The Use of Twitter to Track Levels of Disease Activity and Public Concern in the U.S. during the Influenza A H1N1 Pandemic Signorini, Alessio ; Segre, Alberto Maria ; Polgreen, Philip M. Abstract Publication: PLoS ONE Pub Date: May 2011 DOI: 10.1371/journal.pone.0019467 Bibcode: 2011PLoSO...619467S