Question about Diarrhea...?

My husband is complaning this couple of weeks that he fells weaknes (because he is working like 12 hours a day, and he bearly eats something, while he is at workd)! These couple of days he has diarrhea and he doesn't have apitet! The doctor said that he would have to take blood exm. and exmp. from the stool, because he is suspecting some virus infection! I am all in worries, can somebody tell me what can it be??? THank you p.s. sorry for the mistakes..