Paper II — 2024 March (Supplementary) (2019 Scheme) — Q8
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Paper II
2024 March (Supplementary) (2019 Scheme) · 100 marks · 180 min
Question
Laboratory diagnosis of pneumococcal meningitis
Q84 marksShort Answers
Answer
Laboratory diagnosis of pneumococcal meningitis (caused by Streptococcus pneumoniae)
CSF examination — typically shows raised opening pressure, markedly elevated protein, low glucose (CSF:blood glucose ratio <0.4), and a neutrophilic pleocytosis (high white cell count, predominantly neutrophils), consistent with acute bacterial meningitis.
CSF Gram stain — demonstrates Gram-positive diplococci (lancet-shaped, in pairs), a rapid presumptive test with reasonably high sensitivity in untreated bacterial meningitis.
CSF culture — on blood agar/chocolate agar, showing alpha-haemolytic, draughtsman colonies; optochin sensitivity and bile solubility confirm S. pneumoniae and distinguish it from other alpha-haemolytic streptococci (viridans group); remains the gold standard, also allowing antimicrobial susceptibility testing.
Latex agglutination test — rapid detection of pneumococcal capsular antigen directly in CSF, useful particularly when the patient has already received antibiotics (which reduces culture yield).
Blood culture — often positive concurrently, given associated bacteraemia.
PCR — increasingly used for rapid, sensitive molecular confirmation, particularly valuable in partially treated meningitis where culture may be falsely negative.
Quellung reaction — capsular swelling reaction using type-specific antiserum, for serotyping.
