What's normal: One or two cases a year is average; up to three episodes is within the normal range.
What's not: Diarrhea that lasts more than five days; dehydration.
Why your child may be vulnerable: The loose bowels of babyhood and early toddlerhood can be impressive both in their number and explosive power. Most are caused by the highly contagious rotavirus. This feisty misery-spreader can live for up to seven hours on a countertop and survive for nearly half an hour on your hands if you touch an infected surface. A smidgen of diarrhea contains 100 billion rotavirus particles, while it takes just 10 to pass the infection along. So imagine the yucky probabilities.
It's all too easy for rotavirus to be passed around in your own home, and far easier at daycare. (Fortunately, washing hands with soap deactivates the virus.)
But don't blame all loose bowels on viral invaders. "Some antibiotics, such as Augmentin, Biaxin, and Zithromax, can speed up transit time in the bowels," Dr. Fisher notes. "And for young toddlers, the most common cause of frequent diarrhea is diet. Too much fruit juice makes the bowels pull in extra water." Other dietary causes include lactose or soy intolerance.
Advice for parents: Limit fruit juice, since it has little nutritional value, says Dr. Fisher. Also, go easy on milk; if your child has had a bout of diarrhea, her gastrointestinal system may be hypersensitive for a while.