|

Impetigo

Last updated:

Overview

Impetigo is a common superficial bacterial skin infection due to Staphylococcus aureus or Streptococcus pyogenes, causing pustular lesions that can rupture and discharge a thin, yellow-coloured fluid that can dry and form a crust. This tends to occur on the face, especially around the mouth and nose.

Impetigo can be divided into two clinical entities:

  • Non-bullous impetigo – In around 70% of cases, no bullae are seen
  • Bullous impetigo – fluid-filled bullae are present that are >5mm in diameter

It can develop as a primary infection or as a secondary infection in people with pre-existing skin conditions such as eczema, chickenpox, and scabies.

Pathophysiology

Transmission is through direct contact with an infected person, but can also be indirect via contaminated objects. Bacteria enter via skin breaks (e.g. scratches, eczema etc.).

In bullous impetigo, Staphylococcus aureus can produce exfoliative toxins, which reduce epidermal cell adhesion, resulting in the formation of bullae.

Epidemiology

  • Impetigo is most common in young children
  • Incidence is higher in warmer weather
  • Bullous impetigo is less common and most reported in children <2 years old

Risk Factors

  • Breaks in the skin and pre-existing skin disease (e.g. scratches, eczema, scabies etc.)
  • Hot/humid weather
  • Poor hygiene
  • Overcrowding

Presentation

Non-bullous impetigo

Features of non-bullous impetigo include:

  • An erythematous macule that becomes a pustule/vesicle, which ruptures and releases material that dries, leaving a ‘honey-coloured’/‘golden’ crust
    • Upon drying, they can leave mild erythema which then fades
    • Where two skin surfaces are in contact, ‘kissing lesions’ can occur
    • Most commonly seen around the nose and mouth
    • They do not usually cause problems but may be itchy
  • Very contagious – can spread rapidly due to autoinoculation
  • Patients are otherwise well

Bullous impetigo

Features of bullous impetigo include:

  • A blister that can rupture and ooze yellow fluid
    • Most commonly seen on the face, trunk, extremities, perineal region, and buttocks
  • Patients may have systemic upset – including fever, malaise, and lymphadenopathy:
    • This is more common if large areas are affected
    • In infants, this can be widespread

Diagnosis

Impetigo is usually diagnosed clinically, however, in cases that are persistent, recurrent, or widespread, swabs of exudative material can be taken to screen for methicillin-resistant Staphylococcus aureus (MRSA).

Management

For limited and localised non-bullous impetigo:

  • 1st-line: hydrogen peroxide 1% cream – this was introduced in 2020 to reduce antibiotic resistance
  • If unsuitable/ineffective: topical fusidic acid or if resistance is suspected/confirmed topical mupirocin

For widespread non-bullous impetigo and not systemically unwell or at high-risk of complications:

  • 1st-line: oral flucloxacillin
  • If allergic/unsuitable: clarithromycin or erythromycin (if pregnant)

For bullous impetigo or impetigo in people who are systemically unwell or at high risk of complications:

  • 1st-line: oral flucloxacillin
  • If allergic/unsuitable: clarithromycin or erythromycin (if pregnant)

Children should avoid school (or adults should avoid work) until the lesions are healed, dry, and crusted over or until 48 hours after starting treatment.

Referral to secondary care

Refer to secondary care with urgency depending on clinical judgement if any of the following apply:

  • Complications arise
  • Immunocompromised and widespread infection
  • Consider in bullous impetigo, particularly babies aged 1-year-old and under
  • Frequent impetigo
  • Systemically unwell
  • At high risk of complications

Complications

In general, complications are uncommon but can include:

  • Post-streptococcal glomerulonephritis – may occur after an infection with Streptococcus species and can lead to nephritic syndrome.
  • Cellulitis, sepsis, and osteomyelitis – are more common in bullous impetigo, infants/neonates, and immunocompromised people.
  • Scarlet fever – following infection with Streptococcus pyogenes

Prognosis

  • Impetigo is usually self-limiting and clears within 2-3 weeks without treatment
  • Relapse is more likely in people with existing skin conditions (e.g. eczema)
  • Treatment with antibiotics can lead to faster resolution and a shorter infective period
  • Complications are more common and severe in neonates and immunocompromised people

Author