A 12-year-old boy presents with a persistent nonproductive cough for 3 weeks, associated with nocturnal paroxysms, inspiratory whoops, intermittent posttussive vomiting, and on and off wheezing. His appetite has been poor, and he has lost a total of 2 kg of weight during this period. He was started on a 5-day course of amoxicillin approximately 10 days ago, but showed no improvement in symptoms. He was completely healthy earlier, with unremarkable medical and surgical histories. All immunizations are up-to-date.