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 about 70%. The infecting organism is usually Staphylococcus aureus or a beta-haemolytic streptococcus, although other organisms or mixed flora may be implicated. Over the past 50 years there has been a considerable move from streptococci to staphylococci as the principle causative organisms.
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.
Another classification is as primary and secondary impetigo. In the latter it occurs on top of other dermatological disease or extensive breaks in the skin.

Epidemiology

It is extremely common and occurs in all parts of the world but precise figures are not available. It is more common in hot areas where sweating can macerate the skin and biting insects may also break it. In the UK impetigo seems to be most common in late summer.¹
Impetigo is most often found in preschool children but is also quite common in young adults, especially in military training environments where a number of factors may be predisposing. The elderly are also more susceptible to skin infections.²

Risk factors

Poor hygiene and skin conditions that lead to a break in the protective layers.

Presentation

• Non-bullous lesions usually start as tiny pustules that evolve rapidly into honey-coloured crusted plaques that tend to be under 2 cm in diameter. It is usually on exposed areas of the face and extremities where bites, abrasions, lacerations, scratches, burns or trauma have occurred. It spreads rapidly. 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.

Other varieties of impetigo described are:

• Impetigo contagiosa. This is a superficial, intraepidermal, vesiculopustular infection (and the most common skin infection in children).
  
  
  
  
  
  
  
  
  
  
  
  
• Bullous impetigo is a toxin-mediated erythroderma and involves the sloughing off of the epidermal layer of the skin. There may be large areas of superficial skin loss.
  
  
  
  
  
• Common impetigo. This term is usually applied to infection occurring in pre-existing wounds. Impetigo can also present as folliculitis, which is considered to be impetigo of the hair follicles caused by S. aureus. This is an example in the axilla:
  
  
• Ecthyma is a deeper, ulcerated impetigo infection, often occurring with lymphadenitis.

Differential diagnosis

• Contact dermatitis.
• Scabies.
• Various viral skin infections including herpes simplex, herpes zoster and varicella-zoster viruses.
• Bullous pemphigoid.

Investigation

Diagnosis is usually purely clinical but a swab for culture and sensitivity may be useful.

Management

• Local treatment involves cleansing, removal of crusts, and frequent application of wet dressings.
• If the condition is localised, topical mupirocin or fusidic acid is applied to affected skin.^3,4 For nasal carriers, mupirocin or chlorhexidine and neomycin cream may be used. Mupirocin should not be used for more than 10 days for fear of development of resistance (British National Formulary advice).
• Oral flucloxacillin or erythromycin may be required. Co-amoxiclav, clarithromycin and azithromycin are alternatives, but cephalosporins and cephamycins vary in their activity against staphylococci.
• Community-acquired methicillin-resistant S. aureus (MRSA) is uncommon in children but can usually be treated with clindamycin or co-trimoxazole (depending on sensitivities).⁵
• Emollients in bath water may help improve the integrity of the skin but antiseptics are so highly diluted that they are unlikely to be effective
• If itching is a problem then oral antihistamines may help to prevent scratching which spreads the infection. Topical antihistamines should be avoided because of risk of allergy. The old-fashioned, sedating types are required as the efficacy is related to sedation rather than antihistamine effect.

Complications

• Complications of group A beta-haemolytic streptococci like scarlet fever or glomerulonephritis are much rarer nowadays but also impetigo is most often caused by staphylococci.
• Cellulitis, lymphangitis, suppurative lymphadenitis, and staphylococcal scalded skin syndrome may occur in as many as 10% of patients with impetigo. Cellulitis rarely follows bullous impetigo.
• Mortality in infants with staphylococcal scalded skin syndrome is low but it can be as high as two thirds in adults.⁶ It represents a serious clinical challenge and will usually require admission to hospital.

Prognosis

The condition usually resolves without complications but it is highly contagious and may recur due to reinfection from family members with shared towels, etc.

Prevention⁷

Measures described include:

• Avoidance of contact with infected individuals.
• Keeping wounds clean.
• Teaching good personal hygiene. This is important for parents, carers and health professionals. For example:
  Wash hands after contacting lesions or infected patients (with antibacterial soap and water or waterless antibacterial cleansers).
• Treating traumatised skin with mupirocin (because this has been shown to decrease the rates of impetigo spread).
• Looking for asymptomatic bacterial carrier states in, for example, the staff of hospital nurseries.
• 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 (for example, by using 2% mupirocin cream or ointment applied inside the nostril 3 times per day for 5 days each month).
• Patients who are chronic nasal carriers can also be treated with clindamycin or rifampin plus dicloxacillin (an alternative to flucloxacillin not licensed in the UK).
• Advising patients about improving environmental conditions (for example, air conditioning and general room and surface cleanliness).

Historical

• First named staphylococcus by Sir Alexander Ogston in 1881 in recognition of the grape-like clusters of bacteria he observed in pus from human abscesses.
• Rosenbach described the 2 pigmented colony types of staphylococcus in 1884, naming then S. aureus and S. albus (now known as S. epidermidis). He also showed that S. aureus was responsible for wound infections and furunculosis.
• The streptococcus was first described by Billroth (the famous surgeon who introduced the concept of audit) in 1874, Friedrich Fehleisen isolated the bacteria in 1883, and was named Streptococcus pyogenes by Rosenbach in 1884.
• William Tilbury Fox (1836-1879) wrote a classical description of impetigo contagiosa which appeared in Wilson's Journal. William Wilson (1809-1884) was a self-taught dermatologist, who famously transported Cleopatra's needle at his own expense from Alexandria to the Thames embankment.

Document references

1. Loffeld A, Davies P, Lewis A, et al; Seasonal occurrence of impetigo: a retrospective 8-year review (1996-2003). Clin Exp Dermatol. 2005 Sep;30(5):512-4. [abstract]
2. Laube S; Skin infections and ageing. Ageing Res Rev. 2004 Jan;3(1):69-89. [abstract]
3. George A, Rubin G; A systematic review and meta-analysis of treatments for impetigo. Br J Gen Pract. 2003 Jun;53(491):480-7. [abstract]
4. Sladden MJ, Johnston GA; Common skin infections in children. BMJ. 2004 Jul 10;329(7457):95-9.
5. Ladhani S, Garbash M; Staphylococcal skin infections in children: rational drug therapy recommendations. Paediatr Drugs. 2005;7(2):77-102. [abstract]
6. Patel GK; Treatment of staphylococcal scalded skin syndrome. Expert Rev Anti Infect Ther. 2004 Aug;2(4):575-87. [abstract]
7. Amini S; Impetigo (dermatology perspective), eMedicine, May 2010

Internet and further reading

• Lewis L; Impetigo (paediatric perspective), eMedicine, Mar 2010
• Ratz J; Impetigo (infectious diseases perspective), eMedicine, Nov 2009
• Rashid R; Impetigo (emergency medicine perspective). eMedicine, Jun 2010
• Impetigo, Clinical Knowledge Summaries (June 2009)

Acknowledgements