A healthy 38-year-old man presented to a walk-in clinic for evaluation of a rash on his upper neck that his primary care physician had diagnosed as a possible skin abscess 2 days prior. The patient was concerned that the area was not improving despite his taking cephalexin and using topical mupirocin. His symptoms had begun 4 days earlier after he had shaved the ingrown hairs in the area with an older razor while on a business trip. He did not recall any other stress, illness, or other trauma to the area. How would you diagnose this rash?