A child presented with complaints of cough with a characteristic inspiratory whoop. He was not immunised. Sample for investigation is:
**Core Concept**
The child's presentation with a characteristic inspiratory whoop and lack of immunization points towards a specific respiratory infection. This condition is caused by a bacterium that can lead to severe respiratory symptoms in unimmunized children.
**Why the Correct Answer is Right**
The child's symptoms are consistent with pertussis, also known as whooping cough. Pertussis is caused by the bacterium *Bordetella pertussis*, which infects the ciliated epithelial cells of the respiratory tract. The inspiratory whoop is a classic symptom of pertussis, resulting from the intense coughing fits that lead to a characteristic sound. The lack of immunization in the child increases the risk of pertussis infection.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not match the clinical presentation of pertussis. Measles is a different viral infection that presents with a rash, fever, and cough, but not typically with an inspiratory whoop.
**Option B:** This option is incorrect because it does not match the clinical presentation of pertussis. Diphtheria is a bacterial infection caused by *Corynebacterium diphtheriae*, which presents with a severe sore throat, fever, and a membrane covering the tonsils, but not typically with an inspiratory whoop.
**Option C:** This option is incorrect because it does not match the clinical presentation of pertussis. Influenza is a viral infection that presents with a sudden onset of fever, cough, and muscle aches, but not typically with an inspiratory whoop.
**Clinical Pearl / High-Yield Fact**
The characteristic inspiratory whoop of pertussis is often accompanied by a characteristic "coughing fit" that may lead to vomiting, apnea, or even death in severe cases. This highlights the importance of early diagnosis and treatment of pertussis in unimmunized children.
**Correct Answer:** C.