Haemophilus influenzae type b vs Nontypeable Haemophilus influenzae
How to tell Haemophilus influenzae type b and Nontypeable Haemophilus influenzae apart when a board question makes them look alike.
Hib: encapsulated and invasive (meningitis, epiglottitis), vaccine-preventable; nontypeable H influenzae: unencapsulated, causes mucosal disease.
Side by side
Encapsulated PRP type b strain causing vaccine-preventable invasive disease such as meningitis, epiglottitis, and pneumonia.
Unencapsulated mucosal strain causing otitis media, sinusitis, COPD exacerbations, and noninvasive respiratory infections.
The PRP capsule blocks phagocytosis and drives invasive Hib disease.
Nontypeable strains colonize respiratory mucosa and cause local mucosal inflammation rather than capsule-driven invasion.
Unimmunized child with meningitis/epiglottitis and PRP capsule clue points Hib.
Vaccinated child with otitis media or adult COPD exacerbation points nontypeable H influenzae.
The trap
The Hib vaccine prevents type b invasive disease, not all nontypeable otitis or COPD exacerbations.
The repair move
For Haemophilus questions, three steps: (1) ask whether the patient is vaccinated (Hib vaccine is part of routine childhood schedule with doses at 2, 4, 6, and 12-15 months); (2) match the clinical syndrome to capsule status meningitis, epiglottitis, septic arthritis, or bacteremia in an unvaccinated child equals Hib (treat with ceftriaxone; rifampin prophylaxis for close contacts under 4 years); mucosal disease (otitis media, sinusitis, COPD exacerbation) equals nontypeable Hib (treat otitis media or sinusitis with amoxicillin first-line, or amoxicillin-clavulanate if beta-lactamase suspected); (3) requires factor X (heme) AND factor V (NAD) for growth on chocolate agar grows around S. aureus colonies (satellite phenomenon).
Try a free question
CoreAn unimmunized child develops meningitis from a small gram-negative coccobacillus with a polyribosyl ribitol phosphate capsule. Which organism type is most likely?
Show answer and explanation
Answer: A. Haemophilus influenzae type b. Hib is encapsulated with PRP capsule and historically caused invasive meningitis, epiglottitis, and pneumonia in children.
Why the other choices are tempting
- B. Nontypeable H influenzae lacks capsule and mainly causes mucosal infections like otitis media, sinusitis, COPD exacerbations, and nonbacteremic pneumonia.
- C. B pertussis causes whooping cough.
- D. Moraxella causes otitis/sinusitis/COPD exacerbations but is not Hib PRP capsule.
- E. N meningitidis is gram-negative diplococcus.
Flashcards
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What is the fastest separator for Haemophilus influenzae type b vs Nontypeable Haemophilus influenzae?
Hib: encapsulated and invasive (meningitis, epiglottitis), vaccine-preventable; nontypeable H influenzae: unencapsulated, causes mucosal disease.
What clue should make you choose Haemophilus influenzae type b?
Encapsulated PRP type b strain causing vaccine-preventable invasive disease such as meningitis, epiglottitis, and pneumonia.
Quick answers
What is the fastest way to tell Haemophilus influenzae type b from Nontypeable Haemophilus influenzae?
Hib: encapsulated and invasive (meningitis, epiglottitis), vaccine-preventable; nontypeable H influenzae: unencapsulated, causes mucosal disease.
What is the key clue for Haemophilus influenzae type b?
Encapsulated PRP type b strain causing vaccine-preventable invasive disease such as meningitis, epiglottitis, and pneumonia.
What is the key clue for Nontypeable Haemophilus influenzae?
Unencapsulated mucosal strain causing otitis media, sinusitis, COPD exacerbations, and noninvasive respiratory infections.
What is the common trap with Haemophilus influenzae type b vs Nontypeable Haemophilus influenzae?
The Hib vaccine prevents type b invasive disease, not all nontypeable otitis or COPD exacerbations.