It is well known that the Internet can be useful in monitoring disease outbreaks as different approaches have shown in recent studies, for instance based on the use of search engines (e.g. Google Trends) and Web 2.0 channels such as blogs, Facebook and Twitter.
I would like to focus on the use of Twitter in this fashion. Recently, Paul MJ et al. have published a paper ("You are What You Tweet: Analyzing Twitter for Public Health") where the messages of social media users are analysed in order to find out information to be useful for Public Health. The idea is to aggregate millions of messages to generate relevant knowledge, in that case, trying to get diverse public health measures, taking into account that Twitter (and social networks in general) may be a new Internet-surveillance method characterized by an important message volume, frequency and public availability. One of the problems I see is the fact that these messages and people behind them may represent a certain reality that could not be applied to the majority of cases or scenarios in terms of Public Health (probably many unknown factors play role in this environment). Nevertheless, I'm sure it's a very interesting line of research that needs to be more studied in depth.