Streptococcus pneumoniae

1. "Need to cover Streptococcus pneumoniae in ALL cases of CAP" — explicitly stated in GC 052 lecture slide ^[1]. This is the single most examined pneumonia-prescribing principle at HKUMed.
2. "Need to cover Legionella pneumophila in SEVERE cases of CAP" — paired with above in GC 052 ^[1]; a classic MCQ distractor pairing.
3. OPSI (Overwhelming Post-Splenectomy Infection): >50% caused by S. pneumoniae — surfaces in surgery notes and splenomegaly lectures ^[5][6]. Expect MCQ/SAQ on pre-splenectomy vaccination (Pneumococcus, Hib, Meningococcus, Influenza).
4. Complement deficiency (C3, C5–C9) → susceptibility to encapsulated organisms (Pneumococcus, N. meningitidis, H. influenzae) — highlighted in Jerry's immunodeficiencies notes and GC 096 ^[14].
5. IV dexamethasone adjunct for S. pneumoniae meningitis (and S. suis) — give before or with first Abx dose; reduces mortality and hearing loss. No benefit proven for other bacterial meningitis organisms ^[9].
6. Urine pneumococcal antigen test — rapid, unaffected by prior antibiotics, high specificity; a favoured diagnostic investigation in MCQ stems ^[3][4].

• Optochin test: The single best discriminator between S. pneumoniae (sensitive) and viridans group streptococci (resistant). Bile solubility confirms.
• α-haemolysis confusion: Both pneumococcus and viridans strep are α-haemolytic. MCQ distractors may list S. pyogenes (β-haemolytic) or Enterococcus (γ-haemolytic / variable) — know your haemolysis patterns.
• Post-influenza secondary bacterial pneumonia: S. pneumoniae and S. aureus are the two classic causes. If the stem mentions a previously well patient recovering from influenza who deteriorates → think pneumococcus first (most common CAP organism), but S. aureus if necrotising features or MRSA risk factors.
• Serotype 3 escape: A fully PCV13-vaccinated child developing pneumonia with empyema → serotype 3 S. pneumoniae is the classic answer (lower vaccine effectiveness for this serotype) ^[15].
• Meningitis empirical Abx: 3G cephalosporin + vancomycin. Do NOT forget to add ampicillin if risk of Listeria (elderly, immunocompromised, pregnancy) ^[9].
• Rusty sputum = classic for pneumococcal lobar pneumonia. Do not confuse with "currant jelly sputum" (Klebsiella).

1. 2025 Fourth Summative MCQ Q13 ^[15]

"A 36-month-old boy received all vaccines as scheduled in the Hong Kong Childhood Immunisation Programme but was admitted with pneumonia associated with pleural effusion and empyema. Which of the following pathogens is MOST LIKELY the causative agent of his pneumonia?"

Options: A. Influenza virus · B. Measles virus · C. Staphylococcus aureus · D. Streptococcus pneumoniae serotype 3

Answer: D. Serotype 3 is included in PCV13 but vaccine effectiveness against this serotype is notably lower, making it the commonest cause of vaccine-breakthrough invasive pneumococcal disease with empyema in fully vaccinated children. S. aureus can cause empyema but is less likely in a vaccinated child presenting with typical community-acquired pneumonia + empyema.

2. 2024 Fourth Summative MCQ EMQ Section B, Q4 ^[16]

"A 70-year-old man presented with shortness of breath. Abnormal findings were detected during respiratory examination. Select the MOST LIKELY diagnosis: Bronchial breath sound and increased vocal resonance."

Options included: H. Pneumococcal pneumonia (among others)

Answer: H. Pneumococcal pneumonia. Bronchial breath sounds + increased vocal resonance = consolidation, classic for lobar pneumococcal pneumonia.

3. 2022 Fourth Summative MCQ EMQ Section V, Q20 ^[17]

"A 45-year-old man with acute myeloid leukaemia was admitted for the third cycle of chemotherapy. He developed severe and prolonged neutropenia afterwards. While on meropenem, he developed breakthrough fever and worsening oral mucositis. The blood culture was positive."

Options included: G. Streptococcus mitis · H. Streptococcus pneumoniae

Answer: G. Streptococcus mitis (viridans group). This is a trap — breakthrough fever on broad-spectrum Abx with oral mucositis in neutropenic patient points to viridans strep (S. mitis), NOT pneumococcus. Pneumococcus (option H) is a distractor. This is a key discriminator: mucositis + neutropenia + breakthrough on meropenem = viridans strep.

4. 2021 Fourth Summative SAQ Q12c ^[18]

"He did not come back for routine vaccination after transplantation for 1 year. Four years after the transplant, he had a sudden onset of high fever, hypotension, purpuric skin rash and died within 24 hours after hospitalisation. His peripheral blood smear showed Howell-Jolly bodies. List THREE organisms found in blood cultures which may account for this clinical picture."

Answer: S. pneumoniae, N. meningitidis, H. influenzae. Howell-Jolly bodies indicate functional asplenia. This is the classic OPSI triad of encapsulated organisms. S. pneumoniae accounts for >50% of OPSI cases.

5. 2023 Fourth Summative MCQ Q83 ^[19]

"A neonate (day 2 of life) develops high fever, lethargy and feeding difficulty. Sepsis workup is performed including lumbar puncture. [Gram stain image of CSF]. Which of the following microorganisms is MOST LIKELY to be grown in culture from the cerebrospinal fluid?"

Options: A. Enterococcus faecalis · B. Group B streptococcus · C. Staphylococcus aureus · D. Streptococcus pneumoniae

Answer: B. Group B streptococcus. Day 2 neonate = early-onset neonatal sepsis/meningitis → GBS (S. agalactiae) is the classic cause. S. pneumoniae (option D) is a distractor — it causes meningitis in older infants, children, and adults, NOT typically neonates at day 2. This is a key age-based discriminator.