Neisseria Meningitidis — Meningococcal Meningitis

Pathogenic mechanisms of meningococcal infection

• Mucosal colonization and invasion: N. meningitidis expresses pili (fimbriae) for epithelial attachment and opacity proteins (Opa and Opc) for cellular tropism. The bacterium crosses the nasopharyngeal mucosa via transcytosis through epithelial cells or paracellularly through disrupted tight junctions. Polysaccharide capsule variants (serogroups A, B, C, W, Y, X) determine invasiveness; certain strains (e.g., serogroup B) possess capsules with reduced immunogenicity due to molecular mimicry of neural tissue.

• Blood-brain barrier (BBB) penetration and CNS inflammation: Once bacteremia develops, meningococci cross the BBB through multiple mechanisms: direct endothelial invasion via TspA and NadA adhesins, paracellular leakage from complement-mediated endothelial injury, and transcytosis via gp96 receptor interaction. Bacterial lipopolysaccharide (LPS), lipooligosaccharide (LOS), and peptidoglycans trigger robust innate immune responses through TLR4, TLR2, and other pattern recognition receptors. This stimulates release of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-8) from resident microglia, astrocytes, and infiltrating leukocytes, creating a feed-forward inflammatory cascade that damages the meninges and cortex.

• Meningeal inflammation and complications: Intense leukocytic infiltration (initially neutrophils, later lymphocytes) into the subarachnoid space generates purulent exudate. Inflammatory mediators increase capillary permeability, causing cerebral edema (vasogenic and cytotoxic), elevated intracranial pressure (ICP), and impaired cerebral perfusion. Bacterial autolysins and immune lysis release additional LOS, perpetuating inflammation even after antimicrobial killing. Vasculitis from direct bacterial invasion or immune complex deposition can damage cortical vessels, causing stroke (particularly in distribution of middle cerebral artery). Subdural effusions develop from inflammatory exudate accumulation between dura and arachnoid. In fulminant sepsis, disseminated intravascular coagulation (DIC) with protein C and protein S deficiency drives thrombotic microvasculature occlusion and tissue necrosis, classically manifested as petechial or purpuric rash with rapid progression to gangrene (Waterhouse-Friderichsen syndrome).

Primary pathogen

• Neisseria meningitidis — gram-negative diplococci, oxidase-positive, ferments glucose and maltose, catalase-positive; facultative intracellular organism with 13 serogroups (A, B, C, W-135, Y, X most clinically relevant)

Risk factors for invasive meningococcal disease

• Asplenia (anatomic or functional, including sickle cell disease) — loss of opsonizing antibodies and alternative complement pathway activation; 50-fold increased risk
• Complement deficiencies (C5-C9 terminal pathway, C3, Factor H, Factor D, Factor B, Properdin) — inability to form membrane attack complex; accounts for ~5-10% of meningococcal meningitis
• Respiratory tract infection — recent URI or pneumonia increases mucosal invasion
• Close contact exposure — household members, dormitory residents, military recruits; secondary attack rate ~500-1000 per 100,000 population
• Age extremes — infants <5 years (peak <2 years) and adolescents/young adults 15-24 years; second peak due to waning immunity and increased respiratory exposure
• Immunocompromise — HIV/AIDS (especially CD4 <200), malignancy, immunosuppressive medications
• Antecedent viral infection — influenza, measles; alters mucosal immunity and increases secondary bacterial invasion
• Tobacco smoke exposure — impairs mucociliary clearance and innate immunity
• Laboratory diagnosis of meningococcemia without meningitis — hyperacute presentation may precede CNS involvement
• Anatomic abnormalities — CSF leak, ventriculoperitoneal shunt, recent neurosurgery, basilar skull fracture

Acute meningitis syndrome (typical presentation)

• Classic triad — fever (>38.5°C), headache, and nuchal rigidity (neck stiffness); however, absent in 50% of cases, limiting diagnostic sensitivity
• Fever — sudden onset, high fever characteristic of bacterial meningitis; present in >90% of cases
• Headache — severe, frontal or generalized; often resistant to analgesics; worsened by neck flexion
• Altered mental status — ranging from confusion and delirium to lethargy and coma; progresses rapidly over hours; present in 20-30% at presentation, up to 80% during course
• Photophobia — light sensitivity with pain on eye opening; present in ~50% of meningitis cases
• Nausea and vomiting — non-bilious, from meningeal irritation and increased ICP

