New research shows that one virus particle is theoretically enough to cause infection and subsequent disease.

新的研究表明，理论上，一个病毒粒子足以引起感染和继发疾病。

Bacterial endocarditis occurs when bacteria (germs) enter the bloodstream and lodge inside the heart, where they multiply and cause infection.

当细菌（微生物）进入血流和寄宿在心脏内面并在这里繁殖和引起感染时，心菌性心内膜炎发生了。

The child should try not to scratch the bumps because it may cause infection.

儿童应尽量避免划伤碰撞，因为它可能会导致感染。