Rationale:

• Because there are so many causes of skin infection, and because other conditions such as allergic reactions may mimic infection, the clinician must gather important clues as to etiology by careful physical exam.
• The physical exam is most useful in distinguishing necrotizing fasciitis from superficial infection.

Evidence:

• A review found that initial exam may fail to detect signs of streptococcal necrotizing fasciitis (34). Subsequent exam may reveal more obvious signs.
• A review reports that if there is an open wound a blunt instrument may be used to probe the wound edges. In streptococcal necrotizing fasciitis the superficial fascia easily dissects away from the underlying tissue planes (35).
• The Infectious Diseases Society guideline notes that woody induration of the subcutaneous tissue may suggest necrotizing fasciitis rather than a more superficial infection early in streptococcal infection (21).

Comments:

• Most nonsuppurative cellulitis is caused by streptococci unless associated with an underlying abscess or penetrating trauma, in which case infection by S. aureus is more likely (21).
• Patients with MRSA infections of the skin may mistakenly report that they have been bitten by a spider. This may be based on the sudden onset of pain at the infection site and/or the appearance of an eschar at the center of an abscess. A study of 91 patients with MRSA abscesses reported eschars in 55%. Of 37 patients with non-MRSA abscesses, only 3 had a central eschar (8%) (36).