Abscess

An abscess is a localized collection of pus within tissue, most commonly caused by the bacterium Staphylococcus aureus. It represents a defensive reaction of the host immune system attempting to confine infection and prevent systemic spread.

Pus inside an abscess consists of:

• Neutrophils (dead and dying)

• Liquefied necrotic tissue

• Bacteria

• Inflammatory mediators

• Protein-rich exudate

A defining feature of an abscess is the formation of a fibrous capsule (pyogenic membrane) that walls off infection from surrounding tissue.Because of this encapsulation, antibiotic penetration is poor — therefore drainage is the cornerstone of treatment.

Abscesses may occur in:

Etiology & Microbiology

Most common organism

• Staphylococcus aureus (including MRSA strains)

Other possible organisms

Pathophysiology

1. Bacterial entry

   • Through micro-trauma (shaving, scratching, injection, insect bite)

2. Innate immune activation

   • Neutrophils migrate to site via chemotaxis

3. Liquefactive necrosis

   • Enzymes digest tissue → pus formation

4. Walling off

   • Fibroblasts form capsule → abscess cavity

5. Pressure buildup

   • Leads to severe throbbing pain

6. Spontaneous rupture or sinus formation

   • If untreated

Risk Factors

Local factors

• Friction areas (axilla, groin, buttocks)

• Hair follicles (folliculitis progression)

• Poor hygiene

• Occlusive clothing

• Shaving

Systemic factors

• Diabetes mellitus

• HIV infection

• Chronic steroid use

• Malnutrition

• Obesity

• Peripheral vascular disease

Behavioral

• Injection drug use

• Sharing razors or towels

Classification

Clinical Features

Local Signs

• Painful tender nodule

• Erythematous inflammatory plaque

• Warmth

• Induration

• Central pustule (“pointing”)

• Fluctuation (fluid movement on palpation)

• Skin thinning and shining

Advanced Local Features

• Spontaneous rupture

• Purulent discharge (yellow/green foul smelling)

• Surrounding cellulitis

• Lymphangitis (red streaks)

• Regional lymphadenopathy

Systemic Symptoms (suggest complicated infection)

• Fever

• Chills

• Malaise

• Tachycardia

• Sepsis (rare but serious)

Diagnostic Criteria

Clinical diagnosis is usually sufficient.

Major criteria

• Painful pus-filled swelling

• Fluctuant palpable mass

• Erythematous plaque

Supportive findings

• Satellite lymph nodes

• Rare fever

• Surrounding cellulitis

The presence of fluctuation strongly indicates a drainable abscess.

Differential Diagnosis

Investigations

Usually not required for uncomplicated abscess

Indications for investigation

• Recurrent abscesses

• Large abscess

• Systemic illness

• Immunocompromised patient

• Treatment failure

Laboratory tests

Imaging

• Ultrasound: differentiate cellulitis vs abscess

• CT/MRI: deep abscess

Treatment

A. Non-Pharmacological

• Warm compresses 15–20 min, 3–4× daily

• Promotes localization and drainage

B. Definitive Treatment — Incision & Drainage (I&D)

Gold standard therapy

Indications

• Fluctuation present

• Size >1–2 cm

• Failure of conservative therapy

Procedure Steps

1. Local anesthesia

2. Incision at most dependent point

3. Evacuate pus completely

4. Break loculations

5. Irrigate with saline

6. Packing if large cavity

Pain relief occurs almost immediately after drainage.

C. Pharmacological Therapy (Adjunctive)

Antibiotics indicated if:

• Surrounding cellulitis

• Fever

• Immunocompromised

• Multiple lesions

• Facial abscess

• Large abscess

Options

Erythromycin

• Adults: 500 mg PO every 8 hours × 7–10 days

• Children: 25–50 mg/kg/day divided 8 hourly

Flucloxacillin

• Adults: 500 mg PO every 6 hours × 7–10 days

• Children: 25 mg/kg every 6 hours

Complications

• Cellulitis

• Septicemia

• Sinus tract formation

• Chronic recurrent abscess

• Scarring

• Osteomyelitis (near bone)

• Cavernous sinus thrombosis (danger area of face)

• Necrotizing infection (rare but life-threatening)

Prevention

• Regular skin hygiene

• Avoid squeezing lesions

• Early treatment of folliculitis

• Control diabetes

• Avoid sharing razors/towels

• Antiseptic wound care

• Decolonization (recurrent cases):

  • Nasal mupirocin

  • Chlorhexidine wash

Patient Education

Seek medical care immediately if:

• Abscess on face or spine

• Fever develops

• Rapid enlargement

• Severe pain

• Recurrent lesions

• Occurs in infant or diabetic patient

Never attempt self-drainage with needles.

Prognosis