First, you should tell your coworkers, but you have to say not wearing emotions.
You should advise him that if he was sick, flu or cough you should use mask or notmedication and sleep at home.
And you're the boss, you can listen to explained that due to the fact that people have a cold one, and then touch it to spread the germs that are different. We want to catch us, it makes the disease, flu infections.