An abscess is a localized inflammatory process in which the white blood cells accumulate at the site of infection in the dermis and/or subcutaneous tissue, creating a collection of pus. Commonly associated pathogens are Staphylococcus aureus, streptococci, and normal skin flora. Trauma or any break in the skin barrier predisposes to abscess formation.

Lesions evolve over days to 1-2 weeks. They are usually painful / tender, erythematous, warm, and fluctuant masses that are sometimes associated with fever. A tender subcutaneous nodule with overlying erythema but minimal fluctuance may be an early presentation. Incision and drainage is the mainstay of therapy. In an otherwise healthy, ambulatory patient, the addition of antibiotics is not indicated. Indications for the addition of antibiotics may include patients who are systemically ill, have a high burden of disease (indicated by concomitant widespread folliculitis or associated cellulitis), are immunosuppressed, or have failed incision and drainage.

Methicillin-resistant S. aureus (MRSA) first emerged as an important nosocomial pathogen in the 1960s. In more recent years, community-acquired outbreaks of MRSA (CA-MRSA) have increasingly been described among healthy individuals lacking the traditional risk factors for such infections (intravenous [IV] drug use, incarceration, participation in contact sports, etc). These strains have a propensity for causing abscesses, furunculosis, and folliculitis and have a unique antibiotic susceptibility profile from health care-associated strains of MRSA (HA-MRSA).

It has been shown that the majority of purulent skin and soft tissue infections presenting to emergency rooms across the United States are caused by CA-MRSA.

Abscesses may have an overlying cellulitis, and this may be mistaken for the primary disease process despite the presence of a purulent fluid collection. It is important to discern whether or not such a pocket of infection is present because treatment without adequate drainage does not afford a cure.