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Cellulitis and other bacterial skin infections

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  • See also

    Periorbital and orbital cellulitis

    Key Points

    1. Cellulitis is a spreading infection of the skin extending to involve the subcutaneous tissues. Many conditions present similarly to cellulitis - always consider differential diagnoses
    2. The typical presenting features of all skin infections include soft tissue redness, warmth and swelling, but other features are variable
    3. Allergic reactions and contact dermatitis are frequently misdiagnosed as cellulitis. If there is itch and no tenderness, cellulitis is unlikely



    • The most common causes are Group A streptococcus (GAS) and Staphylococcus aureus. Predisposing factors include skin abrasions, lacerations, burns, eczematous skin, chickenpox, etc. although the portal of entry of organisms is often not seen

    Impetigo (commonly called "school sores"):

    • Highly contagious infection of the epidermis, particularly common in young children Causative organisms are GAS and S aureus
    • May be associated with scabies

    Staphylococcal scalded skin syndrome (SSSS):

    • Blistering skin disorder induced by the exfoliative (epidermolytic) toxins of S aureus. Primarily affects neonates and young children

    Necrotising fasciitis:

    • Rapidly progressive soft tissue infection characterised by necrosis of subcutaneous tissue
    • Causative organisms include GAS, S aureus, anaerobes and is often polymicrobial
    • It causes severe illness with a high mortality rate (~25%)
    • Recent infection with varicella is a risk factor

    Cellulitis associated with water borne organisms:

    • Aeromonas species (fresh or brackish water, and mud)
    • Mycobacterium marinum (fish tanks)
    • Vibrio species (salt or brackish water)
    • S aureus, including MRSA
    • GAS (coral cuts)

    Infected animal/human bites:

    There are many other forms of skin infection that are not covered in this guideline 


    Typical presentation of all skin infections:

    • Soft tissue redness
    • Warmth and swelling
    • Pain/tenderness

    Mild Cellulitis

    • Features above
    • No systemic features
    • No significant co-morbidities 

    Moderate Cellulitis

    • Features above with moderate swelling and tenderness
    • Systemic features (e.g. fever, tachycardia)

    Severe Cellulitis

    • Features above with severe swelling or tenderness
    • Large body surface area involved (e.g. larger than the patient’s handprint)
    • Marked systemic features (e.g. fever or hypothermia, tachycardia, tachypnoea, altered conscious state, unwell appearance, hypotension – this is a late sign). See sepsis

    Features suggestive of necrotising fasciitis include:

    • Severe pain out of keeping with apparent severity of infection
    • Rapid progression
    • Marked systemic features (e.g. high fever with rigors, tachycardia, tachypnoea, hypotension, confusion, vomiting). See sepsis

    Red flags

    • Abscess or suppuration
    • Animal or human bite
    • Deep structure involvement
    • Foreign body
    • Immunosuppression
    • Lymphangitis
    • MRSA infection
    • Multiple comorbidities
    • Periorbital / facial / hand involvement
    • Varicella associated infection

    Differential Diagnosis

    Large local reactions to insect bites are a common mimic of cellulitis. Features include:

    • A punctum at the site
    • Itch is a prominent feature
    • Redness and induration, but rarely pain



    • Swab for Gram stain (charcoal / gel / bacterial transport swab and slide) and culture if discharge present
    • Blood culture is not useful in mild/moderate cellulitis
    • Consider imaging (e.g. ultrasound) if abscess, deep infection or foreign body suspected


    Manage sepsis if features present
    Manage source if identifiable i.e. remove foreign body, drain abscess
    For ongoing management refer to flowchart below


    Summary of antibiotic therapy

    Antimicrobial recommendations may vary according to local antimicrobial susceptibility patterns; please refer to local guidelines
    Cellulitis frequently looks worse after 24 hours of treatment; consider waiting 48 hours to change therapies
    Young, unvaccinated children are at risk of Haemophilus influenzae type B (Hib)



    Total duration



    Topical Mupirocin 2% ointment or cream to crusted areas tds
    Cefalexin 25 mg/kg po tds if widespread or large lesions

    5 days


    Mild cellulitis

    Cefalexin 25 mg/kg po tds

    5 days


    Moderate cellulitis

    A trial of high-dose oral antibiotics with close review may be considered:

    Cefalexin 33 mg/kg po tds (max 1g)

    Consider Ambulatory/Hospital-in-the-Home (HITH) if available:
    Ceftriaxone 50mg/kg IV daily (max 2g)
    Cefazolin 50mg/kg IV bd (max 2g)

    5 - 10 days

    If oral antibiotics not tolerated or no improvement after 48 hours, manage as per severe cellulitis
    When improving, switch to oral antibiotics as per mild cellulitis

