What is a cutaneous abscess, and how is it diagnosed and managed (including incision and drainage and appropriate antibiotic therapy)?

Cutaneous Abscess: Definition, Diagnosis, and Management

Definition and Clinical Characteristics

A cutaneous abscess is a collection of pus within the dermis and deeper skin tissues, typically presenting as a painful, tender, fluctuant red nodule surrounded by erythematous swelling. 1 These lesions are usually polymicrobial, containing bacteria from normal regional skin flora combined with organisms from adjacent mucous membranes. 1 However, Staphylococcus aureus is the dominant pathogen in bacteria-positive primary skin abscesses. 2

Critical distinction: The term "abscess" should not be confused with "cellulitis"—abscesses involve localized pus collections requiring drainage, while cellulitis refers to diffuse spreading skin infection treated primarily with antibiotics. 3

Diagnosis

Clinical Assessment

• Fluctuance on palpation is the key diagnostic finding, which can be confirmed clinically or by ultrasound if uncertain. 1
• Look for surrounding erythema, warmth, tenderness, and edema. 3
• Assess for systemic signs: fever >38°C, tachycardia >90 bpm, tachypnea >24 breaths/min, or WBC >12,000 or <400 cells/µL (SIRS criteria). 3

Laboratory Testing

• Routine cultures and blood work are NOT recommended for simple, uncomplicated abscesses. 3
• Culture drained fluid only when drainage is performed, to guide antibiotic therapy if needed. 1
• Blood cultures are indicated if bacteremia or sepsis is suspected (fever, hemodynamic instability). 1
• Consider CBC and CRP for complex cases; CRP >100 mg/L suggests severe infection requiring closer monitoring. 1

Management

Primary Treatment: Incision and Drainage

Incision and drainage (I&D) is the definitive treatment for all cutaneous abscesses and must not be delayed. 1 This is more important than antibiotic therapy for simple abscesses. 3

Drainage Technique

• Perform thorough evacuation of pus and probe the cavity to break up loculations. 1
• Use multiple counter-incisions for large abscesses (>5 cm) rather than one long incision to prevent step-off deformity and delayed healing. 1
• Linear incisions are most commonly used (85% of providers). 4

Post-Drainage Wound Management

• Packing is optional and may increase pain without improving outcomes. Small abscesses (<5 cm) heal equally well without packing, and patients report significantly less pain (23.8 mm lower on VAS immediately post-procedure, p=0.014) and use fewer narcotics when not packed. 5
• Irrigation does not improve outcomes. No difference in need for further intervention (15% vs 13%, p=NS) between irrigated and non-irrigated abscesses. 6
• Simple dry dressing is usually sufficient. 1

Antibiotic Therapy: When and What to Use

When Antibiotics Are NOT Needed

For simple abscesses after adequate drainage, antibiotics are unnecessary if the patient has: 1, 7

• Temperature <38.5°C
• WBC <12,000 cells/µL
• Pulse <100 bpm
• Minimal surrounding cellulitis (<5 cm)
• No immunocompromise

When Antibiotics ARE Indicated

Prescribe antibiotics when any of the following are present: 3, 1, 7

• SIRS criteria (temp >38°C or <36°C, HR >90, RR >24, WBC >12,000 or <400)
• Significant surrounding cellulitis (>5 cm of erythema/induration)
• Immunocompromised host (diabetes, chemotherapy, HIV)
• Incomplete source control or multiple abscesses
• Complex locations (perianal, perirectal, axillary, IV drug injection sites)
• Associated conditions (penetrating trauma, MRSA colonization, injection drug use)

Antibiotic Selection

For simple abscesses requiring antibiotics, clindamycin is superior to other options with an 83.1% cure rate and lower recurrence. 1

Recommended regimens: 1

• First-line (trunk/extremities): Clindamycin 300-450 mg PO every 6-8 hours for 7-10 days
• Alternative: TMP-SMX (though clindamycin has better outcomes)
• Penicillin allergy or confirmed MRSA: Clindamycin remains first choice

For complex abscesses (axillary, perianal, perirectal): 1

• Oral: Cephalexin 500 mg every 6 hours PLUS metronidazole 500 mg every 8 hours
• IV (severe): Clindamycin 600-900 mg IV every 8 hours PLUS ciprofloxacin 400 mg IV every 12 hours

Duration: 5-10 days based on clinical response; extend if not improving. 3

Critical caveat: Metronidazole alone has NO role in skin abscess treatment—it lacks activity against S. aureus and streptococci. 1

Special Situations

Recurrent Abscesses

• Search for underlying causes: pilonidal cyst, hidradenitis suppurativa, foreign body. 3
• Culture early and treat with 5-10 days of targeted antibiotics. 3
• Consider decolonization: 5-day regimen of intranasal mupirocin twice daily, daily chlorhexidine washes, and decontamination of personal items. 3, 1

Large or Complex Abscesses

• Abscesses >5 cm may require surgical consultation. 1
• Multiloculated or deep abscesses require aggressive surgical drainage with possible multiple counter-incisions. 1

Follow-Up

• Recommend 48-hour follow-up for wound check and dressing change. 4
• Re-evaluate if no improvement by 5-7 days; consider inadequate drainage, resistant organisms, or underlying condition. 3, 1

Common Pitfalls to Avoid

• Do not treat abscesses with antibiotics alone—drainage is mandatory. 1, 7
• Do not routinely pack small abscesses—it increases pain without benefit. 5
• Do not irrigate routinely—no evidence of benefit. 6
• Do not use metronidazole as monotherapy—ineffective against primary pathogens. 1
• Do not delay drainage while awaiting lab results or attempting antibiotic trial. 1