“Contagious” is an interesting word, especially when used outside the world of health care, carrying both positive and negative connotations, such as, “her laughter was contagious” or “a financial contagion has hit the markets.”
Of course, within health care “contagious” almost always has negative connotations – “that strain of flu is rather contagious” or “ebola hemorrhagic fever is highly contagious and kills approximately 50 to 90 percent of all people infected." There was even a recent study published by NEJM showing that obesity within social networks is contagious. The social network map that accompanied the study is literally covered with dozens of interconnected, rather plump yellow dots. The skinny dots wedged in-between were apparently feeling a lot of social pressure to eat a second or third doughnut!
Nicholas Christakis and James Fowler who conducted the obesity research noted that “we find that a person’s chances of becoming obese increase by 57% if they have a friend who becomes obese, 40% if they have a sibling who becomes obese, and 37% if a spouse becomes obese.”
Unfortunately, their related research showing healthy behaviors within social networks are also contagious has received much less media attention. In analyzing the Framingham cohort for smoking cessation, they noticed some remarkable trends:
…there appear to have been local smoking-cessation cascades, since whole connected clusters within the social network stopped smoking roughly in concert. This finding suggests that decisions to quit smoking are not made solely by isolated persons, but rather they reflect choices made by groups of people connected to each other both directly and indirectly at up to three degrees of separation. People appeared to act under collective pressures within niches in the network.
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