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Acute Bacterial Skin And Skin Structure InfectionEdit

Acute Bacterial Skin and Skin Structure Infections (ABSSSI) represent a common group of conditions in which bacteria invade the skin and its underlying structures, producing rapid local signs of infection and, in many cases, systemic symptoms. These infections span a spectrum from nonpurulent inflammation of the skin to purulent processes involving deeper tissues or closed spaces. Clinically, ABSSSI often require timely assessment and selective use of antibiotics, with attention to drainage of abscesses and source control where appropriate. The principal pathogens are skin commensals, most notably Staphylococcus aureus and Streptococcus pyogenes, though the microbiology can be more complex in wounds, bites, diabetic foot infections, or in people with impaired immunity or vascular disease. The category is widely used in research and clinical practice to unify how clinicians describe and treat these infections, and to standardize outcomes in trials of new antibiotics.

The management of ABSSSI sits at the intersection of clinical judgment, microbiology, and health policy. While effective antibiotic therapy is essential in many cases, prudent use—often summarized under antibiotic stewardship—aims to minimize unnecessary exposure, reduce resistance, and control costs, all without compromising patient outcomes. These considerations shape guidelines and practice in outpatient and inpatient settings, influence prescribing patterns, and intersect with debates about access to care, pricing, and innovation in antimicrobial development. The following sections summarize the clinical features, microbiology, diagnostic approach, treatment strategies, and the policy and practice debates surrounding ABSSSI.

Definition and classification

ABSSSI is a clinically defined category that includes infections of the skin and underlying structures with at least some systemic or localized inflammatory signs. The spectrum includes:

  • nonpurulent cellulitis and erysipelas, characterized by diffuse, ill-defined borders, swelling, warmth, and pain;
  • major skin and soft tissue infections, such as abscesses with purulent drainage or areas of extensive wound infection;
  • infections that involve deeper structures, such as the subcutaneous tissue or fascia, when they present with acute signs of infection.

Pathogens typically responsible are Staphylococcus aureus and Streptococcus pyogenes, with other organisms more likely in particular contexts (for example, polymicrobial infections in bites or contaminated wounds). The clinical presentation, severity, purulence, and patient risk factors help determine whether outpatient management with oral antibiotics is appropriate or whether admission and intravenous therapy are warranted.

Epidemiology and risk factors

ABSSSI affects people across ages and populations, but certain risk factors increase the likelihood of infection or complicate management. Common risk factors include:

  • breaks in the skin barrier, such as lacerations, ulcers, or post-surgical wounds;
  • diabetes mellitus and peripheral vascular disease, which impair host defenses and healing;
  • immune suppression or chronic illnesses that affect wound healing;
  • obesity, edema, or chronic venous insufficiency that predispose to leg cellulitis;
  • recent antibiotic exposure, which can influence local flora and resistance patterns.

In many settings, MRSA (methicillin-resistant Staphylococcus aureus) contributes to the burden of purulent ABSSSI, while nonpurulent cellulitis remains more often associated with streptococcal species. In wounds or animal/human bites, polymicrobial infection is more common, and anaerobic or Gram-negative organisms may be involved.

Pathogenesis and microbiology

Skin infection begins after bacterial entry through compromised skin or invasive devices. Once bacteria reach the dermis or subcutaneous tissues, they trigger inflammation with neutrophil and cytokine responses. Abscess formation results from localized tissue necrosis and pus accumulation, which often requires drainage for source control. The dominance of certain organisms reflects both colonization patterns and context:

  • Staphylococcus aureus is a leading cause of purulent ABSSSI, including abscesses and furuncles.
  • Streptococcus pyogenes commonly causes nonpurulent cellulitis and erysipelas.
  • Polymicrobial infections can involve enteric Gram-negatives, anaerobes, and other organisms, particularly in wounds, chronic ulcers, or bites.

Antibiotic choices are tailored to the anticipated pathogens, patient factors, and local resistance patterns, with MRSA coverage considered when risk factors or purulence suggest it.

