The association between S. aureus colonization on cheek skin at 2 months and subsequent atopic dermatitis in a prospective birth cohort

S. aureus may worsen already established atopic dermatitis (AD), but its primary role in the etiopathogenesis of AD and possible severity is unclear. To compare the prevalence of S. aureus colonization in early infancy in children that developed AD during the first 2 years of life with children that did not. In this prospective birth cohort study including 450 infants, we analyzed bacterial swabs collected from cheek skin at 0 and 2 months of age. The development of AD, and its severity, was monitored prospectively for 2 years and diagnosed by a physician. Information on parental atopy, filaggrin gene mutation status, and use of antibiotics and emollients was accounted for in the analyses. At birth, occurrence of S. aureus colonization was similar in infants with and without subsequent AD. At 2 months of age, S. aureus colonization was more common in children that later developed AD (adjusted Hazard Ratio 1.97 [confidence interval 1.21; 3.19], p=0.006). No association was found between S. aureus colonization and AD severity or age at onset. It remains unknown whether colonization with S. aureus may directly increase the risk of AD, or whether it is a secondary to skin barrier impairment or a skewed immune activity, but according to our findings, colonization is more commonly increased at 2 months of age in children that later developed AD.