Impetigo

Contagious impetigo or impetigo vulgaris is a superficial bacterial skin infection, frequent in childhood.

Impetigo is most common in the summer months, in humid climates and in atopic subjects. It usually results from small breaks in the skin. There are sporadic forms and epidemic forms which arise in child communities (school, nursery). The infection is usually transmitted exogenously by sick subjects but also by healthy carriers of the bacteria, most commonly located in the nasal vestibule, pharynx or more rarely on the hands. Two forms are recognised: non-bullous caused by Streptococcus pyogenes, often together with Staphylococcus aureus, and bullosa caused by Staphylococcus aureus, due to the production of an exfoliative toxin.

Signs and symptoms

It is manifested by one or several erythematous patches on which vesicles or blisters with a very thin roof form, the contents of which become purulent and, after drying, give rise to a superficial, yellowish and lightly adherent crust, called honey-coloured crust. Under the crust the surface is red and highly exudative. The bullous form of impetigo is manifested with flaccid blisters which rupture and leave superficial erosions, with a shiny surface. The bullous lesions are sometimes large (phlyctenular giant impetigo). Its typical locations are the uncovered parts such as the face, hands, limbs and scalp. It spreads by autoinoculation, subsequently also affecting the covered parts.

Diagnosis

Diagnosis is generally clinical. In cases of doubt, or if there is no response to therapy, bacteriological tests are performed: culture, with antibiogram or, more rarely, Polymerase Chain Reaction (PCR).

Course

The course is acute. In some cases there is also lymphangitis and regional lymphoadenitis with tendency to suppuration. Healing takes place with a return to original condition, although there may remain temporary dyschromic sequelae. There are no subjective symptoms.

Particular forms

Neonatal impetigo: It is an infection usually acquired in the first weeks of life, and the aetiological agent is Staphylococcus aureus. The bullous lesions due to the local action of the toxin usually start in the periumbilical, perineal and neck regions. At this stage in life, complications such as pneumonia, abscesses and osteomyelitis are more common. Moreover, due to the neonate’s limited ability to eliminate the toxin, the infection may spread and give rise to a generalised exfoliative dermatitis, Staphylococcal Scalded Skin Syndrome (SSSS).

Impetiginisation is the bacterial superinfection of pre-existing dermatoses characterised by intense pruritus and scratching such as atopic dermatitis, scabies and pediculosis. Excoriations are the point of entry of the pathogenic bacterium.

Differential diagnosis

For delimited forms, differential diagnosis is with herpes simplex and eczema, and for diffuse forms with autoimmune bullous diseases.

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