The stomach “bug” is usually a sickness caused by a virus which spreads from person to person or through food contamination. Symptoms usually appear 1 to 2 days after exposure. Symptoms are often mild and usually only last a day or two.You may experience some of the following symptoms: 1  Upset Stomach.2  Diarrhea. 3  Vomiting. 4  Fever.he stomach “bug” is usually a sickness caused by a virus which spreads from person to person or through food contamination. Symptoms usually appear 1 to 2 days after exposure. Symptoms are often mild and usually only last a day or two. You may experience some of the following symptoms: