The Flu

Just wondering about the flu. My hubby has had it for 4 days, the first day vomitting then just alot of caughing achy, conjestion, lightheaded, etc. He tried to go to work this morning and had to leave 1 hr in, because he felt dizzy , caughing and so on. Just wondering how long is he contagous for? Are you only contagous when you are developing the flu and not when the symptoms appear?
Thanks, Carm :)