epidemic是地方流行病。看到这个pandemic的解释，非常好：

What are pandemics?

A pandemic is a global disease outbreak. It differs from an outbreak or epidemic because it:

• affects a wider geographical area, often worldwide.
• infects a greater number of people than an epidemic.
• is often caused by a new virus or a strain of virus that has not circulated among people for a long time. Humans usually have little to no immunity against it. The virus spreads quickly from person-to-person worldwide.
• causes much higher numbers of deaths than epidemics.
• often creates social disruption, economic loss, and general hardship.

https://apic.org/monthly_alerts/outbreaks-epidemics-and-pandemics-what-you-need-to-know/