diarrhea vs diarrhoea

diarrhea

noun
  • A gastrointestinal disorder characterized by frequent and very soft or watery bowel movements. 

  • The watery or very soft excrement that comes from such bowel movements. 

diarrhoea

noun
  • British standard spelling of diarrhea. 

How often have the words diarrhea and diarrhoea occurred in a corpus of books? (source: Google Ngram Viewer )