Caused by Staphylococcus aureus, Group A streptococcus or both. 2 forms, bullous and nonbullous (or crusted). Bullous impetigo is always due to staphylococci. Blisters increase rapidly in size and number, rupturing to produce erosions with a peripheral brown crust. May clear centrally to produce annular lesions. Neither itchy nor painful.
Nonbullous impetigo begins with a small transient vesicle on an erythematous base which leaks to produce a thick soft yellow crust. The lesions remain much smaller than those of bullous impetigo.
Impetigo is often superimposed on other skin diseases such as insect bites, scabies, pediculosis and atopic eczema. As impetigo is an intraepidermal infection, the condition does not scar although postinflammatory pigmentation can occur, particularly in dark-skinned patients.
Impetigo is very infectious. Saline bathing may be used to dry out the lesions and a swab for culture and sensitivity testing should always be taken. Topical mupirocin may be used in the well patient with localized disease. Because of the rarity in most areas of pure streptococcal impetigo, flucloxacillin or erythromycin are the treatments of choice while awaiting culture results. In many areas of the world there is an emergence of erythromycin-resistant staphylococci. Associated with rheumatic fever and glomerulonephritis in the developing world.