A 3,200-g infant was born at 37 weeks of gestation via repeat cesarean delivery to a woman (gravida 5, para 5) presenting with spontaneous rupture of membranes. The infant appeared healthy with Apgar scores of 8 and 9 at one and five minutes, respectively. No significant maternal history, prodromal symptoms, or abnormal examination findings were noted on admission. Regular prenatal care and testing were unremarkable. The parents denied a history of herpes simplex, but serology testing had not been performed. During establishment of breastfeeding in the first 24 hours of life, several small (1 to 3 mm) lesions were discovered on the mucosal surface of the newborn's lower lip.

Eversion of the infant's lower lip revealed nonfriable, white papules with minimal erythema at the base, intermixed with lesions of more vesicular appearance. No significant pain or discomfort was elicited on palpation. Mucoid, white material could be expressed when scraping pressure was applied to an isolated lesion. The newborn's physical examination was otherwise unremarkable, and his vital signs were within normal limits.

Question

Based on the patient's history and physical examination findings, which one of the following is the most likely diagnosis?