Summary

Acute soft tissue infection is infection of the skin and underlying tissues (muscle, fascia), which can range from mild cellulitis (superficial skin infection) to life-threatening necrotizing fasciitis (flesh-eating disease). Think of soft tissue infection as bacteria invading your skin and tissues—the infection can spread rapidly, causing inflammation, tissue damage, and potentially death if not treated promptly. The most common type is cellulitis (superficial infection), but more serious types include abscesses (collections of pus), necrotizing fasciitis (infection of the fascia, very serious), and gas gangrene (infection with gas-producing bacteria). The key to management is recognizing the type and severity (cellulitis vs necrotizing fasciitis—the latter is life-threatening), providing appropriate antibiotics (broad-spectrum initially, then targeted), draining abscesses if present, and urgent surgical debridement if necrotizing fasciitis (remove dead tissue). Most cellulitis cases respond well to antibiotics, but necrotizing fasciitis requires urgent surgery and has high mortality if not treated promptly.

Key Facts

• Definition: Infection of skin and underlying soft tissues
• Incidence: Very common (millions of cases/year)
• Mortality: Low for cellulitis (<1%), high for necrotizing fasciitis (20-30%)
• Peak age: All ages
• Critical feature: Redness, swelling, pain, may have systemic symptoms
• Key investigation: Clinical diagnosis (usually), blood cultures, imaging if necrotizing suspected
• First-line treatment: Antibiotics (cellulitis), surgery (necrotizing fasciitis)

Clinical Pearls

"Distinguish cellulitis from necrotizing fasciitis" — Necrotizing fasciitis is life-threatening and needs urgent surgery. Red flags: severe pain out of proportion, rapid progression, crepitus (gas), systemic symptoms. Don't miss this.

"Pain out of proportion is a red flag" — If pain is severe and out of proportion to the appearance, think necrotizing fasciitis. This is a surgical emergency.

"Rapid progression is a red flag" — If the infection is spreading rapidly (hours), think necrotizing fasciitis. Don't wait—this needs urgent surgery.

"Don't delay surgery for necrotizing fasciitis" — Necrotizing fasciitis has high mortality (20-30%). Urgent surgical debridement is essential. Don't wait for imaging if clinical suspicion is high.

Why This Matters Clinically

Soft tissue infections are very common, and most (cellulitis) respond well to antibiotics. However, necrotizing fasciitis is life-threatening and requires urgent recognition and surgery. Early recognition (especially distinguishing cellulitis from necrotizing fasciitis), appropriate antibiotics, and urgent surgery if necrotizing fasciitis are essential. This is a condition that all clinicians need to recognize, as delayed treatment of necrotizing fasciitis can be fatal.

Structured Approach: ABCDE

A - Airway

• Assessment: Usually patent
• Action: Secure if compromised

B - Breathing

• Look: Usually normal (may have difficulty if sepsis)
• Listen: Usually normal
• Measure: SpO2 (usually normal)
• Action: Support if needed

C - Circulation

• Look: May have signs of sepsis
• Feel: Pulse (may be high), BP (may be low)
• Listen: Heart sounds (usually normal)
• Measure: BP (may be low), HR (may be high)
• Action: Monitor if sepsis

D - Disability

• Assessment: Usually normal (may be altered if sepsis)
• Action: Assess if severe

E - Exposure

• Look: Full examination, assess infection
• Feel: Temperature, crepitus, tenderness
• Action: Complete examination

Specific Examination Findings

Local Examination:

• Inspection: Redness, swelling, blisters, necrosis
• Palpation:
  • Temperature: Warm
  • Tenderness: Painful
  • Crepitus: Gas under skin (if necrotizing)
  • Fluctuance: Abscess (if present)
• Extent: Measure extent, track progression

Signs of Necrotizing Fasciitis:

• Severe pain: Out of proportion
• Rapid progression: Spreading rapidly
• Crepitus: Gas under skin
• Blisters: Skin blisters
• Necrosis: Dead tissue
• Systemic: Fever, unwell

Special Tests

Natural History (Without Treatment)

Untreated Soft Tissue Infection:

