Rapidly progressive methicillin-susceptible Staphylococcus aureus abscess of the lower lip: A case report.

Acute bacterial infection of the lip is uncommon and may initially resemble traumatic, allergic, inflammatory, viral, or odontogenic disease. A 26-year-old Caucasian man developed a painful furuncle-like lesion on the lower-lip vermilion after an arthropod bite while travelling in Mexico. Within 48 h, the lesion progressed to marked lower-lip oedema, severe pain, ulceration, crusting, purulent drainage, and fever, despite local incision and oral amoxicillin-clavulanate. After urgent reassessment in Italy, repeat drainage was performed and empirical intravenous vancomycin was started. Ultrasonography showed diffuse hypoechoic oedematous thickening without a definite collection, whereas maxillofacial computed tomography demonstrated a 30 × 16 x 17 mm paramedian abscess with hyperaemic walls and a thin tract towards the cutaneous surface. Purulent material grew methicillin-susceptible Staphylococcus aureus resistant to penicillin and tetracycline, while blood cultures remained negative. Clinical improvement was evident within 48 h after repeat drainage and intravenous therapy, allowing de-escalation to oral cephalexin with complete resolution after a 7-day course. This case illustrates how rapidly progressive lip swelling may conceal an organised abscess, particularly when early source control is incomplete. In this anatomical site, persistent progression despite initial treatment should prompt microbiological sampling, cross-sectional imaging when ultrasonography is inconclusive, timely drainage, and culture-guided antimicrobial de-escalation.