I can see the correlation in adoption rate, but social media users don't get purged from networks like infectious diseases do from our bodies.

The reasons people use and/or leave social networks are completely different from the reasons diseases leave the body, which is the correlation needed for this study to make sense. It just seems like linkbait to me.

Interesting corollary: if you've got two smaller social networks, both trying to grow, of equal sizes, the one with a denser group bond (more edges between nodes) has a better shot at it than the sparser one.

Which is to say: start with a tight group and you'll tend to grow -- the benefits to members of participating (and costs of defecting) are higher. With a widely distributed network, not so much.

Facebook exploited this with its initial seeding: Harvard / Ivys / selective colleges / all edus / general public.

If I recall, a strong reason for Orkut's failure to launch was that it never really developed a tight inside bonded group outside of Brazil and Latin America.

Much as epidemics spread in densely populated areas.

Gives a new meaning to "viral media" and "social disease".