#Ebola: Emergency Risk Messages on Social Media.

Public health threats require effective communication. Evaluating effectiveness during a situation that requires emergency risk communication is difficult, however, because these events require an immediate response and collecting data may be secondary to more immediate needs. In this article, we draw on research analyzing the effectiveness of social media messages during times of imminent threat and research analyzing the emergency risk communication conceptual model in order to propose a method for evaluating emergency risk communication on social media. We demonstrate this method by evaluating 2,915 messages sent by local, state, and federal public health officials during the 2014 Ebola outbreak in the United States. The results provide empirical support for emergency risk communication and identify message strategies that have the potential to increase exposure to official communication on social media during future public health threats.