2.2.2 Impetigo Contagiosa

Superficial interfollicular pyoderma.

Impetigo contagiosa has a worldwide distribution. It is found more common in infants and children, those with atopic dermatitis, and in warm, moist environments. Prevalence decreasing with adolescence. 20 cases/1000 population per year in Europe. Most cases and studies are from Asia, India and Africa. Excess of 162 million, predominantly in tropical, resource-poor contexts at one time is calculated. Pyoderma and impetigo often mixed which has led to conflicting reporting in statistics. Over a 45-year interval, the burden of impetigo has remained relatively unchanged.

Superficial cutaneous bacterial infection of the interfollicular epidermis induced almost always by Staph.aureus or Strept.pyogenes (group A beta-hemolytic).

Staphyloccal and streptococcal bacterial infection spread by fomites or direct contact, usually to predisposed skin (disturbed epidermal barrier; over-washing of children`s skin with less immunocompetence; atopic dermatitis, angular stomatitis, rhinitis, herpes simplex, pruritus with scratching). Reservoir: nose. Causative agent usually 80% staphylococci, 10% ß-hemolytic streptococci and 10% mixed infections (streptococci, less often staphylococci). In large bullous impetigo forms, one detects S.aureus strain related exfoliative toxins (exfoliating A–D), which target desmoglein 1.

First one observes macular flat, then flaccid transparent and later honey-yellowish tiny vesicular or bullous lesions. The roof of the pustule is unstable, rupture occurs and strong secretion and pus is on top of the lesion and is further disseminated by scratching. Cracked hemorrhagic-red crusts mostly in a collarette pattern are left, finally the crusts desquamate and no scars are left. In widespread cases, fever may occur. Some streptococci-induced cases start often at the lower legs as a non-bullous impetigo but develops into a crateriforme pinched-out like ulcer with necrotic crusts that persist quite longer and leave scars: those lesions are called ecthyma and are to be differentiated from necrotizing vasculitis.

In widespread streptogenic and staphylogenic types, differential blood count, CRP, urine for exclusion of glomerulonephritis. Api-Staph or Api-20-Strep test.

Neutrophilic pustule within the stratum corneum and split beneath the stratum corneum in small bullous type, in large bullous type mid epidermis with little abscesses. Sometimes a few acantholytic keratinocytes appear which may resemble Pemphigus foliaceus.

Usually self-limited, no scarring. Scratching leads to new lesions by autoinoculation. Rarely impetigo nephritis. Deep penetration of S. pygenes leads to ecthyma with scarring, more chronic course.

Dangerous: SSSS and TSS may develop. Acute glomerulonephritis when infection is caused by certain strains of streptococci.

• Dermatoses in particular eczemas with secondary impetiginization; superficial folliculitis;

• localized and widespread HSV infection (herpes simplex, eczema herpeticatum) or varicella and coxsackie virus exanthemas. In ecthyma like types, necrotizing vasculitis and Pityriasis lichenoides et varioliformis acuta.

Prevention

The first step is treating the carrier sites with application of antiseptic ointment, mostly to the nostrils. Antibacterial low acidic pH wash daily, sometimes bleach bath. Hands have to kept clean and finger nails to be cut short. In parallel, identification of source for infection and treatment.

The second step is to reduce the chance of passing the infection to another person, one should avoid close body contact. Abstain from Kindergarten or children’s playgrounds until crusts have fallen off after appropriate topical or systemic treatment. At home, the use of separate towels is recommended. Clothes have to be changed daily and to be washed at 60°C.

Therapy

First, one has to consider epidemic or endemic settings of infection.

Topical: desinfectants, dyes, ointments, wet-dry dressings if crusted.

Topical antibiotics, particularly mupirocin and fusidic acid, have become more and more resistant. This raises concerns about the long-term efficacy of topical antibiotics for impetigo. Recently, however, a new topical antibiotic ozenoxacin 1% and retapamulin show higher efficacy than muporicin.

Systemic: in widespread streptococcal types penicillinase resistant cephalosporins, erythromycin, culture-directed secondary antibiotics.