Twitter and public health.

Twitter can serve as a powerful communication modality to both "push" and "pull" public health data; each user is a potential public health sensor and actor. However, in 2012, only 8% of local health departments had Twitter accounts. We outline how Twitter works, describe how to access public tweets for public health surveillance purposes, review the literature on Twitter's current and potential role supporting public health's essential services, summarize Twitter's limitations, and make recommendations for health department use.