Symptoms

Although it's commonly called stomach flu, gastroenteritis isn't the same as influenza. Real flu (influenza) affects only your respiratory system — your nose, throat and lungs. Gastroenteritis, on the other hand, attacks your intestines, causing signs and symptoms, such as:

• Watery, usually nonbloody diarrhea — bloody diarrhea usually means you have a different, more severe infection
• Abdominal cramps and pain
• Nausea, vomiting or both
• Occasional muscle aches or headache
• Low-grade fever

Depending on the cause, viral gastroenteritis symptoms may appear within one to three days after you're infected and can range from mild to severe. Symptoms usually last just a day or two, but occasionally they may persist as long as 10 days.

Because the symptoms are similar, it's easy to confuse viral diarrhea with diarrhea caused by bacteria, such as Clostridium difficile, salmonella and E. coli, or parasites, such as giardia.

When to see a doctor

If you're an adult, call your doctor if:

• You're not able to keep liquids down for 24 hours
• You've been vomiting for more than two days
• You're vomiting blood
• You're dehydrated — signs of dehydration include excessive thirst, dry mouth, deep yellow urine or little or no urine, and severe weakness, dizziness or lightheadedness
• You notice blood in your bowel movements
• You have a fever above 104 F (40 C)

For infants and children

See your doctor right away if your child:

• Has a fever of 102 F (38.9 C) or higher
• Seems lethargic or very irritable
• Is in a lot of discomfort or pain
• Has bloody diarrhea
• Seems dehydrated — watch for signs of dehydration in sick infants and children by comparing how much they drink and urinate with how much is normal for them

If you have an infant, remember that while spitting up may be an everyday occurrence for your baby, vomiting is not. Babies vomit for a variety of reasons, many of which may require medical attention.

Call your baby's doctor right away if your baby:

• Has vomiting that lasts more than several hours
• Hasn't had a wet diaper in six hours
• Has bloody stools or severe diarrhea
• Has a sunken soft spot (fontanel)on the top of his or her head
• Has a dry mouth or cries without tears
• Is unusually sleepy, drowsy or unresponsive