Pertussis — branching viva

Opening question

Examiner: Take me through this infant. What is the most likely diagnosis, and what is your frame for managing it? ^[8]

Candidate: The most likely diagnosis is pertussis. The combination of apnoea and cyanosis in a ten-week-old, a three-week household cough contact in the mother, and the infant being between doses of the DTaP schedule is classic for infant pertussis — and the whoop is often absent at this age, so apnoea may be the only sign. My frame is two-layered: support and protect this infant now, and run the public-health response to stop transmission to other vulnerable contacts. I would admit for monitoring, confirm with PCR, start a macrolide, isolate, notify and trace contacts. ^{[8] [1]}

Examiner: Why is the infant at particular risk? ^[8]

Candidate: Infants under six months carry the highest morbidity and mortality in pertussis. They are often too young to have completed the primary series, so they depend on maternal antibody and the immunity of the people around them. Their small airways and limited respiratory reserve turn the same toxin-mediated injury that causes a prolonged cough in an older child into apnoea, cyanosis, pneumonia and, through hypoxia, encephalopathy. The biology is the same; the host turns it lethal. ^[8]