An example is blood transfusion; in recent years, to reduce the risk of transmissible infection in the blood supply, donors with only a small probability of infection have been excluded.
这样的一个例子就是输血；近年来，为了在血液供应过程中减少传播传染性疾病的风险，那些感染概率即使很小的献血者也已被排除在外。