单词 endemic、epidemic 及 pandemic 往往会造成混淆，我想在此说明这些单词在应用于公共卫生领域时的差异。
Endemic 主要当作形容词使用（当作名词使用时，这个单词是 endemic disease 的简化形式）。当作形容词使用时，endemic 表示“特定时间、地点或群体所特有的”。因此，endemic disease 指影响范围相当有限的疾病。此外，endemic disease 并不包括“短暂流行”的意思，所以应该将其解释为长期或永久性的现象。与此相反，epidemic 指短暂爆发的疾病，患者人数突然显著增加、疾病迅速扩散，之后又突然销声匿迹。所谓的 epidemic，并不局限于特定群体或地区，也不限定为长期性质。Pandemic 的意思与 epidemic 非常相近，唯一的差别在于两者的规模。通常，pandemic 指影响范围达到全国或全球规模的传染病爆发。
以下例句说明这三个名词及其形容词的正确用法。
- In order for an infectious disease to be endemic to a region, each infected person must, on average, infect one other person; if the transmission rate is lower, the disease will die out, while if it is higher, the infection rate will increase exponentially, and the disease will become epidemic.
- An epidemic will eventually disappear or leave an endemic disease. In either case, however, there is the chance that an epidemic may reappear in the future.
- The first influenza pandemic of the 21st century was the “swine flu” (Influenza A/H1N1) outbreak of 2009–2010. It was first reported in Mexico and eventually spread throughout the world, killing over 6,000 people.
[1] 这些单词也可应用于其它上下文，不过就 pandemic 而言，这种用法比较罕见。
