Impetigo

Impetigo is a highly contagious skin infection, common in children, that most commonly occurs around the nose and mouth, but can affect the skin anywhere on the body.

Cause and symptoms

Impetigo is caused by bacteria (usually streptococci or staphylococci) entering areas of broken skin. The skin reddens and small, fluid-filled blisters appear. The blisters tend to burst, leaving moist, weeping areas that dry to leave honey-coloured or golden crusts. In severe cases, there may be swelling of the lymph nodes in the face or neck and fever.

Treatment and prevention

Treatment is with topical (locally administered) antibiotic drugs unless the condition is widespread, in which case oral antibiotics are usually given. As the condition is highly contagious, to prevent the spread of the infection, towels, flannels, and pillowcases should not be shared. Children should not go to school or mix with others until they have been treated and the condition has cleared up.

Impetigo pictures

Impetigo in more detail - technical

This is a superficial infection confined to the epidermis caused by Staphylococcus aureus  or β-haemolytic streptococci, the cause depending, to some extent, on geography and climate. In temperate zones, the normal cause is S. aureus but in the tropics β-haemolytic streptococci are more common, although in about 20% of cases these organisms can both be isolated from lesions, indicating a mixed infection. In most cases this is a primary infection but it may also be secondary to other skin conditions such as eczema or scabies. Impetigo is common in primary care in temperate climates, its incidence accounting for about 20 per 1000 person years in the under 18 population, and there is some evidence to suggest that this incidence is increasing. However, it can also be found in other groups where close contact is likely, e.g. military recruits. It is more common in summer than winter. Pyoderma is more common in the tropics where it is often secondary to another skin disease such as scabies.

In most European countries and the United States of America, where S. aureus predominates, some cases present with blistering lesions (bullous impetigo—see below). S. aureus produces exfoliotoxins that cleave the human cell adhesion molecule desmoglein 1(Dsg1). This results in the formation of an epidermal bulla similar to the blister formation in pemphigus foliaceus where Dsg1 is the target of an autoantibody. Very extensive blistering occurs in the childhood infection staphylococcal scalded skin syndrome (SSSS). Production of exfoliotoxin A is more associated with bullous impetigo and exfoliotoxin B with SSSS.

Impetigo usually presents with itching or discomfort in the affected area, which becomes red and the surface glazed and with a golden-coloured serous ooze. As stated previously, S. aureus infections may also result in bullous lesions (bullous impetigo). Impetigo is most common in children and often develops on the face or trunk, but lesions can be found elsewhere. Infected lesions may also develop from localized wounds, or insect bites, or around areas where the carriage rate is high, e.g. near eczematous plaques, or close to the nose. Patients are generally well and usually show no internal signs of infection such as fever.

Treatment consists of flucloxacillin or erythromycin, although, if the lesion is very localized, a topical antibiotic such as fusidic acid or mupirocin can be used (short-term). Impetigo is contagious particularly among children at school or in families and therefore close contacts should be screened for infection. There is little evidence to support the use of antiseptics in primary treatment, however logical. Hand washing, though, has been shown to reduce the risk of impetigo.

If the lesions penetrate deeper into the dermis they appear as well defined but localized ulcers know as ecthyma. These occur, particularly, in hot climates or where the site of infection is occluded by tight clothing. Ecthyma may also complicate other skin conditions, e.g. chickenpox. It is treated with systemic antibiotics.

Staphylococcus aureus and impetigo

The most superficial Staphylococcus aureus infections are impetigo, folliculitis, and cellulitis. Impetigo is limited to the epidermis, folliculitis to the hair follicles, and cellulitis to the dermis and/or the subcutaneous fat. Impetigo can appear as small round honey-crusted lesions on the skin, primarily on exposed areas. Impetigo typically is caused by streptococci; in the United Kingdom, S. aureus is an infrequent cause. However, bullous impetigo is a clinical variant (caused by S. aureus phage type 71), reported in up to 10% of impetigo cases. Initially, the lesions can be vesicles that enlarge into bullae containing clear or yellow fluid.

Treatment of impetigo (Table 7.6.4.2) should reflect local antibiotic resistance patterns. Topical therapy may be effective for limited disease, though EMRSA-16, one of two predominant MRSA types in the United Kingdom, often shows high-level mupirocin resistance. Systemic therapy should be used in patients with impetigo who have many lesions or who fail topical therapy. In areas where CA-MRSA prevalence exceeds 10%, initial therapy should be directed by local susceptibility patterns.

Table 1 Therapy of impetigo and mild soft tissue lesions caused by Staphylococcus aureus
Therapy Drug Dosage Duration
Topical Mupirocin 2% ointment TID 14 days
Fusidic acid 2% cream TID
Oral For penicillin-susceptible S. aureus: 5 days
Amoxicillin 250–500 mg PO TID or 875 mg PO BID
Amoxicillin + clavulanate 250–500 mg PO TID or 875 mg/125 mg PO BID
Penicillin VKa 250–500 mg PO QID
For methicillin-susceptible S. aureus:
Dicloxacillina 250 mg PO QID
Cefalexin 500 mg PO QID
For methicillin-resistant S. aureus (or b-lactam allergy):
Clindamycin (Erys, Clins, or D-test negative) 300–450 mg PO QID
Trimethoprim/sulfamethoxazole 1–2 double-strengthb tablets PO BID
Doxycycline 100 mg PO BID
Minocycline 100 mg PO BID
Linezolid 600 mg po BID

BID, twice daily; Clins, clindamycin-sensitive; D, double-disc diffusion; Erys, erythromycin-sensitive; PO, by mouth; QID, four times daily; TID, three times daily.

a First-line agent.

b 160 mg trimethoprim and 800 mg sulfamethoxazole in a double-strength tablet.

Streptococcal skin and soft tissue infections - impetigo

Pyoderma/impetigo

Almost any purulent lesion of the skin can yield S. pyogenes, sometimes with Staphylococcus aureus. Such lesions include impetigo, infected cuts and lacerations, insect bites, scabies, intertrigo, and ecthyma. S. pyogenes often causes secondary infection in varicella, occasionally with resultant bacteraemia. The term pyoderma is used synonymously with impetigo for discrete purulent apparently primary infections of the skin that are prevalent in many parts of the world, especially in children. These lesions are initially papules, then vesicular with surrounding erythema, and finally pustules with crusting exudate; they may be localized to one part of the body or generalized. Outbreaks of impetigo can occur among adults subject to skin trauma, such as rugby football players (scrumpox), and streptococcal infection of cuts on the hands and forearms are an occupational hazard for workers in the meat trade. Epidemics of impetigo can occur in day care centres, prisons, and schools. Ecthyma is an ulcerated form of impetigo in which ulceration extends into the dermis. In recent times, approximately 50% of cases of impetigo are caused by Staphylococcus aureus.