http://arstechnica.com/science/2017/01/gunshot-wounds-are-contagious-bullets-spread-like-the-flu-study-finds/

Humans naturally comprise cohorts; groups of persons that share common circumstances, diseases, and other qualities or outcomes that we would not expect to be ‘socially transmissible’. As I have often tried to point out, the conceptual idea that ‘we are individuals, first’ is not only mistaken — it’s unlike our actual nature, humanity, potentials and experiences.