A 30-year-old man presents to his physician with a rash on his left leg. He reports that the rash started as a bug bite and is spreading. He denies any fever, chills, or malaise. His medical history is significant for type 1 diabetes mellitus, and his only medication is insulin. On examination of the left leg, there is a 4-cm area of erythema, swelling, and warmth with indistinct margins. There is no gross purulence.
What antibiotic should this patient receive?
A. Oral cephalexinOral clindamycin. This is a straightforward case of cellulitis, which is typically caused by Streptococcus pyogenes or Staphylococcus aureus. Patients with risk factors for MRSA (previous MRSA infection or colonization, diabetes, HIV infection, recent hospitalization or antibiotics, IV drug use, etc.) or with gross purulence should receive an antibiotic that has MRSA coverage. Therapy is usually empiric (since skin cultures are rarely helpful) and is based on the clinical diagnosis and patient’s risk factors. (A, B) Cephalexin and dicloxacillin are both appropriate antibiotics if MRSA was not a concern. (D) Although vancomycin has activity against MRSA, this patient has a localized infection without systemic symptoms and therefore can be treated as an outpatient with oral therapy.
For the sake of the shelf examination, there are a few other important soft tissue infections to know. Erysipelas is a more superficial infection of the dermis and is raised with distinct margins. The majority of cases are due to group A strep. Necrotizing fasciitis is caused by virulent strains of group A strep or MRSA and presents with a rapidly expanding lesion that is severely painful and may have crepitation. Treatment is with debridement and antibiotics to cover group A strep and MRSA (e.g., penicillin and clindamycin) unless the history and risk factors suggest an alternative pathogen. Gas gangrene is a life-threatening infection caused by Clostridium perfringens that spreads rapidly with necrosis and significant crepitus; treatment is with debridement and antibiotics (also penicillin and clindamycin). If the patient has a penetrating injury (e.g., diabetic patient that stepped on a nail that penetrated his shoe), consider Pseudomonas. In gardeners, consider Sporothrix schenckii, which spreads via lymphatics and causes ulcerating nodules. If there is exposure to saltwater, consider Vibrio vulnificus.