While Google has helped track flu trends for the past few years and more recently has committed to track dengue fever, a new startup called Sickweather plans to track illnesses that occur within a user’s circle of friends to help them stay well by avoiding contact with the infected. Sickweather taps into social networks like Twitter and Facebook to detect the presence of sick friends. While it’s currently in beta testing, the service expects to launch next month. The free service hopes to use an ad-supported business model to generate revenue.