Patterns and Predictors of Staphylococcus aureus Carriage during the First Year of Life: a Longitudinal Study.

We sought here to investigate the patterns of Staphylococcus aureus carriage in the first year of life, its determinants, and the dynamics of transmission between mothers and infants. A prospective longitudinal cohort study of S. aureus carriage among mothers and their infants was performed, including monthly screenings from pregnancy/birth through the first year of the infant's life. Medical and lifestyle data were collected. Infant S. aureus carriage was detected from rectal and nasal swabs, and maternal carriage was detected from nasal and vaginal swabs. Multivariate analysis and a nonlinear mixed model (NLMIXED) were used to determine the predictors of carriage and S. aureus persistence. Of the 671 women recruited, 130 women carried S. aureus at recruitment (19.3%); they and their 132 infants were included in the study. A total of 93% of the infants acquired S. aureus sometime during the first year of life; 64% of these infants acquired the maternal strain, mostly (66%) during the first month of life. We observed that 70 women (52.50%) and 17 infants (14%) carried S. aureus persistently. Early acquisition of S. aureus carriage was associated with longer duration of initial carriage and was the most significant predictor of S. aureus persistence, while day care center attendance was negatively associated with persistent carriage. Methicillin-resistant S. aureus was carried by two infants for only 1 month each and not by any of the mothers. Early acquisition of S. aureus, mostly from the mother, is thus an important determinant of carriage persistence in infancy.