Prevalence and molecular characteristics of Staphylococcus aureus isolates colonizing patients with atopic dermatitis and their close contacts in Singapore

Staphylococcus aureus colonization is an established pathogenic factor for disease flare in atopic dermatitis (AD). We conducted a study to investigate the colonization of S. aureus in patients with AD and their close contacts in order to evaluate the possibility of intrafamilial transmission. We sought to determine the distribution of the bacterial virulence factors and their correlation with disease severity. Nasal swabs and skin swabs (patients with AD only) were taken from patients with AD aged 2-21 years and their close contacts, seen at the National Skin Centre from January to March 2007. All S. aureus isolates were typed using multilocus variable-number tandem-repeat fingerprinting (MLVF) and screened for virulence factors via polymerase chain reaction (PCR) analysis. AD severity was determined by the SCORAD index. A total of 34 patients with AD and 55 close contacts were recruited. Thirty-one (91%) patients were colonized with S. aureus. Twenty-five (45%) of their close contacts were also colonized, and MLVF showed a high concordance of S. aureus isolates in index patients and their close contacts. On multivariate analysis, patients with a moderate SCORAD were more likely to be colonized by enterotoxin B-positive S. aureus (P = 0.027). No virulence factor was significantly associated with a severe SCORAD. The prevalence of S. aureus colonization was high among patients with AD and their close contacts. However, no predominant isolate of S. aureus was found to be associated with AD. The presence of superantigen B is possibly associated with moderate rather than severe disease in our population.