Infectious Diseases in Critical Care Medicine

viridans, andEnterococcusspp. can also be isolated.Acinetobacterspp. are found in 25% of the
populations axillae, toe webs, groin, and antecubital fossa. Other gram-negative bacilli are found
more rarely on the skin, and these includeProteusandPseudomonasin the toe webs and
EnterobacterandKlebsiellaon the hands. Antibiotics disturb the balance within commensal flora
and leave the surface vulnerable to colonization by exogenous gram-negative bacilli and fungi.
The principal fungal flora is lipophilic yeasts of the genusMalassezia, and nonlipophilic yeasts
such asCandidaspp. are also inhabitants of the skin (1,2,4).
Primary skin infections occur in otherwise normal skin and are usually caused by
group A streptococci orS. aureus. Secondary infections complicate chronic skin conditions
(e.g., eczema or atopic dermatitis). A deficiency in the expression of antimicrobial peptides may
account for the susceptibility of patients with atopic dermatitis to skin infection withS. aureus
(8). These underlying disorders act as a portal of entry for virulent bacteria. Other factors
predisposing to skin infections include vascular insufficiency, disrupted venous or lymphatic
drainage, sensory neuropathies, diabetes mellitus, previous cellulitis, foreign bodies, accidental
or surgical trauma, burns, poor hygiene, obesity, and immunodeficiencies.

CLASSIFICATION OF SKIN AND SOFT TISSUE INFECTIONS
Infections of the skin and soft tissue can be divided on the basis of the depth of penetration and
the ability of the organism to produce necrosis. Infection of the outermost layer of skin, the
epidermis, is termed impetigo. Extension into the superficial dermis with involvement of
lymphatic is typical of erysipelas, whereas cellulitis is an extension into the subcutaneous
tissue. In necrotizing fasciitis (NF), there is involvement of fascia, whereas in myonecrosis
there is involvement of muscle. A clinically useful distinction with important management
implications subdivides soft tissue infections into nonnecrotizing and necrotizing processes
(9). The Center for Drug Evaluation and Research for development of antimicrobial drugs has
classified skin and soft tissue infection as uncomplicated or complicated. The uncomplicated
category included simple abscesses, impetiginous lesions, furuncles, and cellulitis. Compli-
cated category included infection involving the deeper layer or requiring significant surgical
intervention. Superficial infection in an anatomical site with a risk of gram-negative pathogen
or anaerobes such as the rectal area was also considered to be complicated (10). DiNubile and
Lipsky classified skin and soft tissue infections to assist clinician in recognizing uncomplicated
and complicated infections (11).
Classification can also be based according to the severity of local and systemic signs
and symptoms of infection, and the presence and stability of any comorbidities. Class 1
patients have no signs or symptoms of systemic toxicity without any comorbidities and can
be managed in an outpatient setting. Class 2 patients are systemically ill without any
unstable comorbidities. Class 3 patients have toxic appearance, one unstable comorbidity,
or a limb-threatening infection, whereas class 4 patients have sepsis syndrome or serious

Table 1 Classification of Skin and Soft Tissue Infection Based on Uncomplicated and Complicated Infections and
Systemic Syndromes

Uncomplicated Complicated Systemic syndromes

Superficial: impetigo, ecthyma Secondary infection of diseased skin Scalded-skin syndrome
Deeper: erysipelas, cellulitis
Hair follicle associated:
folliculitis, furunculosis

Acute wound infections: Traumatic

Bite related

Post operative

Toxic shock syndrome

Purpura fulminans

Abscess: carbuncle,
cutaneous abscess

Chronic wound infections: Diabetic foot infections

Venous stasis ulcer

Pressure ulcers

Perianal infections

Necrotizing fasciitis (type 1 and type 2)

Myonecrosis (crepitant and noncrepitant)

Source: Adapted in part from Ref. 11.

296 Sharma and Saravolatz