Your child might not have a virus at all.
Doctors can't always distinguish between a stomach virus and food poisoning -- or even appendicitis. That's because all three conditions can cause pain and vomiting. However, fever generally doesn't accompany food poisoning, and diarrhea is not often associated with appendicitis. (ER docs frequently miss appendicitis in young children, but the telltale clue is sharp pain that starts around the belly button and moves to the lower-right side of the abdomen.) Food poisoning usually comes on suddenly and is gone within 12 hours, says Charlotte Cowan, MD, author of the children's book The Moose with Loose Poops.