**Question:** 3 year old sister of a neonate is suffering from pertussis, which has been documented by isolation and culture of the organism. Most appropriate statement regarding this clinical situation is -

A. The 3-year-old sister acquired the infection from the neonate
B. The 3-year-old sister is a carrier of the pertussis organism
C. The 3-year-old sister developed the infection independently
D. The 3-year-old sister vaccinated against pertussis

**Correct Answer:**

**Core Concept:** Pertussis is a respiratory illness caused by the bacterium Bordetella pertussis, which attacks the respiratory system, particularly the trachea and bronchi. The disease is characterized by a series of symptoms, including whooping cough, paroxysmal coughing fits, and post-tussive vomiting.

**Why the Correct Answer is Right:** In this scenario, the 3-year-old sister is suffering from pertussis, which has been confirmed through isolation and culture of the organism. This indicates that the infection is present and active in her body, suggesting that she has contracted the infection rather than being a carrier or having developed the disease independently.

**Why Each Wrong Option is Incorrect:**

A. The statement that the 3-year-old sister acquired the infection from the neonate is incorrect because isolation and culture confirm the presence of the pertussis organism in her respiratory system, indicating active infection rather than transmission from the neonate.

B. The statement that the 3-year-old sister is a carrier of the pertussis organism is false because the presence of the organism in her respiratory system confirms active infection, not carriage.

C. The statement that the 3-year-old sister developed the infection independently is incorrect, as the isolation and culture confirm the presence of the pertussis organism in her respiratory system, indicating active infection.

D. The statement that the 3-year-old sister vaccinated against pertussis is irrelevant, as pertussis vaccination status is unrelated to the infection status in this scenario.

**Clinical Pearl:** Although pertussis vaccination is highly effective in preventing pertussis, the correct answer focuses on the evidence from isolation and culture of the pertussis organism in the 3-year-old sister's respiratory system, which confirms active infection.

**Explanation:**

The correct answer is Option C ("The 3-year-old sister developed the infection independently.") because the isolation and culture of the pertussis organism in the 3-year-old sister's respiratory system clearly indicates that she has contracted the infection and is experiencing an active case of pertussis. The other options are incorrect because:

1. Option A focuses on transmission from the neonate, which is not supported by the evidence of active infection in the 3-year-old sister.
2. Option B suggests the sister is a carrier, but the evidence from isolation and culture confirms active infection, not carriage.
3. Option D is irrelevant as it discusses vaccination status, which does not address the presence of the pertussis organism in the 3-year-old sister's respiratory