If we give dates to the Irish Disaster as 1845-51, the following statement show that the basics of disease pathogens was just begining to be understood.


"John Snow was a skeptic of the then-dominant miasma theory. The germ theory of disease pioneered by Girolamo Fracastoro had not yet achieved full development or widespread currency, so Snow did not understand the mechanism by which the disease was transmitted. He first published his theory in an 1849 essay On the Mode of Communication of Cholera. Despite continuing reports, he was awarded 30,000 French francs for this work by the Institut de France. In 1855 he published a second edition of his article, documenting his more elaborate investigation of the effect of the water supply in the Soho, London epidemic of 1854.

By talking to local residents, he identified the source of the outbreak as the public water pump on Broad Street (now Broadwick Street). Although Snow's chemical and microscope examination of a water sample from the Broad Street pump did not conclusively prove its danger, his studies of the pattern of the disease were convincing enough to persuade the local council to disable the well pump by removing its handle. This action has been commonly credited as ending the outbreak, but Snow observed that the epidemic may have already been in rapid decline.

Snow later used a dot map to illustrate the cluster of cholera cases around the pump. He also used statistics to illustrate the connection between the quality of the water source and cholera cases. He showed that the Southwark and Vauxhall Waterworks Company was taking water from sewage-polluted sections of the Thames and delivering the water to homes, leading to an increased incidence of cholera. Snow's study was a major event in the history of public health and geography. It is regarded as one of the founding events of the science of epidemiology."