A 28-year-old woman from Delhi presents with recurrent Neisseria meningitidis meningitis (third episode in 2 years). Routine investigations show normal immunoglobulin levels and normal neutrophil function. Serum complement levels are pending. What is the most appropriate immediate next step in management?

Explanation

## Clinical Context A 28-year-old woman with **three episodes of Neisseria meningitidis meningitis in 2 years**, normal immunoglobulin levels, and normal neutrophil function is presenting in a **stable, inter-episode (outpatient) state** — the stem does not describe acute fever, neck stiffness, or altered sensorium. This pattern of recurrent meningococcal disease is the classic hallmark of **terminal complement deficiency (C5–C9 / Membrane Attack Complex deficiency)**. ## Why Option B Is the Immediate Next Step **Key Point:** When a patient with recurrent meningococcal disease presents in a stable, non-acute state, the *immediate* priority is: 1. **Prophylaxis of close contacts** with rifampicin (600 mg BD × 2 days in adults) to eliminate nasopharyngeal carriage and prevent secondary cases. 2. **Meningococcal vaccination of the patient** — both MenACWY (conjugate) and serogroup B vaccine (Bexsero). Complement-deficient patients carry a **≥1000-fold higher lifetime risk** of invasive meningococcal disease and must be vaccinated regardless of pending complement results. These interventions are **not deferred** pending laboratory confirmation — they are standard-of-care public health and preventive measures that must be initiated immediately (Harrison's Principles of Internal Medicine, 21st ed., Chapter on Meningococcal Infections; CDC Meningococcal Vaccination Guidelines). ## Why Each Distractor Is Wrong | Option | Reason | |--------|--------| | **A: Empiric ceftriaxone + vancomycin** | Appropriate during *acute* bacterial meningitis. This patient is currently **stable and afebrile** (inter-episode presentation). Empiric antibiotics are not indicated in the absence of acute illness. | | **C: Flow cytometry for CD55/CD59** | CD55 (DAF) and CD59 (protectin) are GPI-anchored complement regulators whose absence defines **Paroxysmal Nocturnal Hemoglobinuria (PNH)** — a clonal stem cell disorder causing complement-mediated *intravascular hemolysis*, thrombosis, and cytopenias. PNH does **not** cause susceptibility to recurrent Neisseria infections. Terminal complement deficiency (C5–C9) is a distinct entity tested by CH50/AH50, not CD55/CD59 flow cytometry. | | **D: High-dose IVIG** | IVIG replaces or supplements *immunoglobulins* and is indicated for **antibody deficiencies** (e.g., hypogammaglobulinemia, XLA, CVID). This patient has **normal immunoglobulin levels**; her defect is in the complement system, not humoral immunity. IVIG has no role in complement deficiency. | ## Subsequent Workup (After Immediate Prophylaxis + Vaccination) 1. **CH50 (total hemolytic complement):** Screens for classical pathway + MAC deficiency; will be markedly low or absent in C5–C9 deficiency. 2. **AH50:** Screens alternative pathway. 3. **Individual complement components (C5–C9):** To identify the specific deficient protein. 4. **Family screening:** Most terminal complement deficiencies are autosomal recessive; first-degree relatives should be tested. 5. **Ongoing prophylaxis:** Some guidelines recommend prophylactic penicillin V or annual meningococcal booster vaccination in confirmed complement-deficient patients. **Clinical Pearl (Harrison's):** Terminal complement (MAC) deficiency is the single most important risk factor for recurrent invasive meningococcal disease. Any patient with ≥2 episodes of meningococcal infection should be evaluated for C5–C9 deficiency after the acute episode resolves.