The first of these discoveries was made by a Viennese physician, Semmelwei, in 1847. It seems obvious: washing hands with soap. But, at the time, there was great controversy, and many of his peers refused to believe him. When comparing the number of women who died in childbirth at two different maternity hospitals, Semmelwei noticed that, at those where the physicians performed post-mortem examinations in the morning and deliveries in the afternoon, the mortality rate was much higher.
The solution was to order the mandatory washing of hands with soap and water before each delivery. Today, we know that this simple act - as well as other habits of personal and social hygiene, such as water and sanitation - has led to an enormous reduction in disease transmission.