Germ theory Before 1847 doctors didn't have to wash their hands before an operation. lgnaz Semmelweis, a doctor from Vienna, realised that women in labour could be dying from infactions passed on by the hands of their doctor. this became the germ theory of disease. At the end of the 19th century,infaction caused 30% of deaths. By the end of the 20th century it caussed less than 4%