Skin and Soft-Tissue Infections

SOURCE

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. https://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146071658. Accessed February 23, 2019.

CONDITION/DISORDER SYNONYMS

• Skin and soft-tissue infections (SSTIs)

ETIOLOGY

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

• 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%)

PATHOPHYSIOLOGY

• 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.

EPIDEMIOLOGY

• 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