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

Lecture 4: Competing theories on the origin and spread of infectious disease

Last week, we discussed what was known about the spread of Asiatic Cholera, Snow’s observation of the incubation period, and the problems with defining numerators and denominators. In today’s post, we will describe the competing theories on the origin and spread of infectious diseases that existed in Snow’s time. In the next post, we will learn about disseminated source outbreaks.

The Snow series is an educational course. We hope you will recognise our efforts by donating to TTE or becoming a paying subscriber, as writing the series took a lot of time and effort.

There were two main competing theories as to the origin and communication of cholera and other diseases:

Miasma Theory (Anticontagionism)

Many in the early to mid-nineteenth century felt that cholera was caused by bad air arising from decayed organic matter or miasmata.  "Miasma" was believed to pass from cases to susceptibles in diseases considered contagious. Believers in the miasma theory stressed the eradication of disease …