First signs of a stomach virus involve the stomach or intestines and might include loss of appetite, nausea, vomiting and/or diarrhea.

A stomach virus, or viral gastroenteritis, is a highly contagious digestive system infection. Norovirus is the leading cause in the US accounting for 19 to 21 million cases each year, according to the Centers for Disease Control and Prevention 23. Rotavirus is a less common culprit. You can contract a stomach virus by ingesting contaminated water or food, or touching a contaminated surface and getting the virus into your mouth. Since stomach viruses are so contagious, identifying early signs can help you minimize the risk of spreading the infection to others. Viral gastroenteritis usually goes away in a few days, although young children, seniors and people with a weakened immune system can be sicker for a longer period.

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.

Loss of Appetite

Loss of appetite might be the first sign that you're coming down with a stomach virus. A March 2010 review article in the journal Viruses noted that at least one study showed that norovirus infection causes a marked delay in stomach emptying -- the time it takes for food and beverages to pass from your stomach to your small intestine after eating. Researchers speculate that the delay in gastric emptying could contribute to early loss of appetite because you are unlikely to feel hungry when your stomach remains full.

Nausea, With or Without Vomiting

Delayed stomach emptying also commonly causes nausea, sometimes leading to vomiting. Children and adolescents more commonly experience vomiting with norovirus gastroenteritis than adults do, as noted in a study report published in January 2010 in the journal Clinical Microbiology and Infection 8. Eighty-four percent of adolescents aged 12 to 17 years in the study experienced vomiting, compared to 64 percent of adults aged 13 to 64, and 53 percent of seniors 65 and older. Vomiting was the first symptom of the illness in 20 percent of study participants.

Diarrhea and Abdominal Pain

Most people with a stomach virus usually experience watery diarrhea. Notably, the diarrhea characteristically does not contain mucus or blood. Mucus or blood in the stool strongly suggests another cause for your symptoms. In the Clinical Microbiology and Infection study, diarrhea was the first symptom of norovirus infection in 23 percent of participants 8. Overall, diarrhea occurred in 78 percent of adults and children studied. Among adults aged 18 to 64, 86 percent experienced diarrhea. Abdominal pain frequently accompanies digestive system symptoms, particularly among young children and adolescents. This symptom is least likely in seniors 65 and older.

Other Symptoms

While digestive system symptoms predominate when sickened by a stomach virus, you might experience other symptoms unrelated to your stomach and intestines -- although they rarely herald the illness. These symptoms might include a headache, low-grade fever, generalized achiness and lack of energy.

Dehydration is the greatest risk with viral gastroenteritis, especially among young children and seniors. Watch for signs and symptoms such as a dry mouth, decreased urination and dizziness or lightheadedness. Contact your doctor right away if any of these occur or symptoms persist for longer than 3 days. Also seek medical care right away if you or your child experience any warning signs or symptoms, including:

  • Severe or worsening abdominal pain
  • High fever
  • Vomiting blood or material that resembles coffee grounds
  • Bloody or maroon diarrhea
  • Progressive abdominal bloating
  • Extreme drowsiness or confusion
  • Fainting

If you or someone in your household has a stomach virus, be sure everyone is washing their hands with soap and water after using the bathroom or changing diapers and before eating -- and after cleaning up any vomiting accidents. Also avoid sharing food, eating utensils and drinking glasses until well after the illness has passed.