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Social network analysis of Staphylococcus aureus carriage in a general youth population

Staphylococcus aureus nasal carriage increases risk of infection and has been associated with lifestyle behavior and biological host characteristics. We used social network analysis to evaluate whether contacts have the same S. aureus genotype, or whether contagiousness is an indirect effect of contacts sharing the same lifestyle or characteristics. The Fit Futures 1 study collected data on social contact among 1038 first level students in the same high school district in Norway. S. aureus persistent carriage was determined from two nasal swab cultures and genotype from spa-typing of a positive throat swab culture. Bootstrap, t-tests, logistic regression, and autocorrelation were used to evaluate social network influence on host risk factors and S. aureus carriage. Both persistent carriage and spa-type were transmitted in the social network (p<0.001). The probability of carriage increased by 3.7% and 5.0% for each additional S. aureus positive friend, in univariable regression and multivariable autocorrelation analysis respectively. Male sex was associated with a 15% lower risk of transmission compared to women, although the prevalence of carriage was higher for men (36% versus 24%). Medium physical activity, medium and high alcohol-use, and normal-weight students had higher number of contacts, and increased risk of transmission (p<0.002). We demonstrate direct social transmission of S. aureus in a general youth population. Lifestyle factors are associated with risk of transmission suggesting indirect social group effects from having more similar environmental exposures. The predominance in carriage is determined by sex-specific predisposing host characteristics as social transmission is less frequent than in females. Better understanding of how social interactions influence S. aureus carriage dynamics in the population is important for developing new preventive measures.