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

Abstract

Objectives Staphylococcus aureus carriage increases infection risk. We used social network analysis to evaluate whether contacts have the same S. aureus genotype indicating direct transmission, or whether contagiousness is an indirect effect of contacts sharing the same lifestyle or characteristics.

Methods The Fit Futures 1 study collected data on social contact among 1038 high school students. S. aureus carriage was determined from two nasal swab cultures and S. aureus genotype from spa-typing of a positive throat swab.

Results S. aureus carriage and spa-type were transmitted in the social network (p<0.001). The probability of carriage increased by 5.0% for each S. aureus positive friend. Male sex was associated with a 15% lower risk of transmission compared to female sex, although the prevalence of carriage was higher for men (36% versus 24%). Students with medium physical activity level, medium/high alcohol-use, or normal-weight had higher number of contacts and increased risk of transmission (p<0.002).

Conclusions We demonstrate direct social transmission of S. aureus. Lifestyle factors are associated with risk of transmission suggesting indirect social group effects on S. aureus carriage from friends having more similar environmental exposures. The male predominance in carriage is determined by sex-specific predisposing host characteristics as social transmission is less frequent than in females. Information on social network may add to a better understanding of S. aureus epidemiology.

Keywords: Staphylococcus aureus, population-based study, spa-type, network analysis