As a former state epidemiologist, I will say that epidemics are — complex. The first complexity is that the definition of an epidemic typically references a “widespread” occurrence of a disease without a common definition of what “widespread” means. A single case of Ebola or Measles in an area that has not had any cases before would be considered an outbreak and more than a few cases in a region might be considered an epidemic. Whereas, in a typical season, a single case of the flu would not be considered an outbreak and a few cases in a region would not be considered an epidemic. Unlike the flu, where there is a defined “epidemic threshold” that can be modeled from years of data, for many recent high-profile outbreaks, no such formal experience or data exists to allow that kind of formal definition and determination. We rely on local, national and global public health organizations and leaders to formally declare an “epidemic” or a “pandemic”, but these determinations have a relative nature to them in many cases.