Clinical features and differential diagnosis

ABSSSI typically presents with a combination of local signs—redness, warmth, swelling, tenderness—and may include fever or malaise in more extensive disease. Distinction from noninfectious dermatitis or inflammatory conditions relies on the presence of systemic signs, pus or abscess formation, and imaging when deeper involvement is suspected. Important differentials include:

  • chronic venous stasis changes without acute infection;
  • contact dermatitis or eczematous dermatitis with secondary infection;
  • necrotizing soft tissue infections, which require urgent recognition and aggressive management.

Imaging and laboratory studies are reserved for selected cases. Point-of-care ultrasound can help identify abscesses requiring drainage, while labs such as complete blood count and inflammatory markers (e.g., C-reactive protein) support assessment in more severe presentations.

Diagnosis

Diagnosis is primarily clinical, supported by imaging or microbiology when indicated. Key elements include:

  • assessment of signs of systemic illness (fever, tachycardia) and severity indicators to decide on outpatient versus inpatient management;
  • evaluation for abscesses or necrotizing infection that would demand immediate intervention;
  • microbiological testing (culture) when feasible, particularly in purulent infections or in immunocompromised patients, to guide antibiotic choices;
  • consideration of local resistance patterns to optimize empiric therapy.

Management and therapy

Management of ABSSSI combines local wound care, source control, and antimicrobial therapy tailored to severity and suspected pathogens. Core principles include:

  • incision and drainage for abscesses or purulent collections to achieve source control;
  • appropriate antibiotic therapy based on the clinical scenario, with choices guided by severity, purulence, comorbidities, and local resistance;
    • nonpurulent cellulitis without systemic signs may be treated with narrow-spectrum agents targeting streptococci (for example, first-generation cephalosporins) in appropriate patients.
    • purulent ABSSSI or suspected MRSA coverage often requires agents with anti-staphylococcal activity (e.g., doxycycline, clindamycin, TMP-SMX, or others) depending on local resistance data and patient tolerance.
    • more severe infections or immunocompromised patients may require intravenous therapy with agents effective against MRSA and streptococci (for example, vancomycin or newer MRSA-active beta-lactams) and possibly Gram-negative coverage when indicated by anatomic involvement or risk factors.
  • duration of therapy is generally limited to the shortest effective course (often 5–10 days for uncomplicated ABSSSI, longer if there is slow response or deep involvement), with treatment length individualized to clinical progress.
  • wound care, analgesia, and management of underlying conditions (diabetes control, venous insufficiency) to support healing and prevent recurrence.

Antibiotic choices and durations are increasingly shaped by stewardship principles that emphasize minimizing unnecessary broad-spectrum use, avoiding overtreatment of mild cases, and ensuring rapid drainage when feasible. Guidelines from major professional bodies synthesize evidence to balance efficacy with the risk of resistance development.

Antibiotic stewardship and policy considerations

A central point of debate in ABSSSI management concerns antibiotic stewardship: how to provide effective treatment while limiting the emergence of resistance and controlling costs. Key policy and practice considerations include:

  • ensuring access to timely care and appropriate antibiotics for patients who truly need systemic therapy, while avoiding unnecessary prescriptions for milder cases;
  • selecting empiric therapy that covers likely pathogens given the presentation and setting, with de-escalation to narrow-spectrum agents as culture results permit;
  • balancing cost concerns with the need to support drug development and availability of life-saving antibiotics;
  • addressing disparities in access to care that can influence delayed treatment, complications, and hospitalizations.

From a broader perspective, there are divergent views about how to structure incentives, regulation, and public or private sector roles in antibiotic development and stewardship. Proponents of more market-based approaches emphasize innovation and patient choice, while proponents of tighter stewardship highlight social costs of resistance and the long-term benefits of prudent prescribing. In clinical practice, these policy tensions intersect with day-to-day decisions about which antibiotic to use, how long to treat, and when to pursue hospital-level care.

See also