Impetigo Honey-Colored Crust

A 5-year-old boy presents to the paediatric clinic with a 4-day history of a spreading rash around the nose and mouth. The lesions started as small red spots after a recent cold, progressed through tiny vesicles and pustules, and are now covered by thick crusts. On examination, multiple superficial erosions are noted on the chin, philtrum, and nostrils. The structure marked **A** in the diagram shows the characteristic appearance of these lesions. Which of the following best describes the pathognomonic feature of this condition?