Diarrhea and vomiting Recently I experienced Diarrhoea in my four months old daughter. She started vomiting and water bowels. She was diagnosed gastroenteritis because she have been in contact with someone who has already infected or contaminated food or water. She had been miserable for two weeks or more. For adults it is not serious but for infants, older adults and people with compromised immune systems, gastroenteritis can be deadly.