While you may not be able to catch the flu through your computer, emotions are contagious offline and online.
In 2012, Facebook infamously manipulated the news feeds of around half a million of its users. One group of these users received mainly positive posts in their feed and the second group received negative ones. The group with the more positive feed began generating more positive posts and the other group, posted more negative items.
Ideally, of course, we shouldn't be susceptible to the emotions of others - but by playing with the algorithm of their news-feed, Facebook changed the moods of hundreds of thousands of people.
Sneeze some positivity into the world of social media and hope that someone pays it forward!