Ikwueke K
Br Med J (Clin Res Ed). 1984 Nov 17;289(6455):1355-8. doi: 10.1136/bmj.289.6455.1355.
Several factors contribute towards a decrease in the prevalence of infectious disease in a population. These include active control measures, active immunisation, and improvement in the socioeconomic state of the population. There appears, however, to be a progressive increase in the resistance of a population in relation to the length of time the population has been exposed to an agent. This increasing resistance is currently thought to be an expression of natural selection but transmission of actively acquired immunity cannot be ruled out and in the light of current evidence remains a highly probable contributory factor.
有几个因素导致人群中传染病患病率下降。这些因素包括积极的控制措施、主动免疫以及人群社会经济状况的改善。然而，随着人群接触某种病原体的时间延长，人群的抵抗力似乎在逐渐增强。目前认为这种抵抗力的增强是自然选择的一种表现，但不能排除主动获得性免疫的传播，根据目前的证据，这仍然是一个极有可能的促成因素。