    Severe cellulitis
    Staphylococcal scalded skin syndrome

    Flucloxacillin 50mg/kg (max 2g) IV 6H
    (if rapidly progressive consider adding Clindamycin 10mg/kg (max 600mg) IV 6H)


    5 - 10 days

    Consider early discharge to HITH once stable. When improving, switch to oral antibiotics as per mild cellulitis

    Necrotising Fasciitis

    Vancomycin and Meropenem 20mg/kg IV (max 1g) 8H
    Clindamycin 10mg/kg (max 600mg) IV 6H

    Urgent referral to surgical team for debridement
    Seek specialist advice for antibiotics
    Consider IVIg

    Mammalian bites (uninfected / prophylactic)

    Often do not need prophylactic antibiotics. When indicated*:
    80mg/mL Amoxicillin oral liquid (7:1)
    22.5mg/kg (max 875mg) po bd

    5 days


    Mammalian bites (established infection)

    80mg/mL amoxicillin oral liquid (7:1)
    22.5mg/kg (max 875mg) po bd
    If unable to tolerate oral antibiotics:
    25mg/kg (max 1g) IV 6-8H  

    5 days (extend if severe, penetrating, involving deep tissues)

    Seek specialist advice

    Waterborne skin infections – seawater or fresh water

    Cefalexin 25mg/kg po tds and Ciprofloxacin 10mg/kg (max 500mg) po bd 
    Trimethoprim/sulfamethoxazole 8/40mg/kg (max 320/1600mg) po bd

    5 - 10 days

    Clean and debride wound as needed
    Prophylactic antibiotics are not recommended

    *Indications for prophylactic antibiotics in a Mammalian bite:

    • Presentation delayed by >8 hours
    • Puncture wound unable to be adequately debrided
    • Bite on hands, feet, face
    • Involves deep tissues (e.g. bones, joints, tendons)
    • Involves an open fracture
    • Immunocompromised patient
    • Cat bites

    Suggested antibiotic therapy where MRSA is suspected

    Antimicrobial recommendations may vary according to local antimicrobial susceptibility patterns; please refer to local guidelines



    Total duration


    Mild cellulitis

    Trimethoprim/sulfamethoxazole 8/40mg/kg (max 320/1600mg) po bd
    Clindamycin 10mg/kg (max 450mg) po 6H

    5 days


    Moderate cellulitis

    A trial of oral antibiotics with close review may be considered
    Vancomycin IV


    When improving, switch to oral antibiotics as per mild cellulitis

    Severe cellulitis
    Staphylococcal scalded skin syndrome

    Vancomycin IV
    Clindamycin 10mg/kg (max 600mg) IV 6H

    When improving, switch to oral antibiotics as per mild cellulitis


    Risk factors for MRSA infection:

    • Residence in an area with high prevalence of MRSA, e.g. Northern Territory, remote communities in northern Queensland
    • Previous colonisation or infection with MRSA (particularly recent)
    • Aboriginal and Torres Strait Islander or Pacific Islander child

    Consider consultation with local paediatric team when:

    • No improvement or deterioration after 24 - 48 hours of therapy
    • Consider surgical opinion if deep abscess or necrotising fasciitis suspected

    Consider transfer when:

    Child requires care above the level of comfort of local hospital

    For emergency advice and paediatric or neonatal ICU transfers, see Retrieval Services.

    Consider discharge when:

    Able to tolerate oral antibiotics

    Parent Information
    Staphylococcal infections
    Bleach Baths

    Last Updated March 2020

  • Reference List

    1. Baguley D, Lim E, Bevan A, et al. Prescribing for children - taste and palatability affect adherence to antibiotics: a review. Archives of disease in childhood 2012;97(3):293-7
    2. BMJ Online. Diagnosis and management of cellulitis. (viewed 25 November 2019)
    3. Ibrahim LF, Hopper SM, Orsini F, Daley AJ, Babl FE, Bryant PA. Efficacy and safety of intravenous ceftriaxone at home versus intravenous flucloxacillin in hospital for children with cellulitis (CHOICE): a single-centre, open-label, randomised, controlled, non-inferiority trial. The Lancet Infectious diseases 2019;19(5):477-86
    4. Jamal N, Teach SJ. Necrotizing fasciitis. Pediatric emergency care 2011;27(12):1195-9
    5. Kilburn SA, Featherstone  P, Higgins  B, Brindle  R. Interventions for cellulitis and erysipelas. Cochrane Database of Systematic Reviews 2010, Issue 6. Art. No.: CD004299. DOI: 10.1002/14651858.CD004299.pub2
    6. Sullivan T, de Barra E. Diagnosis and management of cellulitis. Clinical Medicine. 2018;18(2):160–163
    7. Therapeutic Guidelines. Acute Wound Infections. (viewed 30 September 2019)