Physical examination findings

• Nuchal rigidity — inability to passively flex neck due to meningeal irritation; check by passive neck flexion with patient supine
• Kernig sign — pain and resistance with hip at 90° and knee extension (less sensitive, ~5-10%)
• Brudzinski sign — involuntary hip/knee flexion when patient's neck is passively flexed; low sensitivity (~5%) but highly specific
• Petechial or purpuric rash — hallmark of meningococcemia; appears in 50-80% of meningococcal disease but only 10-15% of meningococcal meningitis (more common in sepsis presentations). Rash is non-blanching, begins on extremities and trunk, may rapidly progress to large purpuric patches or black necrotic areas (gangrene). Absence does NOT exclude meningococcal disease
• Altered level of consciousness — ranging from drowsiness to deep coma; indicates severe disease
• Seizures — occur in 20-40% of meningitis cases; may be generalized or focal; later sign indicating cortical involvement or elevated ICP
• Focal neurologic deficits — cranial nerve palsies (CN III, VI, VII most common from increased ICP), hemiparesis, aphasia; indicate vasculitis or stroke

Fulminant meningococcemia (sepsis without prominent meningitis)

• Rapid progression — deterioration within 6-12 hours to septic shock
• Purpuric or petechial rash — rapidly progressive, often becomes widespread and confluent; classic "doesn't blanch with pressure" finding
• Shock — hypotension, tachycardia, cold extremities, poor perfusion; reflects DIC and endotoxemia
• Multi-organ dysfunction — acute respiratory distress syndrome (ARDS), acute kidney injury, hepatic dysfunction, myocarditis
• Waterhouse-Friderichsen syndrome — acute adrenal insufficiency from bilateral adrenal hemorrhage and necrosis (occurs in ~5% of fulminant meningococcemia); presents with shock refractory to fluids and vasopressors, often with purpura fulminans

Meningitis without sepsis (less common, ~20-30% of cases)

• Absence of bacteremia on blood cultures
• Absence of rash
• More indolent presentation with slower progression

Clinical suspicion triggers

• Acute fever with headache and nuchal rigidity (classic triad)
• Fever with petechial/purpuric rash in any patient, especially young adult
• Fever with altered mental status and rapid clinical deterioration
• Any case of acute meningitis with rash

Laboratory evaluation

• Cerebrospinal fluid (CSF) analysis via lumbar puncture (LP) — GOLD STANDARD
• Appearance: Turbid, milky, or frankly purulent (cloudy)
• Cell count: 1000-10,000 WBC/μL (range 100-50,000); predominantly neutrophilic (>80% PMN in most cases); early infection may show lymphocytic predominance
• Protein: 100-1000 mg/dL (markedly elevated; typical 400-600 mg/dL)
• Glucose: Low with markedly reduced CSF:serum glucose ratio (<0.4 or absolute <40 mg/dL); CSF glucose lower than serum (normal ratio >0.5)
• Gram stain: Gram-negative diplococci (kidney bean-shaped) in 50-60% of untreated cases; sensitivity decreases to ~30% if patient received prior antibiotics
• Bacterial culture: Positive in 70-90% of untreated meningitis; remains positive even with pre-treatment antibiotics in most cases; MOST IMPORTANT for organism identification and antibiotic susceptibilities
• PCR (polymerase chain reaction): Real-time PCR for 16S rRNA and meningococcal-specific genes; sensitivity 90-95%, specificity >95%; increasingly available and rapidly identifies organism even with prior antibiotics
• Latex agglutination or immunofixation: Detects meningococcal capsular antigen; ~60-70% sensitivity in untreated cases; less often used now with PCR availability

• Blood cultures — obtain BEFORE antibiotics if possible
• Positive in 50-70% of meningococcal meningitis
• Critical for organism identification and susceptibility testing
• Meningococcemia often bacteremic even without meningitis

• Complete blood count (CBC):
• Leukocytosis — WBC 10,000-30,000/μL typical (can be >50,000 in fulminant disease); left shift with immature forms
• Thrombocytopenia — in sepsis/DIC presentations (platelet count <100,000/μL); prognostic indicator of worse outcome
• Anemia — from hemolysis or acute disease

• Coagulation studies:
• PT/INR, PTT prolonged — in DIC
• Fibrinogen low — in DIC
• D-dimer elevated — indicates thrombosis/DIC
• Protein C, Protein S low — in fulminant disease

• Blood glucose — ESSENTIAL for interpreting CSF glucose (need serum glucose for ratio calculation)

• Serum procalcitonin — elevated in bacterial meningitis; helps differentiate from viral; not routinely necessary for diagnosis but supportive

