Modern epidemiology was born in the 1840s, delivered by John Snow, a London family doctor, an astute clinician, a polymath, a pioneer anesthetist who administered chloroform to Queen Victoria at the birth of two of her children. Beginning in the 1840s and using only rigorous logic to begin with, then, to test his hypothesis, careful observations and meticulously detailed recording of information about people's sources of drinking water, Snow worked out and published in 1855 a definitive monograph, On the Mode of Communication of Cholera[4]. This was a remarkable feat, completed 30 years before Robert Koch discovered Vibrio cholerae, the causative organism. Epidemiologists regard John Snow as our patron saint. We still use his book.