Eating bland foods such as bananas, rice, apple sauce and dry toast is sometimes easier, and these are easily digested and less likely to irritate the sensitive gastrointestinal system. There are many causes of stomach flu (gastroenteritis), including bacteria such as E coli, Shigella and Salmonella. Viruses can also cause stomach flu and are responsible for 30% to 40% of gastroenteritis cases in children. Common stomach flu viruses include norovirus or Norwalk virus, adenovirus, rotavirus, calicivirus and astrovirus. Stomach viruses are notorious for spreading rapidly because of poor hand washing. While not as common, parasites such as giardia and cryptosporidium can cause severe diarrhoea and dehydration.