Meningococcal Infection

Introduction And Microbiology

Meningococcal disease is a life-threatening illness caused by Neisseria meningitidis, representing the leading cause of bacterial meningitis in older children and adolescents globally.
Neisseria meningitidis is a fastidious, Gram-negative, aerobic, oxidase-positive, and catalase-positive diplococcus classically appearing kidney-bean shaped.
Optimal growth strictly requires enriched media like chocolate agar or blood agar in an atmosphere of 3% to 5% carbon dioxide.
The organism oxidizes both glucose and maltose, differentiating it from Neisseria gonorrhoeae, which oxidizes only glucose.

Virulence Factor	Mechanism And Clinical Impact
Polysaccharide Capsule	• Serves as the primary virulence factor by inhibiting phagocytosis and complement-mediated lysis. • Classification into 12 serogroups is based on capsular composition, with serogroups A, B, C, W, X, and Y causing almost all invasive disease.
Endotoxin (Lipooligosaccharide)	Triggers a massive cytokine storm (Tumor Necrosis Factor-alpha, Interleukin-1, Interleukin-6) resulting in septic shock, capillary leak, and profound coagulopathy.
Pili And Adhesins (Opa, Opc)	Mediate direct attachment to nasopharyngeal epithelial cells.
IgA1 Protease	Cleaves secretory IgA, facilitating mucosal colonization.

The human nasopharynx remains the sole natural reservoir, with transmission occurring strictly via direct contact with respiratory droplets or saliva.
Asymptomatic carriage peaks in adolescents and young adults (up to 25% to 30%), who serve as the primary reservoir for transmission.
High-risk host factors include
- functional or anatomic asplenia,
- HIV infection,
- the use of eculizumab, and
- specific terminal complement pathway defects (C5–C9) or properdin deficiency, which increase disease risk up to 600-fold.
Pathogenesis involves mucosal colonization, transcytosis across the epithelium into the bloodstream, and rapid multiplication shielded by the capsule.
Release of outer membrane vesicles containing Lipooligosaccharide precipitates widespread endothelial injury, disseminated intravascular coagulation, thrombosis of small vessels, and purpura fulminans.

Clinical Syndrome	Key Clinical Features
Meningococcemia (Septicemia)	Most severe form characterized by rapid progression. Early symptoms include fever, flu-like myalgia, and severe leg pain (a critical early red flag). A blanching maculopapular rash rapidly evolves into non-blanching petechiae and purpura fulminans.
Meningitis	Occurs in 30% to 50% of invasive cases. Presents with fever, headache, photophobia, and nuchal rigidity. Infants manifest subtle signs including a bulging fontanelle, high-pitched cry, and irritability.
Chronic Meningococcemia	A rare form featuring intermittent fever, rash, and arthralgia lasting weeks to months.
Focal Infections	May present as primary or secondary pneumonia, septic or immune-complex arthritis, and purulent pericarditis.

Treatment must never be delayed for diagnostic testing in suspected cases.
Cerebrospinal Fluid Analysis: Reveals polymorphonuclear pleocytosis, elevated protein exceeding 100 mg/dL, and low glucose below 40 mg/dL. Gram stain demonstrates Gram-negative diplococci in 75% to 90% of untreated cases.
Blood And Skin Cultures: Blood culture is positive in 50% to 70% of untreated cases but drops below 5% following antibiotic administration. Gram stain and culture of petechiae or purpura aspirates can remain diagnostic post-antibiotics.
Molecular Testing: Polymerase Chain Reaction targeting meningococcal DNA (e.g., ctrA gene) in blood or cerebrospinal fluid is highly sensitive and remains positive for days after antibiotic treatment.

Antibiotic Agent	Dosage And Role
Ceftriaxone	100 mg/kg/day intravenously once daily or divided every 12 hours (maximum 4g). Serves as the drug of choice because it simultaneously eradicates nasopharyngeal carriage.
Cefotaxime	200 to 300 mg/kg/day intravenously divided every 6 hours. Represents a preferred alternative in neonates.
Penicillin G	300,000 to 400,000 U/kg/day intravenously divided every 4 to 6 hours for susceptible strains. Requires Rifampin prophylaxis before discharge because it fails to eradicate carriage.

Hemodynamic Resuscitation: Aggressive fluid resuscitation utilizing isotonic crystalloids is essential to manage hypovolemia from capillary leak.
Inotropic Support: Vasoactive agents such as epinephrine or dopamine are frequently required to manage myocardial depression and pathological vasodilation.
Adjunctive Corticosteroids: Dexamethasone administered at 0.15 mg/kg every 6 hours is generally recommended if given before or with the first dose of antibiotics to reduce neurologic sequelae like hearing loss.

Indicated strictly for close contacts of the index case within the 7 days preceding illness, administered ideally within 24 hours.
Rifampin: Drug of choice for children, administered orally every 12 hours for 2 days (10 mg/kg for children older than 1 month; 5 mg/kg for neonates).
Ceftriaxone: Single intramuscular dose serving as the drug of choice for pregnant women.
Ciprofloxacin: Single oral dose for adults and children if no local resistance is reported.

Conjugate Vaccines (MenACWY): Induce T-cell dependent immunity, immune memory, and herd immunity by reducing carriage. Routinely administered at 11 to 12 years with a booster at 16 years.
Serogroup B Vaccines (MenB): Recombinant protein vaccines recommended for high-risk groups older than 10 years and during outbreaks.

Case fatality remains high at 5% to 10% despite prompt treatment.
Severe sequelae afflict 11% to 19% of survivors, manifesting as sensorineural hearing loss, limb amputations secondary to purpura fulminans, skin scarring, and permanent neurologic deficits.
Poor prognostic indicators include shock, purpura fulminans, coma, low white blood cell count, and thrombocytopenia.