An outbreak is “a sudden rise in the incidence of a disease”
An epidemic is “an outbreak of disease that spreads quickly and affects many individuals at the same time”; A pandemic is “an outbreak of a disease that occurs over a wide geographic area and affects an exceptionally high proportion of the population.”
An outbreak may become an epidemic if it spreads enough, as an epidemic may likewise become a pandemic.
[출처] www.merriam-webster.com/words-at-play/coronavirus-words-guide/covid-19