John Snow, Asiatic Cholera and the inductive-deductive method - republished

Lecture 6: Point source outbreaks

Last week, we discussed disseminated source outbreaks. In today’s post, we will discuss point source outbreaks. In a later post, we will learn about the important link between exposure and outcome.

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Snow realised that river contamination could not explain some outbreaks, which seemed to be very localised and clustered, so he added what we now call a point source outbreak to his theory.

Snow’s theory is described on the following page. Towards the end of page 56 of On the Mode of Communication of Cholera 2nd edition (MCC 2), he points out that river-borne poison is far more widely distributed (“extended”) than that from a point source outbreak, i.e. originating from a single point such as a well or a pump.

Whatever the means of transmission, however, Snow repeatedly pointed out the close connection betwee…