What Causes Vomiting and Diarrhea in Infants?

excerpted from Book of Baby and Child Care

Vomiting can be provoked either by an intestinal infection or by illness somewhere else in the body. When vomiting and diarrhea begin suddenly at the same time, the problem is usually gastroenteritis (or stomach flu), most often caused by a virus. Occasionally bacteria or even parasites are at fault.

Vomiting may also signal a problem elsewhere: an ear infection, pneumonia, urinary tract infection or even meningitis. Because of the number and variety of possible causes of persistent vomiting, a medical examination will nearly always be needed, especially in a baby less than a year of age.

Diarrhea, with few exceptions, indicates a problem focused in the bowel. Usually this is an infection most commonly viral, especially in the winter when an unsavory character known as rotavirus makes its rounds but bacteria and parasites may have to be ruled out by taking samples of stool to a local laboratory for culturing and other tests. Contaminated food can cause infectious diarrhea in older babies and children.

Antibiotics are a notorious cause of diarrhea in infants and children because they directly irritate the bowel or wipe out the normal bacteria in the intestine and allow less friendly organisms to multiply.

Food allergy, lactose intolerance or a problem with formula may also provoke loose stools, though without other signs of illness such as fever or lethargy. Some detective work with your health-care provider may be needed if your baby has persistent loose or watery stools but is otherwise doing well.