Skin and soft tissue infections

Red Flags

Pain out of proportion to examination, woody induration, crepitus, skin necrosis, or systemic toxicity — necrotising fasciitis until proven otherwise; emergency surgical consult^[1]
Sepsis criteria with rapidly spreading erythema and bullae — severe non-purulent SSTI; broad-spectrum IV antibiotics within 1 hour, surgical exploration if necrotising^[1]
Diabetic foot infection with loss of protective sensation, deep ulcer, or osteomyelitis features (probe-to-bone) — admit, broad-spectrum cover, surgical consult^[1]
Animal or human bite to hand, face, or over a joint — infection rate >20%; prophylactic amoxicillin-clavulanate, tetanus, rabies risk assessment^[1]

First-line treatment

Interventions

Incision and drainage (I&D)^[1]
Definitive treatment for simple cutaneous abscesses; antibiotics often unnecessary after adequate drainage in immunocompetent patients with single small abscess
Urgent surgical exploration^[1]
Necrotising fasciitis or gas gangrene — immediate aggressive debridement of all necrotic tissue, broad-spectrum antibiotics (e.g. piperacillin-tazobactam + vancomycin + clindamycin for toxin suppression). Mortality climbs steeply with each hour of surgical delay

First-line drug therapy

Drug	Class	Adult	Paediatric	Notes
Cephalexin^[1]	First-generation cephalosporin	500 mg PO QID for 5–7 days	25–50 mg/kg/day divided QID	Mild non-purulent cellulitis (streptococci-dominant). Switch to MRSA cover if no improvement at 48–72 h
Dicloxacillin or flucloxacillin^[1]	Antistaphylococcal penicillin	500 mg PO QID for 5–7 days	25–50 mg/kg/day divided QID	Equivalent first-line for non-MRSA cellulitis where available
Doxycycline or trimethoprim-sulfamethoxazole^[1]	Oral MRSA-active agent	Doxycycline 100 mg PO BD; TMP-SMX 1–2 DS tablets PO BD for 5–7 days	TMP-SMX 8–12 mg/kg/day divided BD (TMP component)	Mild-to-moderate purulent SSTI requiring antibiotics; covers community-acquired MRSA
Vancomycin^[1]	Glycopeptide (IV)	15–20 mg/kg IV q8–12h, target trough 15–20 mg/L	10–15 mg/kg IV q6h	Severe purulent SSTI, suspected/confirmed MRSA, or severe non-purulent cellulitis with systemic toxicity
Piperacillin-tazobactam^[1]	Broad-spectrum antipseudomonal beta-lactam-inhibitor combination	4.5 g IV q8h (extended infusion preferred where available)	300 mg/kg/day divided q6h (max 16 g/day)	Severe SSTI with diabetic foot or polymicrobial concern; combine with vancomycin or linezolid for MRSA cover until cultures return

Cephalexin^[1]

First-generation cephalosporin

Adult: 500 mg PO QID for 5–7 days
Paediatric: 25–50 mg/kg/day divided QID

Mild non-purulent cellulitis (streptococci-dominant). Switch to MRSA cover if no improvement at 48–72 h

Dicloxacillin or flucloxacillin^[1]

Antistaphylococcal penicillin

Adult: 500 mg PO QID for 5–7 days
Paediatric: 25–50 mg/kg/day divided QID

Equivalent first-line for non-MRSA cellulitis where available

Doxycycline or trimethoprim-sulfamethoxazole^[1]

Oral MRSA-active agent

Adult: Doxycycline 100 mg PO BD; TMP-SMX 1–2 DS tablets PO BD for 5–7 days
Paediatric: TMP-SMX 8–12 mg/kg/day divided BD (TMP component)

Mild-to-moderate purulent SSTI requiring antibiotics; covers community-acquired MRSA

Vancomycin^[1]

Glycopeptide (IV)

Adult: 15–20 mg/kg IV q8–12h, target trough 15–20 mg/L
Paediatric: 10–15 mg/kg IV q6h

Severe purulent SSTI, suspected/confirmed MRSA, or severe non-purulent cellulitis with systemic toxicity

Piperacillin-tazobactam^[1]

Broad-spectrum antipseudomonal beta-lactam-inhibitor combination

Adult: 4.5 g IV q8h (extended infusion preferred where available)
Paediatric: 300 mg/kg/day divided q6h (max 16 g/day)

Severe SSTI with diabetic foot or polymicrobial concern; combine with vancomycin or linezolid for MRSA cover until cultures return

Safety-net

Mark the edge of the redness with a pen; if it spreads beyond the line in 24 hours, return same-day^[1]
Severe pain that seems out of proportion to the visible skin redness, blackening, or fluid-filled blisters — call emergency services. This may be a flesh-eating infection^[1]
Fever >38°C, rigors, or feeling unwell with a skin infection — same-day medical review; oral antibiotics may not be enough^[1]

Referral criteria

Suspected necrotising fasciitis (pain out of proportion, crepitus, skin necrosis, rapid progression)Emergency department; immediate surgical exploration^[1]
Sepsis with SSTIEmergency department; IV antibiotics within 1 hour^[1]
Diabetic foot infection with deep involvement, ischemia, or systemic featuresMultidisciplinary diabetic foot service; surgical and vascular review^[1]
Recurrent SSTI (≥3 episodes in 1 year)Infectious diseases for decolonisation strategy and screening for predisposing factors^[1]

Clinical summary

Diagnostic stratification and antimicrobial management of purulent and non-purulent SSTIs by severity, including consideration for necrotising infections.

References

1.2014 IDSA Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections (current; update in progress) (2014)