Complement Deficiency Meningitis — SCE Infectious Diseases MCQ

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ModerateCNS InfectionComplement Deficiency MeningitisSCE Infectious Diseases

A 50-year-old man develops acute bacterial meningitis. LP shows Gram-negative diplococci. He has a known complement C5 deficiency (terminal complement pathway). What organism is he at highest risk for?

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Correct answer: E — Neisseria meningitidis — terminal complement deficiency (C5–C9) specifically predisposes to recurrent Neisseria infections

Terminal complement deficiency (C5, C6, C7, C8, C9 — the membrane attack complex) specifically predisposes to recurrent Neisseria infections (meningitidis and gonorrhoeae). This is because complement-mediated bacteriolysis is the primary immune mechanism for killing Neisseria. Patients with terminal complement deficiency should receive meningococcal vaccination (MenACWY and MenB) and may require long-term antibiotic prophylaxis. All patients with recurrent meningococcal disease should be screened for complement deficiency.

Reference: UKHSA 2024 – Green Book Ch 22: Meningococcal; NICE 2024 – Complement deficiency; BSACI 2024