Haemophilus influenzae

1. GC 105 — "Haemophilus influenzae: severe sepsis, meningitis, epiglottitis (Hib) vaccine-preventable; sinusitis, otitis media (non-typeable Hi) no vaccine" ^[1]. This is the core distinction examiners test: Hib = invasive/vaccine-preventable vs NTHi = mucosal/no vaccine.

2. GC 105 — HACEK group includes Haemophilus: "fastidious organisms; rare cause of infective endocarditis" ^[1]. HACEK IE classically presents with large vegetations and may be initially culture-negative — ask lab for prolonged incubation.

3. Bronchiectasis lecture — "H. influenzae is the commonest bacterial isolate in early and milder bronchiectasis; Pseudomonas aeruginosa in long-standing and severe patients" ^[7]. This is a high-yield discriminator for sputum culture interpretation questions.

4. Felix Lai Paeds notes — "Hib infection has a relatively lower occurrence in HK compared with other Western countries and thus is NOT included in Childhood Immunisation Programme" ^[5]. This directly feeds into MCQ traps where a vaccinated-per-CIP child still gets Hib because the vaccine was never given.

5. Jerry's immunodeficiencies — complement deficiency (C3, C5-C9) → susceptibility to encapsulated bacteria including H. influenzae ^[9]. Classic exam setup: young man with recurrent Neisseria/Hi infections → check CH50, AH50, complement levels.

6. Splenectomy vaccination protocol: Pneumococcus, H. influenzae type b, Meningococcus, Influenza — all four must be given >2 weeks pre-op (elective) or ASAP post-op (emergency) ^[8]. The mnemonic from surgery notes: "Some Nasty Killers Have Some Capsule Protection" covers the key encapsulated organisms.

• Hib vaccine in HK CIP trap: A fully vaccinated (per HK schedule) child presenting with invasive H. influenzae disease is possible because Hib is NOT in the government programme. However, if the question asks about a child vaccinated per CIP with pneumonia + empyema, the answer is S. pneumoniae serotype 3 (PCV13 does not cover all serotypes well, especially serotype 3) — not Hib ^[11].
• Epiglottitis vs croup: Epiglottitis = Hib, acute onset, drooling, tripod position, "thumb sign" on lateral neck X-ray, NO barking cough. Croup = parainfluenza, barking cough, "steeple sign" on AP neck X-ray.
• Septic arthritis age discriminator: < 2 years = H. influenzae type b; > 2 years/adults = S. aureus; sexually active = N. gonorrhoeae ^[13].
• Meningitis prophylaxis: Rifampicin for both N. meningitidis and H. influenzae contacts, but doses differ (Hi: 20 mg/kg OD ×4 days; meningococcus: 10 mg/kg BD ×4 days in children) ^[10].
• Post-splenectomy vaccination MCQ: MMR is NOT required post-splenectomy (it protects against viruses, not encapsulated bacteria). The 2024 MCQ Q51 tests exactly this ^[12].

2022 Fourth Summative MCQ Q18 ^[11]:

"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? A. Haemophilus influenzae type B; B. Influenza virus; C. Staphylococcus aureus; D. Streptococcus pneumonia serotype 3"

• Answer: D — Streptococcus pneumoniae serotype 3
• Rationale: The child received all CIP vaccines (including PCV13) but Hib is NOT in HK CIP, so option A might seem tempting. However, the question says "all vaccines as scheduled" — since Hib is not scheduled, this does not exclude Hib. The key discriminator is that pneumonia with empyema in a vaccinated child is classically due to S. pneumoniae serotype 3, which is poorly covered by PCV13 despite being included (poor immunogenicity for serotype 3). S. aureus can cause empyema but is less common than pneumococcus as a community pathogen in this age group.

2024 Fourth Summative MCQ Q51 ^[12]:

"Which of the following vaccinations may NOT be necessary in adults (age > 19 years) after elective splenectomy? A. Haemophilus influenzae type b vaccine; B. Measles, Mumps, or Rubella (MMR) vaccine; C. Meningococcal serotype ACWY and serotype B vaccine; D. Pneumococcal vaccine"

• Answer: B — MMR vaccine
• Rationale: Post-splenectomy vaccination targets encapsulated bacteria (pneumococcus, Hib, meningococcus) + influenza. MMR protects against viral infections and is unrelated to asplenia risk. Hib vaccine (option A) IS necessary post-splenectomy.

2021 Fourth Summative SAQ Q12(c) ^[14]:

"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: Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae (type b)
• Rationale: Howell-Jolly bodies indicate functional asplenia (post-BMT with splenic dysfunction). The fulminant sepsis picture = overwhelming post-splenectomy infection (OPSI) caused by encapsulated organisms. These are the classic three to list.