Description Throughout history, more people have died in disease epidemics than in wars or other disasters. The courageous, trail-blazing defenders against these diseases faced a terrifying personal gamble. Often they were ignored, laughed at, or even fired from their jobs. But they kept hunting for answers, putting the pieces of the epidemic puzzle together. ..As they looked for clues to the origin of a disease, scientists searched for the unknown "patient zero" -- the first person to have contracted it. In nineteenth-century London, Dr. John Snow's mapping of an epidemic found that patient zero was a six-month-old baby, whose cholera-laden diarrhea had contaminated the water of a local pump. It led to the death of 10,000 inhabitants exposed to the dirty water. .