A previously healthy 18-month-old girl is brought to the office with 2 days of irritability, poor appetite, and pulling at her left ear. She has no known allergies, and her temperature is 102.8 F. She is easily consoled by the mother and moves her neck spontaneously without discomfo. There is a clear discharge from the nares. The left tympanic membrane is erythematous, dull, and bulging. Which of the following virulence factors is generally absent in the strains of the causative organism that produce otitis media, compared with those that produce epiglottitis or meningitis?
A previously healthy 18-month-old girl is brought to the office with 2 days of irritability, poor appetite, and pulling at her left ear. She has no known allergies, and her temperature is 102.8 F. She is easily consoled by the mother and moves her neck spontaneously without discomfo. There is a clear discharge from the nares. The left tympanic membrane is erythematous, dull, and bulging. Which of the following virulence factors is generally absent in the strains of the causative organism that produce otitis media, compared with those that produce epiglottitis or meningitis?
💡 Explanation
**Core Concept**
The question tests the understanding of the virulence factors associated with the causative organism of otitis media, epiglottitis, and meningitis. The correct answer requires knowledge of the pathophysiology and epidemiology of these conditions.
**Why the Correct Answer is Right**
The causative organism of otitis media, Haemophilus influenzae type b (Hib), often lacks the ability to produce the capsule, which is a virulence factor that is typically present in strains that cause epiglottitis or meningitis. The capsule is made of polysaccharide and is important for the organism's ability to invade the bloodstream and cause invasive disease. In otitis media, the Hib strain often colonizes the respiratory tract and causes localized infection without producing invasive disease.
**Why Each Wrong Option is Incorrect**
* **Option A:** The question is specifically asking about the virulence factor that is generally absent in the strains of the causative organism that produce otitis media, not the factor that is associated with otitis media. This option is incorrect because it does not address the question.
* **Option B:** While the capsule is a virulence factor for H. influenzae type b, it is not the correct answer because the question specifically asks about the factor that is absent in the strains that produce otitis media. The capsule is actually more important for invasive disease, such as epiglottitis or meningitis.
* **Option C:** This option is incorrect because it is a virulence factor, not a pathogen that causes disease.
**Clinical Pearl / High-Yield Fact**
The Hib vaccine has been highly effective in reducing the incidence of invasive Hib disease, including epiglottitis and meningitis, in children. However, it does not prevent colonization with Hib, and otitis media caused by Hib remains common in unvaccinated children.
**Correct Answer:** C. Capsule.
✓ Correct Answer: D. Polyribitol phosphate
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