Impetigo: Aetiology

Impetigo is caused by Staphylococcus aureus (usual causative agent of the bullous type), Group A beta-haemolytic Streptococcus pyogenes (usual causative agent of the non-bullous type), or both. Minor abrasions and skin lesions, associated with a wide variety of skin diseases, allow bacterial introduction into the skin. These bacteria colonise and then infiltrate the superficial layers of the skin, initially creating a small erythematous macule (a flat, discoloured area of skin), which soon becomes vesicular. MRSA can be a causative organism and is seen more often in cases of non-bullous impetigo.

Clinical classification

Bullous impetigo: bullae are fluid-filled lesions >0.5 cm in diameter.

Non-bullous impetigo: impetigo without bullae.