It's not just in the stomach, and it's not a flu.
Officially called viral gastroenteritis, a stomach virus also causes inflammation and irritation in the small intestine and has nothing to do with the respiratory virus we call influenza. Influenza is spread through the air when a sick person coughs or sneezes; your child picks up a stomach virus when he touches a surface or an object or eats a food that's contaminated with infected stool or vomit. Symptoms include nausea, vomiting, diarrhea, stomach cramping, fever, and body aches. Diarrhea can last for several days; most of the other symptoms subside within 48 hours.