Impetigo is a very common superficial infection of the skin. It can be divided into non-bullous and bullous forms. The non-bullous types represent the majority of cases. The infecting organism for the more common non-bullous type is usually Staphylococcus aureus or Streptococcus pyogenes. Over a period of 50 years there has been a considerable move from streptococci to staphylococci as the principal causative organisms. Meticillin-resistant S. aureus (MRSA) is another increasingly common causative organism for non-bullous impetigo. Usually the predisposing factor is a breach of the skin but bullous impetigo may affect intact skin and is almost invariably caused by S. aureus.
It is also occasionally classified as primary or secondary, where primary impetigo occurs in intact skin, and secondary impetigo in skin already damaged by another condition.
Impetigo is a common condition. It most often affects children although it can occur at any age. Annual incidence in the UK is estimated to be 2.8% of children under the age of 4 and 1.6% of children aged 5-15. Global estimates suggest around 162 million children have impetigo at any one time, prevalence being highest in tropical areas and underprivileged communities. The streptococcal form is more common in warmer and more humid climates. There is some evidence for seasonal variation, with staphylococcal infections being more common in warmer months.
Risk factors include poor hygiene and skin conditions that lead to a break in the protective layers. Atopic eczema is a common risk factor; others include bites, trauma to the skin, scabies, chickenpox, burns and contact dermatitis.
Non-bullous lesions usually start as tiny pustules or vesicles that evolve rapidly into honey-coloured crusted plaques that tend to be under 2 cm in diameter. It is usually on the face (particularly around the mouth and nose) and may also be on the extremities where bites, abrasions, lacerations, scratches, burns or trauma have occurred. It spreads rapidly. Satellite lesions may occur as a consequence of autoinoculation. There may be some itching. There is little or no surrounding erythema or oedema. Regional lymph nodes are often enlarged.
Bullous lesions have a thin roof and tend to rupture spontaneously. They are usually on the face, trunk, extremities, buttocks, or perineal regions. They are more likely to occur on top of other disease like atopic eczema. There is little erythema and usually no regional lymphadenopathy. Bullous lesions are more common in neonates but can occur at any age. This type is more likely to be painful and may be associated with systemic symptoms of malaise.
This begins as a non-bullous impetigo but ulcerates and becomes necrotic. It is deeper and may occur with lymphadenitis.
- Contact dermatitis.
- Various viral skin infections including herpes simplex, herpes zoster and varicella-zoster viruses.
- Bullous pemphigoid.
- Atopic eczema.
- Stevens-Johnson syndrome.
- Toxic epidermal necrolysis.
Diagnosis is usually purely clinical but a swab for culture and sensitivity may be useful if:
- The impetigo is extensive or severe.
- MRSA is suspected.
- The impetigo is recurrent or failing to respond to treatment. (Take nasal swabs if there is recurrent impetigo to exclude nasal staphylococcal colonisation. Use Naseptin® to eradicate it if found.)
Advise good hygiene measures:
- Keep the affected area(s) clean.
- Wash hands after touching affected area(s).
- Avoid sharing of towels and bathwater.
- Avoid scratching the affected area. Keep fingernails short and clean.
Public Health England (PHE) advises that children should stay off school (or adults should stay off work) until lesions are all dry and scabbed over, or the affected person has been on antibiotics for 48 hours.
A Cochrane review found good evidence for efficacy of topical mupirocin and fusidic acid, and that they were as effective as oral antibiotic treatment. There was no evidence for topical disinfectants being effective therapy. Opinion varies as to whether crusts should be soaked off prior to applying topical treatment. The National Institute for Health and Care Excellence (NICE) Clinical Knowledge Summary on impetigo advises that fusidic acid is used first-line in localised infections, three times a day for seven days. Mupirocin should be reserved for cases where MRSA is the causative organism, to avoid resistance.
Oral antibiotics are only needed when infection is extensive or resistant to topical treatment, or causing systemic symptoms. A seven-day course is recommended. Flucloxacillin is recommended as first-line treatment when oral antibiotics are required. Clarithromycin or erythromycin are recommended as second-line for those who are allergic to penicillin, with clarithromycin being preferred, as side-effects are less common.
Bullous infection usually requires oral antibiotics.
If the causative organism is a group A beta-haemolytic streptococcus then rare complications such as scarlet fever or glomerulonephritis may occur. However, impetigo is most often caused by staphylococci.
Mortality in infants with staphylococcal scalded skin syndrome is low but it can be as high as 63% in adults. It represents a serious clinical challenge and will usually require admission to hospital.
The condition usually resolves without complications but it is highly contagious and may recur due to re-infection from family members with shared towels, etc.
Measures described include:
- Avoidance of contact with infected individuals. Those affected should avoid school/nursery/work as above and cover the lesions where possible. They should use their own towels, flannels, clothing, etc, all of which should be washed separately and regularly.
- Keeping wounds clean.
- Teaching good personal hygiene. This is important for parents, carers and health professionals. For example: wash hands after contact with lesions or infected patients (with antibacterial soap and water or waterless antibacterial cleansers).
- Treating pre-existing underlying skin diseases, such as atopic dermatitis (for example, antihistamines and topical steroids reduce scratching and hence skin damage and spread).
- For patients with recurrent impetigo, asymptomatic family members and S. aureus nasal carriers, try measures to reduce colonisation of the nose and spread, such as the use of Naseptin®. Mupirocin may also be used (twice a day for five days applied to each nostril).
- For MRSA screening and eradication, refer to local guidelines.
Further reading and references
; DermNet NZ
; Primary Care Dermatology Society (PCDS)
; NICE CKS, July 2015 (UK access only)
; The Global Epidemiology of Impetigo: A Systematic Review of the Population Prevalence of Impetigo and Pyoderma. PLoS One. 2015 Aug 2810(8):e0136789. doi: 10.1371/journal.pone.0136789. eCollection 2015.
; Seasonality of staphylococcal infections. Clin Microbiol Infect. 2012 Oct18(10):927-33. doi: 10.1111/j.1469-0691.2012.03955.x.
; Public Health England
; Public Health England (September 2017)
; Interventions for impetigo. Cochrane Database Syst Rev. 2012 Jan 181:CD003261. doi: 10.1002/14651858.CD003261.pub3.
; Staphylococcal scalded skin syndrome: diagnosis and management in children and adults. J Eur Acad Dermatol Venereol. 2014 May 20. doi: 10.1111/jdv.12541.