Impetigo

Impetigo is a common bacterial infection affecting the superficial layers of the skin. It is highly contagious and primarily caused by Staphylococcus aureus and Streptococcus pyogenes.

The infection is most prevalent in children, especially those who attend day care or school, and typically resolves within three weeks without scarring. However, complications such as cellulitis and poststreptococcal glomerulonephritis can occur.

Signs and Symptoms

Contagious Impetigo

The most common form, also known as nonbullous impetigo, begins as red sores near the nose or mouth. These sores break open and leak pus or fluid, forming honey-coloured scabs. This type is generally not painful but can be itchy. Swollen lymph nodes may be present, although fever is rare. Scratching can spread the infection to other body parts.

Bullous Impetigo

This form is primarily seen in children under two years old. It involves painless, fluid-filled blisters on the arms, legs, and trunk. These blisters are surrounded by red and itchy skin. After rupturing, they form yellow scabs.

Ecthyma

Ecthyma is a more severe form of impetigo that penetrates deeper into the dermis, producing painful fluid- or pus-filled sores. These sores become ulcers and form hard, thick, grey-yellow scabs, often leaving scars. Swollen lymph nodes may accompany this form.

Causes and Transmission

Impetigo is mainly caused by Staphylococcus aureus, and occasionally by Streptococcus pyogenes. It spreads through direct contact with infected lesions or nasal carriers. The incubation period is 1–3 days for Streptococcus and 4–10 days for Staphylococcus. Scratching can also facilitate the spread of the infection.

Diagnosis

Diagnosis is typically based on the clinical appearance of the lesions, which are characterised by honey-coloured scabs. If the diagnosis is unclear, a bacterial culture may be performed to test for antibiotic resistance.

Differential Diagnosis

Conditions that may mimic impetigo include contact dermatitis, herpes simplex virus, discoid lupus, scabies, burns, and necrotising fasciitis.

Prevention

Preventing impetigo involves maintaining good hygiene, such as regular hand washing and cleaning injuries promptly. Infected individuals should avoid close contact with others and refrain from sharing personal items like clothing or linens. Children can return to school 24 hours after starting antibiotic treatment if their lesions are covered.

Treatment

Treatment typically involves antibiotics, either topical or oral. Mild cases may be treated with mupirocin or fusidic acid ointments. More severe cases may require oral antibiotics such as dicloxacillin, flucloxacillin, or erythromycin. In cases of methicillin-resistant Staphylococcus aureus (MRSA), alternatives like doxycycline, clindamycin, or trimethoprim-sulphamethoxazole may be used. Hydrogen peroxide 1% cream is recommended for localised nonbullous impetigo in otherwise healthy individuals to reduce antibiotic resistance.

Prognosis

Without treatment, impetigo usually resolves within three weeks. However, complications such as cellulitis and poststreptococcal glomerulonephritis can occur, although rheumatic fever does not appear to be related.

Epidemiology

Impetigo affects approximately 140 million people globally, with higher prevalence in low- to middle-income countries and tropical climates. Children under four years old are particularly susceptible.

History

Impetigo was first described by the English dermatologist William Tilbury Fox in 1864. The name originates from the Latin word impetere, meaning "to attack." Before antibiotics, the infection was treated with gentian violet, an antiseptic.

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Self-assessment MCQs (single best answer)

What is the primary cause of impetigo?

What is the most common form of impetigo?

Which population is most affected by impetigo?

What is the incubation period for _Staphylococcus aureus_ when causing impetigo?

Which of the following is NOT a recommended treatment for impetigo?

Which form of impetigo involves painful fluid- or pus-filled sores that become ulcers?

Which of the following is a common complication of impetigo?

Which antibiotic is recommended for treating methicillin-resistant _Staphylococcus aureus_ (MRSA)?

Which of the following is a key preventive measure for impetigo?

Who first described impetigo, and in what year?