> Doctors rejected hand washing for a long time because there was no theory behind why it would improve patient care

The germ theory of disease and experiments supporting the theory predate medical sanitation. (Pasteur's work did come after, but he wasn't the first.) The medical community's initial rejection of handwashing was not due to a scientifically motivated demand for a sound theory. Rather, it was due in large part to doctors' unwillingness to believe that they were the ones spreading disease from patient to patient. Additionally, the medical community at the time did not embrace the scientific method to the extent that it does today. Had it, handwashing would have been evaluated in a controlled study and proven effective.