Impetigo is a superficial, contagious, blistering infection of the skin caused by the bacteria Staphylococcus aureus and Streptococcus pyogenes

Spread is by direct contact with discharges from the scabs of an infected person. The bacteria invade the skin through minor abrasions and then spread to other sites by scratching. Infection is spread mainly by the hands, but indirect spread via toys, clothing, equipment and the environment may occur.

The incubation period is between 4 to 10 days.

It has two forms:

• non-bullous
  • Non-bullous impetigo is the more common form (70% of cases), in this form vesicles (fluid filled lesions <0.5cm in diameter) may appear transiently early in the disease.
  • Lesions occur at sites of skin trauma
  • due to staphylococcus or streptococcus
• bullous (Bullae are fluid-filled lesions of >0.5 cm in diameter)
  • due to staphylococcous aeurus
  • Lesions occur on intact skin

Bullae/vesicles rupture to form yellow crusted lesions

Risk factors:

• Increased humidity - increase risk of microtrauma
• Poor hygiene, malnutrition, overcrowding - Increased skin colonisation
• Comcomitant skin disease - scabies, pediculosis capitis (head lice), atopic eczema - result in early destruction of epidermal barriers

PC

Non-bullous

• Small vesicles (fluid-filled cyst < 5 mm) or pustules develop at the site of infection and then rupture leading to the release of exudate that crusts over with a classic golden/brown colour.
• Sites: face, limbs, flexures

Bullous

• characterised by the development of large bullae (fluid-filled cysts > 5 mm) that may increase to 2 cm in size and then rupture leaving a thin yellow/brown crust.