Pertussis — RACP Paediatrics MCQ

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EasyInfectious DiseasePertussisRACP Paediatrics

A 6-year-old child presents with a 3-week history of a worsening cough, initially catarrhal then paroxysmal with post-tussive vomiting and an inspiratory whoop. FBC shows a lymphocyte count of 25 x 10^9/L. What is the causative organism?

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Correct answer: A — Bordetella pertussis

Pertussis has 3 stages: catarrhal (1-2 weeks, most infectious), paroxysmal (2-8 weeks, characteristic whooping cough), and convalescent. Marked lymphocytosis is characteristic. PCR of nasopharyngeal aspirate confirms diagnosis. Macrolide treatment (azithromycin) reduces infectivity but does not shorten illness duration if given after paroxysmal stage onset.

Reference: Therapeutic Guidelines – 2024 – Antibiotic: Pertussis