take a turn for the worse 恶化；情况转坏；病情恶化；逆转

【例句】
Even following the best medical care, patient health can take a turn for the worse after returning home.
即使接受了最好的医疗护理，病人回家后其健康状况也可能会恶化。

However, in time business may take a turn for the worse.
然而，生意迟早会急转直下。