You know, people with colds or the flu or something. The startup is called Sickweather and it will mine data from Twitter, Facebook and people who sign up for the service as users.
"Sickweather's founders hope the data they collect can help users avoid catching their friends' bugs. Users would be able to log in to the site and view a map showing illnesses in their area. They would also see updates from friend connections mentioning current illnesses. The company plans to release mobile apps for the site as well, so that users can view this information while on the go."
How would it work? Just look for words that have to do with being sick. Again, from MIT's Technology Review: Michael Belt, Sickweather's chief technology officer, says the company searches for keywords related to sickness. To tune the algorithm, the system uses a database of words that exclude certain posts. For example, the system would want to record a post that says, "I'm feeling so sick--my nose is running." But it would exclude a post that says, "There were some sick beats last night at the club."