IS EBOLA HERE TO STAY? Why scientists continue to be perplexed by how to define the outbreak that has killed 7,000. “The flu, for example, is endemic in the U.S. because various strains reappear the following year without any trouble. Yet the many Ebola outbreaks of the past 40 years are not referred to as endemic because the original source of the infection in each case is widely believed to be an animal that somehow infected a human. Changing the technical description of the current outbreak from epidemic to endemic is more than a matter of semantics. The difference between responding to an epidemic versus an endemic disease is as great as the difference between preparing for a sprint versus a marathon.”