spread like wildfire idiom
（疾病或消息）迅速传播开来;（消息）不胫而走
If disease or news spreads like wildfire, it quickly affects or becomes known by more and more people.
Once one child in the school has the infection, it spreads like wildfire. 一旦学校里有一个孩子受到感染，就会迅速传播开来。