drop like flies idiom informal
大批死去;成批倒下
If people are dropping like flies, they are dying or falling down in large numbers.
The heat was overwhelming and people were dropping like flies. 酷暑难当，人们纷纷病倒。
纷纷停止做（某事）
to stop doing an activity in large numbers
There used to be over 20 of us in our aerobics class but they're dropping like flies. 过去我们的有氧健身班有20多个人，但是现在很多人都退出了。