Diarrhea and fever are common symptoms of viral or bacterial stomach flu (gastroenteritis). They usually occur after the onset of generalized abdominal pain and vomiting. You may feel very ill when you have a viral stomach flu, but your symptoms will usually start to improve within 12 to 24 hours, and by 48 hours symptoms are usually mild. Home treatment is usually all that is needed. Diarrhea usually resolves in 5 to 7 days. Stools may be watery and contain very small quantities of blood or pus.

A fever of 102°F (39°C) or higher that lasts longer than 24 hours or that started 48 hours after the diarrhea began may be the symptom of a bacterial infection. Diarrhea occurs because the body is trying to rid itself of the bacteria and toxins. Symptoms that may indicate a more serious infection include shaking chills and fainting.

Fever increases your risk for dehydration by:

• Increasing fluid loss through sweating and rapid breathing to cool the body.
• Interfering with fluid replacement.