Definitions of Skin/Soft Tissue Infections

• Impetigo (see Impetigo): infection of superficial layers of the epidermis
• Cellulitis (see Cellulitis): skin infection of deeper dermis and subcutaneous fat (resulting from bacterial breach of the skin) characterized by erythema, warmth, and edema without an underlying suppurative focus
• Erysipelas (see Erysipelas): skin infection of upper dermis and superficial lymphatics (resulting from bacterial breach of the skin) characterized by erythema, warmth, and edema without an underlying suppurative focus
• Furuncle (Boil) (see Skin Abscess): infection of hair follicle where purulent material extends through the dermis into the subcutaneous tissue, forming a small abscess
• Carbuncle (see Skin Abscess): coalescence of several inflamed follicles into a single inflammatory mass with purulent drainage from multiple follicles
• Skin Abscess (see Skin Abscess): collection of pus within dermis and deeper skin tissues
• Necrotizing Soft Tissue Infection (see Necrotizing Soft Tissue Infection): deep tissue infection involving the hypodermis (and contained structures)
  • All of These are Characterized by Fulminant Tissue Destruction, Systemic Toxicity (Tachycardia >120 Beats/min, Hypotension, Elevated Creatine Kinase, CRP >15 mg/dL, LRINEC Score >6, etc), and High Mortality Rates

Predisposing Factors

• Diabetes Mellitus (see Diabetes Mellitus)
• Immunodeficiency
  • Chronic Granulomatous Disease (CGD) (see Chronic Granulomatous Disease)
• Immunosuppression
• Injection Drug Abuse (see Injection Drug Abuse)
  • Particularly “Skin Popping”
• Nasal Carriage of Staphylococcus Aureus (see Staphylococcus Aureus)
  • May Be the Only Risk Factor Present in a Normal Patient Who Develops Skin Abscess
• Skin Barrier Breach

Microbiology

• General Comments
  • Approximately 7% of Skin Abscess Cases are Polymicrobial (Ann Intern Med, 1977) [MEDLINE] (Br J Surg, 1981) [MEDLINE] (Arch Surg, 1990) [MEDLINE] (Clin Infect Dis, 1995) [MEDLINE]
    • Isolation of Multiple Organisms (Including Staphylococcus Aureus in Combination with Streptococcus Pyogenes and Gram-Negative Bacilli with Anaerobes) is More Common in Patients with Skin Abscess Involving the Following Specific Anatomic Sites
      • Perioral Region
      • Perirectal Region
      • Vulvovaginal Region
• Staphylococcus Aureus (see Staphylococcus Aureus)
  • Staphylococcus Aureus is the Most Common Etiology of Skin Abscess
    • Methicillin-Sensitive Staphylococcus Aureus (MSSA)
    • Methicillin-Resistant Staphylococcus Aureus (MRSA)
• Staphylococcus Epidermidis (see Staphylococcus Epidermidis)
  • Staphylococcus Epidermidis is a Less Common Etiology of Skin Abscess
• Streptococcus Pyogenes (Group A) (see Streptococcus Pyogenes) Streptococcus Pyogenes is a Less Common Etiology of Skin Abscess
• Gram-Negative Bacilli
  • Pseudomonas Aeruginosa (see Pseudomonas Aeruginosa)
    • May Originate from Water Used to Dilute Injection Drugs
  • Other Gram-Negative Bacilli
• Anaerobes
• Nocardiosis (Disseminated) (see Nocardiosis)
  • Subcutaneous Skin Abscesses with/without Sinus Tracts
• Nontuberculous Mycobacteria (see xxxx)
• Blastomycosis (see Blastomycosis)
• Cryptococcosis (see Cryptococcosis)
• Sterile Skin Abscess
  • Most Abscesses are Due to Infection, Sterile Skin Abscesses May Occur in the Setting of Injected Irritants
    • Particularly Oil-Based Irritants May Not Be Fully Absorbed and May Remain at the Site of Injection, Causing Local Irritation
  • Sterile Skin Abscesses Frequently Turn into a Hard, Solid Lesion as it Scars

