Excerpt from Staphylococcal Scalded Skin Syndrome

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Background

Staphylococcal scalded skin syndrome (SSSS) is a toxin-mediated type of exfoliative dermatitis. Toxin-mediated staphylococcal syndromes comprise a group of blistering skin diseases, ranging in severity from localized bullous impetigo to SSSS, in which superficial blistering and exfoliation follow widespread painful erythema.

Pathophysiology

The disorder is caused by toxigenic strains of Staphylococcus aureus, usually belonging to phage group 2 (types 3A, 3B, 3C, 55, or 71). Two exotoxins (ETs), epidermolytic toxin A (ET-A) and epidermolytic toxin B (ET-B), are responsible for the pathologic changes seen in SSSS. These toxins cause intraepidermal splitting through the granular layer by specific cleavage of desmoglein 1 (also the target protein in the autoimmune blistering dermatosis, pemphigus foliaceus), a desmosomal cadherin protein that mediates cell-to-cell adhesion of keratinocytes in the granular layer.

Specific targeting of desmoglein 1 by ETs allows S aureus to proliferate and spread beneath the barrier of the skin. Crystal structures and amino acid sequences indicate that these toxins act as serine proteases and cleave desmoglein 1 after glutamic acid residue 381 between extracellular domains 3 and 4. The ET-A and ET-B amino acid sequences are approximately 40% identical with each other.

Recently, researchers have found an additional ET family member, ET-D, by screening the genomes of S aureus isolated from patients with skin infections. They demonstrated that ET-D specifically digested desmoglein 1. However, only ET-A and ET-B have been firmly linked to human SSSS. The ET-D gene was detected mainly in isolates from patients with skin and soft-tissue infections, such as furuncles, abscesses and finger pulp infections.

It has been suggested that ET-B is more frequently isolated than ET-A in children with SSSS. This link between ET-B and generalized SSSS might be due to increased virulence of ET-B or to more abundant ET-B release. Because ET-A is chromosome borne and ET-B is plasmid borne, multiple copies of the ET-B gene could possibly lead to higher ET-B production. However, levels of ET-A and ET-B are quite similar in vitro. The link between ET-B and generalized SSSS may be explained, at least in part, by lower levels of anti-ETB antibodies than anti-ETA antibodies in the general population.

An asymptomatic adult carrier introduces the causative bacteria into the nursery. Asymptomatic nasal carriage of S aureus occurs in 20-40% of healthy individuals, with the organism being isolated from the hands, the perineum, and the axillae in a smaller proportion of the general population.

Frequency

United States

SSSS most commonly occurs in infants and in young children, and it tends to occur in outbreaks in neonatal nurseries or in day care nurseries. Large outbreaks of SSSS in neonatal nurseries have been described, but the occurrence of SSSS in adults as a nosocomial infection appears to be exceptional; epidemics have never been observed.

Epidemiologic data on strains of S aureus that produce ET are scarce. In a prospective clinical and bacteriologic study, 5.1% of 944 isolates of S aureus were identified as ET producers. SSSS in adults is an exceedingly rare disorder, with only 50 reported cases.

Mortality/Morbidity

Children generally do well and are not as ill as their dramatic eruptions might suggest. SSSS is usually associated with a trivial infective focus in the conjunctivae or the skin; however, severe infections, such as sepsis, do contribute to a low but appreciable fatality rate (4%).

• Morbidity in the occasional child who develops cellulitis, sepsis, and pneumonia can be significant.
• In children, the foci of staphylococcal infections are usually the nasopharynx or localized skin infections.
• Adults with SSSS often have blood cultures positive for toxigenic S aureus, and mortality rates can be high (>60%). In older patients, risk factors consisting of immunosuppression in tumor patients and underlying consumptive infectious diseases contribute to high mortality.

Race

Black children are less prone to SSSS than white children.

Sex

A male-to-female predominance exists (2:1 in sporadic cases, 4:1 in epidemics).

Age

• The disease most commonly affects children younger than 5 years, particularly neonates. A decreased ability to achieve renal clearance of toxins and a lack of specific immunity (antibody) to the toxins make neonates the group at highest risk.
• Older children and adults may also develop the disease. In such cases, renal insufficiency or immunodeficiency (eg, HIV infection, advanced stage of cancer) appears to explain the susceptibility to the syndrome. This happens because for the development of SSSS, a massive production of toxins or deficiency in their elimination must be present. Adults who are affected range in age from 19-91 years, with one half of the cases occurring in adults older than 60 years.

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