• Cellulitis: May spread, become more serious
• Necrotizing fasciitis: High mortality (30-50%)
• Poor outcomes: If not treated

Outcomes with Treatment

Factors Affecting Outcomes:

Good Prognosis:

• Early treatment: Better outcomes
• Cellulitis: Usually recovers completely
• No complications: Better outcomes
• Young, healthy: Better outcomes

Poor Prognosis:

• Delayed treatment: Higher mortality (necrotizing)
• Necrotizing fasciitis: Higher mortality
• Extensive disease: Higher amputation risk
• Older, comorbidities: May have worse outcomes

Prognostic Factors

Key Guidelines

1. IDSA Guidelines (2014) — Practice guidelines for the diagnosis and management of skin and soft tissue infections. Infectious Diseases Society of America

Key Recommendations:

• Antibiotics for cellulitis
• Urgent surgery for necrotizing fasciitis
• Evidence Level: 1A

2. NICE Guidelines (2015) — Cellulitis and erysipelas: antimicrobial prescribing. National Institute for Health and Care Excellence

Key Recommendations:

• Similar to IDSA
• Evidence Level: 1A

Landmark Trials

Multiple studies on antibiotic treatment, surgical outcomes.

Evidence Strength

What is a Soft Tissue Infection?

A soft tissue infection is an infection of your skin and the tissues underneath. Think of it as bacteria getting into your skin and tissues, causing redness, swelling, and pain. Most soft tissue infections (cellulitis) are mild and respond well to antibiotics, but some (necrotizing fasciitis) are very serious and need urgent surgery.

In simple terms: Your skin and tissues have become infected. Most cases are mild and get better with antibiotics, but some are serious and need urgent treatment.

Why does it matter?

Most soft tissue infections (cellulitis) are mild and respond well to antibiotics. However, some (necrotizing fasciitis) are life-threatening and need urgent surgery. Early recognition and appropriate treatment are essential. The good news? Most cases respond well to treatment.

Think of it like this: It's like your skin getting infected—most cases are easily treated, but some need urgent care.

How is it treated?

1. Assessment:

• Examination: Your doctor will examine the infection to see how serious it is
• Tests: You may have blood tests
• Why: To see if it's a mild infection (cellulitis) or serious (necrotizing fasciitis)

2. Treatment:

• If mild (cellulitis): You'll get antibiotics (usually by mouth, or through a drip if more severe)
• If serious (necrotizing fasciitis): You'll need urgent surgery to remove dead tissue, plus antibiotics
• If abscess: The pus will be drained (surgically or with a needle)

3. Supportive Care:

• Rest: Rest the affected area
• Elevation: Elevate if on a limb
• Pain relief: Medicine for pain

The goal: Fight the infection (antibiotics, surgery if needed) and help you recover.

What to expect

Recovery:

• Mild cases (cellulitis): Usually start improving within days with antibiotics
• Severe cases: May take longer, may need surgery
• Full recovery: Most people recover completely

After Treatment:

• Antibiotics: You'll continue antibiotics until the infection is cleared
• Monitoring: Your doctor will monitor to make sure you're improving
• Surgery: If you had surgery, you'll recover from that

Recovery Time:

• Mild cases: Usually days to weeks
• Severe cases: May take weeks to months
• If necrotizing: Usually takes longer, may need multiple operations

When to seek help

Call 999 (or your emergency number) immediately if:

• You have a skin infection with severe pain that's out of proportion
• Your skin infection is spreading rapidly (hours)
• You have a skin infection and feel very unwell or have a high fever
• You have a skin infection and can feel gas under your skin (crepitus)
• You have a skin infection and have blisters or dead-looking skin

See your doctor if:

• You have redness, swelling, and pain in an area of skin
• You have a skin infection that's not getting better
• You have concerns about a skin infection

Remember: If you have a skin infection with severe pain, rapid spreading, or you feel very unwell, especially if you can feel gas under your skin or have blisters, call 999 immediately. Most skin infections are easily treated, but some (necrotizing fasciitis) are life-threatening and need urgent surgery. Don't delay—if you're worried, seek help immediately.