• Lactate (serum or CSF) — elevated in bacterial meningitis; CSF lactate >4 mmol/L suggests bacterial infection

Imaging evaluation

• CT head (before LP if meningitis suspected) — ONLY if contraindications to LP present
• Indications for CT before LP: Papilledema on exam, focal neurologic deficits (except CN palsies), immunocompromise, mass lesion concern, decreased level of consciousness, signs of increased ICP
• Findings: Usually normal in uncomplicated meningitis; may show cerebral edema, subdural effusions, infarction, or hemorrhage in complicated cases
• Note: Normal CT does NOT exclude meningitis; meningitis can be severe with normal imaging

• MRI brain (after stabilization) — superior to CT for meningeal enhancement and complications
• Typical findings: Diffuse leptomeningeal enhancement (basal cisterns, sulci, fissures) on gadolinium-enhanced T1 sequences; T2/FLAIR hyperintensity in subarachnoid spaces
• Complications: Subdural effusions, ventriculitis (enhancement of ventricular ependyma), infarction, hemorrhage, abscess (rare)
• Timing: Not emergent; obtain after stabilization if clinically indicated

Diagnostic approach/algorithm

1. 1.Clinical suspicion of meningitis → Immediate treatment does NOT wait for diagnostic confirmation
2. 2.Blood cultures (at least 2 sets)
3. 3.Empiric antibiotics immediately (within 1 hour of symptom recognition)
4. 4.Lumbar puncture (if no contraindications) within 30 minutes of presentation

• If LP delayed, obtain CT head first; do not delay antibiotics

1. 1.CSF analysis: Gram stain, culture, PCR, chemistry, cell count
2. 2.MRI brain after stabilization if complications suspected

Diagnostic criteria (meningitis confirmed if)

• Positive CSF culture (gold standard) OR
• Positive CSF Gram stain showing gram-negative diplococci compatible with meningococcus OR
• Positive CSF PCR/molecular assay for N. meningitidis OR
• Positive blood culture with meningitis clinical syndrome (counts as meningococcal meningitis) OR
• Meningococcal polysaccharide antigen in CSF by immunofixation

EMERGENT measures (before culture results/identification)

• Immediate empiric antibiotics — DO NOT DELAY for LP or imaging; administer within 1 hour of recognition
• Empiric broad-spectrum coverage must include N. meningitidis:
• First-line: Ceftriaxone 2 g IV Q12H (4 g total daily dose for meningitis dosing; higher doses than non-meningitis infections due to CSF penetration and meningococcal resistance concerns)
• Alternative if cephalosporin allergy: Moxifloxacin 400 mg IV Q24H or chloramphenicol 1 g IV Q6H (chloramphenicol less preferred now)
• If suspected meningococcal meningitis with PCN allergy and normal renal function: Use moxifloxacin (fluoroquinolones penetrate CSF well)

Definitive antibiotic therapy (once N. meningitidis confirmed)

• Ceftriaxone 2 g IV Q12H × 7-10 days — beta-lactam with excellent CSF penetration; first-line for all meningococcal susceptibilities
• Cefotaxime 2 g IV Q4-6H — alternative to ceftriaxone; equivalent efficacy
• Penicillin G 4 million units IV Q4H × 7-10 days — historically standard; now only if susceptible (most meningococci now have elevated penicillin MICs)
• Penicillin-susceptible meningococcus (MIC ≤0.06 μg/mL): Penicillin G or ceftriaxone acceptable
• Penicillin-intermediate meningococcus (MIC 0.12-1 μg/mL): Ceftriaxone preferred
• Penicillin-resistant meningococcus (MIC ≥2 μg/mL): Ceftriaxone mandatory; very rare in most developed countries

• Chloramphenicol 1 g IV Q6H — alternative if severe cephalosporin allergy (caution

Neurologic complications (mechanism → signal)

• Cerebral edema with herniation — EMERGENCY. Cytokine-driven vasogenic plus cytotoxic edema raises ICP; signaled by declining GCS, unilateral fixed pupil, posturing, or Cushing reflex (hypertension with bradycardia). Requires airway control, head elevation, hyperosmolar therapy, and neurosurgical/ICU involvement; a lumbar puncture in this setting can precipitate herniation, which is why IDSA lists depressed consciousness, focal deficits, and papilledema as pre-LP CT indications.
• Seizures and status epilepticus — EMERGENCY. Cortical irritation from purulent exudate or infarction; new focal seizure after day 3 suggests venous or arterial infarct.
• Cerebral vasculitis/arterial or venous infarction — inflamed cortical vessels thrombose; signaled by hemiparesis or aphasia with restricted diffusion on MRI.
• Sensorineural hearing loss — the single most common sequela; suppurative labyrinthitis via the cochlear aqueduct. Every survivor needs formal audiometry before or shortly after discharge (AAP/IDSA practice).
• Hydrocephalus, subdural effusion, subdural empyema, ventriculitis — exudate obstructs arachnoid granulations or loculates; suspect with persistent fever, vomiting, or bulging fontanelle, and image.
• SIADH-related hyponatremia — excessive ADH from meningeal inflammation; falling sodium with concentrated urine worsens edema.

