Malignant pertussis in a young infant.

Pertussis remains a significant threat to young infants, even in an age of widespread vaccination. In its most severe form, malignant pertussis (MP), the infection can trigger a life-threatening immune reaction, including a high white blood cell count that can place significant stress on a baby's heart and lungs. This clinical challenge is especially relevant in areas such as the Gulf Cooperation Council, where young demographics and rapidly advancing healthcare systems struggle with outbreaks that are often under-reported. In this context, we detail the case of a young infant who developed MP. The child's course was fraught with extreme leucocytosis, respiratory failure and additional bloodstream infections acquired during hospitalisation. Early recognition, aggressive supportive care and vigilant monitoring are crucial; in addition, timely maternal immunisation is the strongest defence for newborns. The successful use of hydroxyurea to manage extreme hyperleucocytosis without the need for exchange transfusion or leucapheresis is a key educational feature of this case.