics early: a third-generation cephalosporin such as ceftriaxone or cefotaxime is given before results return, and lumbar puncture must not delay the first dose.
- Send samples: blood culture and PCR are taken, and CSF is sampled when it can be done without delaying treatment.
- Watch for adrenal failure: hypotension that does not respond to fluids suggests Waterhouse-Friderichsen syndrome and needs urgent steroid and fluid support.
- Trace the contacts: household members, intimate contacts and close contacts in hostels or daycare receive chemoprophylaxis as early as possible.
- Offer vaccination: serogroup-specific vaccines are offered to contacts and high-risk groups according to national advice.
Where the exam tries to catch you
Meningococcal questions often hinge on a single detail in the rash, the sugar reaction or the timing of treatment.
- Trap: confusing N. meningitidis with N. gonorrhoeae because both are Gram-negative diplococci Correct: N. meningitidis ferments maltose, whereas N. gonorrhoeae ferments only glucose, and both are oxidase positive.
- Trap: delaying antibiotics for a lumbar puncture in a child with purpura Correct: the first antibiotic dose should not wait, because meningococcal septicaemia can progress to death within hours.
- Trap: treating a rash as benign because the child looks well Correct: a non-blanching rash with fever is an emergency, and early disease can look deceptively mild.
Frequently asked questions
Which serogroups of Neisseria meningitidis cause most disease?
Serogroups A, B, C, W, X and Y cause most meningococcal disease. Serogroup B dominates in many high-income countries, while serogroup A has caused epidemic meningitis in the African meningitis belt, so vaccine choice follows regional serogroup patterns.
What is Waterhouse-Friderichsen syndrome in meningococcal disease?
Waterhouse-Friderichsen syndrome is bilateral adrenal haemorrhage that occurs in fulminant meningococcal septicaemia. It causes profound shock that does not respond to fluid alone, and it needs urgent steroid and fluid support.
Who should receive chemoprophylaxis after a case of meningococcal disease?
Household members, intimate contacts and close contacts in hostels or daycare should receive chemoprophylaxis after a case of meningococcal disease. Rifampicin, ciprofloxacin or a single dose of ceftriaxone are the usual options, and they are given as early as possible.
How is Neisseria meningitidis differentiated from Neisseria gonorrhoeae?
Neisseria meningitidis is differentiated from Neisseria gonorrhoeae by its ability to ferment maltose, which gonococci cannot do. Both are oxidase-positive Gram-negative diplococci, so the sugar reaction and the clinical context guide identification.
What does a Gram stain of CSF showing diplococci inside neutrophils suggest?
Gram-negative diplococci inside neutrophils on a CSF Gram stain suggest Neisseria meningitidis meningitis. The finding is not always present, so PCR and culture are needed to confirm the diagnosis.