We also see that clusters of people co-occur with clusters of strains, suggesting the existence of social network niches wherein similar individuals share similar microbes.

After two years, we studied the microbiome of 301 individuals and found that socially connected people had become more microbially similar than those who were not connected

Your microbiome can predict who your friends are, better than shared sociodemographic characteristics. Additionally, we have evidence of transmission chains; your friend’s friend is sharing some strains with you as well.

Using strain-level analyses, we show that strain transmission occurs in different relationship types, even between people not living in the same household and friends. We saw more transmission between people who interacted with each compared to those who had no relationship at all.