Impetigo

Definition/diagnostic criteria Impetigo is a highly contagious skin infection primarily caused by Staphylococcus aureus and sometimes by Streptococcus pyogenes. It is characterised by the presence of pustules and honey-coloured crusts. Impetigo is divided into two types: non-bullous (crusted) and bullous (blistering). Non-bullous impetigo, caused by both staphylococci and streptococci, is more common and presents with pustules that rapidly evolve into honey-coloured crusted erosions. Bullous impetigo, primarily caused by S aureus, presents with larger blisters due to toxin-mediated cleavage of the epidermal layer.

Epidemiology Impetigo is common and predominantly affects children, particularly those aged 2 to 5 years. The annual incidence is around 2.8% in children up to 4 years of age. It is more common in warm, humid climates and often occurs in outbreaks within family groups or school settings. The prevalence is influenced by socio-economic factors and overcrowding.

Diagnosis
Clinical features: The diagnosis is primarily clinical.

• Non-bullous impetigo presents with rapidly rupturing pustules, leaving golden-yellow crusts, typically around the nose and mouth.
• Bullous impetigo features larger, fluid-filled blisters on the trunk or extremities, which may rupture, leaving a thin brown crust.
• Lymphadenopathy may be present nearby the affected areas.

Investigations: Investigations are not usually necessary for typical cases of impetigo.

• If the diagnosis is uncertain, or if the infection is recurrent or widespread, swab cultures may be taken for bacteriology.
• Typical abnormalities in such cases would show a predominance of S aureus and/or S pyogenes.

Treatment

• Topical hydrogen peroxide: Consider hydrogen peroxide 1% cream (two or three times daily for five days) for patients who are otherwise well and not at risk of complications.
• Topical antibiotics: For localised, non-bullous impetigo, a topical antibiotic such as fusidic acid is recommended for five days. Mupirocin can be considered if fusidic acid is not effective or if the strain is resistant.
• Oral antibiotics: Recommended in cases of widespread non-bullous impetigo, bullous impetigo, or if topical treatment is impractical. Flucloxacillin is the first choice, reflecting its efficacy against S aureus, for a duration of seven days. For penicillin-allergic patients, clarithromycin or erythromycin can be used. The treatment should be reassessed if there is no improvement within two to three days.

Prognosis Impetigo generally has a good prognosis and is self-limiting. Complications are rare but can include cellulitis, scarlet fever or, in severe cases, sepsis. Recurrence is possible, particularly in individuals with close contact with infected persons or those with poor hygiene practices. Good hygiene and avoiding sharing personal items are important to prevent the spread of impetigo.