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Author: Dr Kate Quirke, Senior House Officer, Rotorua Hospital, New Zealand. Copy edited by Gus Mitchell. March 2022. Previous author: Hon A/Prof Amanda Oakley, Dermatologist, Waikato Hospital, New Zealand.


What is impetigo?

Impetigo is a common, superficial, highly contagiousbacterialskininfectioncharacterised bypustulesand honey-colouredcrustederosions.

It affects the superficial layers of theepidermisand is typically caused byStaphylococcus aureusandStreptococcus pyogenes(Group A beta –haemolyticstreptococci (GABHS)). It can be classified into non-bullous(also known as ‘school sores’) and bullous impetigo.Ecthymais a deep form of impetigo causing deeper erosions of the skin into thedermis.

Secondary infection of wounds or other skinlesionswith the samepathogensis called ‘impetiginisation’.

For more images of impetigo,click here.

Who gets impetigo?

Impetigo is most common in young children but can occur at any age. It is usually transmitted through direct contact.

Risk factors which maypredisposean individual to impetigo include:

What causes impetigo?

Impetigo is caused byStaphylococcus aureus, and less commonlyStreptococcus pyogenes.

Non-bullous impetigo

  • Caused by eitherStaphylococcus aureus,Streptococcus pyogenes, or bothbacteriaconjointly.
  • Intact skin is usually resistant to colonisation from bacteria. Disruption in skin integrity allows for invasion of bacteria via the interrupted surface.

Bullous impetigo

  • Due toStaphylococcus aureuswhich producesexfoliativetoxins(exfoliatins A and B).
  • Exfoliative toxins targetintracellularadhesionmolecules(desmoglein– 1) present in theepidermalgranularlayer.
  • Results in dissociation of epidermal cells which causes blister formation.
  • Can occur on areas of intact skin.

What are the clinical features of impetigo?

Non-bullous impetigo

  • Most commonly found on the face or extremities but skin on any part of the body can be involved.
  • Begins with a singleerythematousmaculewhich evolves into apustuleorvesicle.
  • Pustule or vesicle ruptures releasingserouscontents which dries leaving a typical honey-colouredcrust.
  • Minimal or no surroundingerythema.
  • Can spread rapidly with satellite lesions due toautoinoculation.
  • “Kissing lesions” arise where two skin surfaces are in contact.
  • Patients are typically otherwise well; they may experience someitchingand regionallymphadenopathy.

Bullous impetigo

  • Usually found on the face, trunk, extremities, buttocks, andperinealregions.
  • Can spread distally due to autoinoculation.
  • Present as quickly appearing superficial, small or large thin roofedbullaewhich tend to spontaneously rupture and ooze yellow fluid leaving a scaley rim (collarette).
  • More likely to havesystemicsymptoms ofmalaise,fever, and lymphadenopathy.

How do clinical features vary in differing types of skin?

The initial erythematous macule in non-bullous impetigo may be more difficult to see on darker skin tones.

什么是合并cations of impetigo?

How is impetigo diagnosed?

  • 脓疱病通常是一种临床诊断based on the features described above.
  • A skin swab forcultureand sensitivity may be beneficial if the impetigo isrecurrent,widespreador there is concern ofMRSA infection.
  • Nasal swabs should be carried out in recurrent infection as they can identify staphylococcal nasal carriage which requires specific management.
  • Rarely abiopsymay be indicated if the diagnosis is unclear (in particular for bullous impetigo) or if it isrefractoryto treatment.
  • Histologicalfeatures are characteristic.

What is thedifferential diagnosisfor impetigo?

What is the treatment and prevention of impetigo?

General measures

  • Regular gentle cleansing; removal of honey-coloured crusts.
  • Practice good hand hygiene and keep fingernails cut short.
  • Cover the affected areas with watertight dressing to prevent spread.

Specific measures


  • Forlocalisednon-bullous impetigo, application ofantiseptic2–3 times per day for 5–7 days is recommended (e.g. hydrogen peroxide 1%creamor povidone — iodine 10%ointment).
  • Topical antibiotics such asfusidic acidormupirocin是有效的治疗non-bullous脓疱病,何wever, their use may not be recommended in some countries due to bacterial resistance.
  • Topical antibiotics can be considered when antiseptic treatment has not worked or is not appropriate (e.g. impetigo around the eyes).
    • Fusidic acid is first-line.
    • Mupirocin use is often reserved for possible MRSA infection.

Oral antibiotics

  • Recommended in bullous impetigo, widespread non-bullous impetigo (>3 lesions), when topical treatment fails, a person is at high risk of complications, or when a person is systemically unwell.
  • Oralflucloxacillinis often the first line antibiotic of choice.
  • Alternatives may include trimethoprim + sulfamethoxazole or erythromycin (eg, if penicillin allergic or for MRSA infection).

Preventative measures

  • Avoid touching affected areas.
  • Practice good hand hygiene; wash hands before and after applyingcreams.
  • Use a clean cloth each time to wash and dry affected areas.
  • Do not share towels or face cloths.
  • Clothing and bedding should be changed daily; wash using hot temperatures.
  • Avoid close contact with others — school/nursery children should stay home until lesions have crusted over, or they have received at least 24 hours of treatment.

What is the outcome for impetigo?

Impetigo is usuallyself-limitingwithout serious complications. Without treatment, impetigo usually heals in 2–3 weeks; with treatment lesions resolve within 10 days.

Postinflammatoryhypopigmentationorhyperpigmentationmay occur but scarring is uncommon.


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  • Cole C, Gazewood J: Diagnosis and Treatment of Impetigo. Am Fam Physician. 2007;75(6):859–64.Journal
  • Hartman-Adams H, Banvard C, Juckett G. Impetigo: diagnosis and treatment. Am Fam Physician. 2014;90(4):229–35.Journal
  • Hoffmann TC, Peiris R, Glasziou P, Cleo G, Mar CD. Natural history of non-bullous impetigo: a systematic review of time to resolution or improvement without antibiotic treatment. Br J Gen Pract. 2021;71(704):e237–42.Journal
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  • Williamson D, Ritchie S, Best E, Upton A, Leversha A, Smith A, Thomas M. A bug in the ointment: topical antimicrobial usage and resistance in New Zealand. N Z Med J. 2015;128:103–9.Journal

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