Bacterial Infections of Skin and Skin Structures

A 12-year-old female was evaluated in the emergency department (ED) for a swelling on her right leg. She is previously healthy; however, she has several mosquito bites on her leg which she has been scratching. Over the past 12 hours, she has had worsening redness and swelling around one of the mosquito bites, with associated fevers and vomiting. In the ED, she is febrile to 39 °C. Her physical examination is significant for a 10-cm tender area of redness, induration, warmth, and fluctuance on her right leg just above her knee. Incision and drainage of the abscess are performed at the bedside. The evacuated purulent material is sent for Gram stain and bacterial culture. She is admitted to the hospital and treated with intravenous vancomycin and cefazolin to target the most likely causes of the infection: Streptococcus pyogenes and methicillin-susceptible and methicillin-resistant Staphylococcus aureus. Culture results reveal Staphylococcus aureus, a catalase-positive, coagulase-positive gram-positive coccus typically seen as purple grape-like clusters on Gram stain. Rapid latex agglutination testing is positive for the detection of penicillin-binding protein (PBP) 2A. Expression of this protein further identifies the organism as methicillin-resistant S. aureus (MRSA). IV cefazolin was discontinued. Vancomycin is continued while awaiting the full antimicrobial susceptibility report. On hospital day 2, antimicrobial susceptibilities reveal that the isolate is susceptible to clindamycin. At this time, the patient is afebrile, showing signs of clinical improvement, and tolerating oral intake without vomiting. Her treatment is switched from IV vancomycin to oral clindamycin, and she is discharged home with a diagnosis of MRSA skin abscess. Her infection resolves completely after treatment with a 10-day course of clindamycin.