A 3-month-old unimmunized infant presents with paroxysmal cough lasting 2 weeks, followed by a high-pitched inspiratory whoop and post-tussive vomiting. WBC count is 45,000/mm3 with 70% lymphocytes. Chest X-ray is normal. Which organism is responsible?
- A Bordetella pertussis ✓
- B Mycoplasma pneumoniae
- C Respiratory syncytial virus
- D Haemophilus influenzae type b
Correct answer: A. Bordetella pertussis
Explanation
Pertussis (whooping cough) presents with a catarrhal phase followed by paroxysmal cough with an inspiratory whoop and post-tussive vomiting. Absolute lymphocytosis (>20,000/mm3 with >50% lymphocytes) in an unimmunized infant is characteristic. Bordetella pertussis is the causative organism. RSV causes bronchiolitis; Mycoplasma causes atypical pneumonia; Hib causes epiglottitis or pneumonia.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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