What is gastroenteritis? Gastroenteritis (gastro) is a bowel infection that causes diarrhoea (runny, watery poo) and sometimes vomiting. The vomiting may settle quickly, but the diarrhoea can last up to 10 days. Gastro can be caused by many different germs, although the most common cause of gastro is a viral infection. Gastroenteritis, also known as ‘gastro’, is a common illness that can cause vomiting and diarrhoea. Many types of gastro are easily spread. Gastro is not usually serious but it can make you very dehydrated. Milder forms can be managed at home by drinking fluids. Gastroenteritis Causes, gastroenteritis symptoms