After 4 hours, you can be pretty sure it has tons of bacteria, enough to make someone sick.

4个小时以后，你能十分确定它已经滋生了大量的细菌，足以致人生病。

" To infect" (infect) means to make someone sick, usually by giving them some sort of bacteria or virus.

“感染” （infect）的意思是使某人生病， 通常是给他们某种细菌或病毒。

The expression " to make (someone) sick" in this context means to become very angry, to cause very negative emotions in someone.

在这种情况下， “使（某人）生病” 一词的意思是变得非常生气， 使某人产生非常消极的情绪。