Diagnosis

Complete Blood Count (CBC) (see Complete Blood Count)

• Findings
  • Leukocytosis (see Leukocytosis)

Blood Culture (see Blood Culture)

• xxxx

Ultrasound

• Useful to Localize a Defined Pocket of Abscess Fluid
  • Studies Indicate that MRSA Can Be Suspected Based on Ultrasound Characteristics of a Skin Abscess (Acad Emerg Med, 2014) [MEDLINE]

Culture of Abscess Drainage Material

• Indicated

Clinical Manifestations

Radiologic Presence of Soft Tissue Gas May Allow Clinical Differentiation of Necrotizing Soft Tissue Infections (NEJM, 2017) [MEDLINE]

Dermatologic Manifestations

Painful/Tender, Erythematous Fluctuant Skin Nodule

• Clinical
  • May Have Central Pustule
  • May Be Surrounded by a Rim of Erythematous Edema

Other Manifestations

Sepsis (see Sepsis)

• XXXXX

Treatment

Small Furuncle

• Warm Compress: when used alone, may promote drainage of the skin abscess

Skin Abscess or Medium-Large Furuncle/Carbuncle

• Incision and Drainage (I+D)
• Indications for Concomitant Antibiotic Therapy (Based on Infectious Disease Society America/IDSA guidelines)
  • Abscess Present in Difficult to Drain Area: face, hand, genitals
  • Associated Septic Phlebitis
  • Comorbid Disease
  • Extreme of Age
  • Immunosuppression
  • Lack of Clinical Response to Incision and Drainage (I+D) Alone
  • Rapid Progression with Associated Cellulitis
  • Severe or Extensive Disease with Multiple Sites of Infection
  • Systemic Toxicity
• Clinical Efficacy
  • Trial of Sulfamethoxazole-Trimethoprim for Skin Abscess (NEJM, 2016) MEDLINE]: in skin abscesses at least 2 cm in size which were drained, sulfamethazole-trimethoprim increased cure rate at 7 and 14 days
    • Wound Cultures were Positive for MRSA in 45% of Cases
    • Abscess Size of At Least 2 cm is Considered a Useful Threshold Regarding Deciding on Antibiotic Use as Adjunctive Therapy for Skin Abscess

References

• Cutaneous abscesses. Anaerobic and aerobic bacteriology and outpatient management. Ann Intern Med. 1977;87(2):145 [MEDLINE] Aerobic and anaerobic bacteriology of subcutaneous abscesses. Br J Surg. 1981;68(7):498 [MEDLINE]
• Aerobic and anaerobic bacteriology of wounds and cutaneous abscesses. Arch Surg. 1990;125(11):1445 [MEDLINE]
• Bacteriology of skin and soft-tissue infections: comparison of infections in intravenous drug users and individuals with no history of intravenous drug use. Clin Infect Dis. 1995;20 Suppl 2:S279 [MEDLINE]
• Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America. Clin Infect Dis. 2014 Jul 15;59(2):e10-52. doi: 10.1093/cid/ciu444 [MEDLINE]
• Management of Skin Abscesses in the Era of Methicillin-Resistant Staphylococcus aureus. N Engl J Med 2014; 370:1039-1047March 13, 2014DOI: 10.1056/NEJMra1212788 [MEDLINE]
• The Massachusetts abscess rule: a clinical decision rule using ultrasound to identify methicillin-resistant Staphylococcus aureus in skin abscesses. Acad Emerg Med. 2014 May;21(5):558-67. doi: 10.1111/acem.12379 [MEDLINE]
• Trimethoprim-Sulfamethoxazole versus Placebo for Uncomplicated Skin Abscess. N Engl J Med. 2016;374(9):823 [MEDLINE]