Skip to Main Content


Source: Fagan S, Hess D. Skin and soft-tissue infections. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. Accessed February 23, 2019.


  • Skin and soft-tissue infections (SSTIs)


  • Majority of SSTIs are caused by gram-positive organisms present on the skin (Table 1).

TABLE 110-1Predominant Microorganisms of Normal Skin

  • Staphylococcus aureus and Streptococcus pyogenes account for the majority of community-acquired SSTIs.

  • S. aureus is the most common cause of SSTIs in hospitalized patients (30–40% of these being MRSA).

  • Other nosocomial pathogens include:

    • Pseudomonas aeruginosa (11%)

    • Enterococci (9%)

    • Escherichia coli (7%)


  • Skin serves as a barrier between humans and their environment, functioning as a primary defense mechanism against infections.

  • Conditions that may predispose a patient to the development of SSTIs include:

    • High concentrations of bacteria (>105 organisms)

    • Excessive moisture of the skin

    • Inadequate blood supply

    • Availability of bacterial nutrients

    • Damage to the corneal layer allowing for bacterial penetration

  • Majority of SSTIs result from disruption of normal host defenses such as

    • Skin puncture

    • Abrasions

    • Underlying diseases (eg, diabetes)

  • The nature and severity of the infection depend on the type of microorganism and inoculation.


  • Bacterial infections can be primary or secondary.

    • Primary infections: Areas of previously healthy skin and are caused by single pathogen.

    • Secondary infections: Areas of previously damaged skin and are frequently polymicrobic.

  • SSTIs can be classified and differentiated into the following categories (Table 2):

    • Complicated SSTIs

      • Involve deeper skin structures

      • Require significant surgical intervention

      • Occur in patients with compromised immune function such as

        • Diabetes mellitus

        • HIV

      • Uncomplicated

      • Necrotizing

      • Non-necrotizing

      • Purulent

      • Nonpurulent

    • Emergency room (ER) visits for SSTIs have dramatically increased primarily due to an increase in community-associated methicillin-resistant S. aureus (CA-MRSA) cellulitis and abscesses.

    • Exact incidence of SSTIs is unknown, but the frequency of infections caused by drug-resistant gram-positive cocci has been increasing.

    • Treatment choices for SSTIs have been further complicated by increased incidence of macrolide-resistant strains of Streptococcus species

TABLE 110-2Bacterial Classification of Important Skin and Soft-Tissue Infections

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.