A 6-month-old infant is brought to the emergency department by parents who report the child has been experiencing severe coughing episodes for the past week. Which assessment finding would be most characteristic of pertussis (whooping cough) in this infant?

The classic presentation of pertussis in a 6-month-old involves the paroxysmal stage, which typically begins after 1-2 weeks of nonspecific catarrhal symptoms. The hallmark is a series of rapid, forceful coughs during a single expiration, followed by a sudden, high-pitched inspiratory whoop as air rushes past a narrowed glottis. Post-tussive emesis and exhaustion are common. However, clinicians must recognize that infants under 6 months may not produce the characteristic whoop and instead present with apnea, cyanosis, or gasping, making a high index of suspicion critical.

Key nursing actions include immediate isolation with droplet precautions, continuous cardiopulmonary monitoring for apnea and oxygen desaturation, and gentle supportive care to avoid triggering paroxysms. Suction equipment and emergency airway supplies must be at the bedside. Nasopharyngeal swab for PCR or culture confirms the diagnosis. Macrolide antibiotics (e.g., azithromycin) are initiated early to reduce infectivity, though they do not alter the disease course once the paroxysmal phase has started. All close contacts require post-exposure chemoprophylaxis regardless of immunization status.