If you’ve come down with a bug, you may wonder how long someone with the stomach flu is contagious. First, you need to look at which type of virus you have. Most adults have norovirus. You will begin to get sick within 2-3 days of exposure. You will be contagious from the moment you begin to feel ill. You will continue to be contagious for at least three days after you are better, but it may take longer. Children typically get rotavirus and are contagious for much longer than adults. They are contagious several days prior to coming down with symptoms and are contagious for 2 weeks after their last symptom is gone. To prevent passing on germs, good hand washing habits are essential.