Systemic complications

• DIC / purpura fulminans — EMERGENCY. Endotoxin-driven tissue factor expression with acquired protein C/S depletion; expanding non-blanching purpura, falling platelets and fibrinogen, rising D-dimer. Leads to digital/limb gangrene and amputation.
• Waterhouse–Friderichsen syndrome — bilateral adrenal hemorrhage; EMERGENCY signaled by catecholamine-refractory shock, hypoglycemia, hyperkalemia. Give stress-dose hydrocortisone empirically, consistent with Surviving Sepsis Campaign guidance on refractory shock.
• Immune-complex arthritis, pericarditis, or vasculitic rash appearing around days 4–7 despite sterile cultures — treat with NSAIDs, not antibiotic escalation.

Treatment-related

• Ceftriaxone: biliary pseudolithiasis, drug fever, C. difficile colitis; avoid with calcium-containing infusions in neonates.
• Chloramphenicol: dose-related marrow suppression, idiosyncratic aplastic anemia, gray baby syndrome.
• Rifampin prophylaxis: orange body fluids and CYP induction that defeats oral contraceptives.

• Buzzword microbiology: gram-negative kidney bean–shaped diplococci on CSF Gram stain; N. meningitidis ferments maltose AND glucose, whereas N. gonorrhoeae ferments glucose only. Oxidase-positive; CSF and blood isolates grow on chocolate/blood agar, while modified Thayer–Martin is the selective medium reserved for contaminated specimens such as nasopharyngeal carriage swabs. The polysaccharide capsule is the key virulence factor.
• Single best next step in a febrile patient with a non-blanching petechial rash: draw blood cultures and give IV ceftriaxone immediately — never delay antibiotics for CT or LP. In adults, empiric therapy also covers pneumococcus (add vancomycin, dosed to a 24-hour AUC/MIC of 400–600 per the 2020 IDSA/ASHP consensus) and, if over age 50 or immunocompromised, ampicillin for Listeria.
• The association examiners love: recurrent Neisseria infections = terminal complement deficiency (C5–C9) or properdin deficiency. Screen with CH50 (total hemolytic complement). Complement inhibitors (eculizumab, ravulizumab) carry a boxed warning for meningococcal disease and mandate vaccination before use.
• Dexamethasone nuance: IDSA supports adjunctive dexamethasone given with or just before the first antibiotic dose when pneumococcal meningitis is suspected; proven benefit in meningococcal disease is not established, and it is typically stopped once N. meningitidis is identified.
• Chemoprophylaxis is a favorite stem: household/childcare contacts, intimate partners, and anyone exposed to respiratory secretions (mouth-to-mouth, intubation without a mask) get rifampin, ciprofloxacin, or IM ceftriaxone — the CDC-preferred option in pregnancy. Where ciprofloxacin-resistant isolates have been documented, CDC endorses azithromycin 500 mg PO ×1 as an alternative. Casual classroom or hospital-ward contact does not qualify.
• Isolation: droplet precautions for the first 24 hours of effective therapy.
• Vaccination (ACIP) — keep the two products separate:
• MenACWY: routine at 11–12 years with a booster at 16; also for asplenia, persistent complement deficiency or complement-inhibitor use, HIV, microbiologists routinely handling N. meningitidis, military recruits, and travel to the African meningitis belt or the Hajj (a Saudi entry requirement).
• MenB: shared clinical decision-making at 16–23 years; recommended for asplenia, persistent complement deficiency or complement-inhibitor use, microbiologists, and serogroup B outbreak control — not for routine travel. A pentavalent MenABCWY product may be used when both are due at the same visit.
• Distractors to avoid: absence of rash does not exclude meningococcal disease; Kernig and Brudzinski signs are specific but insensitive, so their absence proves nothing. Also, a patient treated with penicillin or chloramphenicol still needs carriage-eradicating prophylaxis before discharge, while ceftriaxone therapy already clears nasopharyngeal carriage.