He compared annual death rates from cholera in people drinking water from
different sources and found that the risk was 14 times greater (relative risk
14) in those who drank water which was extracted from the Thames in London where
there was heavy sewage contamination. He concluded that cholera was spread from
person to person via morbid material from the alimentary canal of the sufferer
that was then swallowed by other people and had the power of multiplication in
the body of the person it attacked.