First, you should tell your coworkers, but you have to say not wear emotions.
You should advise him that if he was sick, flu or cough it is cloth gagged or not, medication 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.