Clarifying the transmission route of Staphylococcus aureus colonizing the skin in early childhood atopic dermatitis

Background: We previously found that skin-colonizing Staphylococcus aureus in early childhood atopic dermatitis (AD) originates predominantly from the patient's nose, whereas maternal transmission did not contribute substantially to colonization. Objective: To investigate the transmission route and definitive source of skin-colonizing S aureus in early childhood AD. Methods: A total of 527 children and 32 healthy teachers from 2 kindergartens and 1 elementary school were included in the study. Children were screened for AD and categorized into 3 groups (AD, borderline, and healthy). Samples were collected from 5 to 6 different body sites, including the skin, subungual spaces, and anterior nares. The identity of colonies apparent on mannitol salt agar plates was confirmed by polymerase chain reaction amplification of the nuc gene. The genotypic composition of cultured isolates was examined by pulsed-field gel electrophoresis and analyzed with a dendrogram. Results: The total colonization rate was higher in the AD group (34.6%) than in the borderline (21.1%) and healthy groups (25.4%). In the AD group, S aureus was more frequently cultured from the subungual areas (30.8%) than the anterior nares (19.2%). To assess self-contamination or recolonization, dendrogram analysis revealed that most isolate pairs (22/23) had the same pulsed-field gel electrophoresis pattern. Conclusion: As with the anterior nares, the subungual spaces are important reservoir of skin-colonizing S aureus in early childhood AD. The transmission route for self-contamination or recolonization of S aureus appears to be from children's anterior nares to the skin through their own fingers. Child-to-child and/or teacher-to-child transmission in a classroom do not seem to be definite routes of S aureus transmission.