What was John Snow's contribution to public health during the cholera epidemics?

John Snow's contribution to public health during the cholera epidemics is primarily recognized for identifying the source of outbreaks, specifically through his investigation during the 1854 Broad Street cholera outbreak in London. Snow famously mapped cases of cholera and noticed a clustering of cases around a particular public water pump on Broad Street. His meticulous data gathering and analysis led him to hypothesize that contaminated water, rather than miasma or "bad air," was the cause of cholera transmission.

This groundbreaking work laid the foundation for modern epidemiology and demonstrated the importance of clean water and sanitation in controlling disease outbreaks. By pinpointing the water source, Snow not only helped to resolve that specific outbreak but also shifted public health policies toward improving urban sanitation and understanding disease spread through environmental factors. His approach exemplified the use of data in epidemiology and the need for public health interventions based on scientific evidence.