Between 1848 and 1854, a series of cholera outbreaks occurred in Broad Street, Golden Square, in Soho, and other impoverished regions of central London with poor hygiene and housing, resulting in large-scale loss of life1. The mechanism of cholera transmission was unclear. During that time, people believed that diseases like cholera, dysentery, or plague were caused by "bad air" or foul smell (miasma theory)2. The unknown cause of cholera was major public health challenge as interventions based on miasma theory were ineffective. Dr. John Snow, physician and anesthetist practicing anesthesia in cholera endemic areas, challenged the miasma theory and hypothesized that cholera was transmitted through contaminated water.
To test his hypothesis, Dr. Snow systematically observed,
collected, and analyzed data. He examined death records, checked cholera
clustering patterns by demographic characteristics, plotted cases on a map, and
performed comparative analyses. In a cholera epidemic (August-September 1854) in
Soho, he observed approximately 600 deaths within a 10-day period among those
who lived near or consumed water from the Broad Street pump. He also identified
that brewery workers and residents relying on local wells escaped the epidemic2,3. Dr. Snow investigated another epidemic (September-October
1854), which occurred in Newington and a part of Camberwell with overlapping
water supply from Lambeth Company (LC) and Southwark and Vauxhall company (SVC).
Both companies supplied water to households across different socio-economic groups,
allowing the meaningful comparison between households with similar
characteristics. He compared cholera-related death rates between households by place
of residence and water supplying company1.
By mapping and comparing cholera-related deaths among people
drinking water from Broad Street pump vs local wells, he found that mortality
rate was higher in the households using water from the pump compared to local
wells. On investigation of subsequent outbreak, he found that the LC moved its
water intake upstream to cleaner part of Thames River, while the SVC continued
drawing water from the sewage-polluted section. The cholera-related mortality
rate was higher in households supplied by SVC compared to households supplied
by LC and in the rest of London, with 14 times higher fatalities than LC1.
Findings from his investigation in both the outbreaks concluded
that contaminated water was the source of cholera epidemic rather than bad air.
With this evidence, he persuaded civic authorities to remove pump’s handle which
helped epidemic subside in a few days. His works eventually helped to design and
implement effective interventions, such as chlorination and water filtration, to
promote safe drinking water and prevent water-borne disease epidemics.
Dr. Snow’s pioneering use of mapping, population
comparisons, and observational analysis established methodological standards
for identifying environmental sources of disease and assessing causation in
public health research. His investigations contributed to establishing the
validity of the Germ Theory, which was highly controversial at this time. His
use of mapping effectively linked public health with spatial analysis for the
first time in history, serving as a precursor to modern Geographic Information System
applications in epidemiology. His work also demonstrated that effective public
health interventions could be implemented without knowing the exact causative
agent.
References:
1. Snow J. Cholera and the Water Supply
in the South Districts of London in 1854. J Public Health Sanit Rev.
1856;2(7):239-257.
2. Tulchinsky TH,
Varavikova EA, Cohen MJ. A history of public health. In: The New Public
Health. Elsevier; 2023:1-54. doi:10.1016/B978-0-12-822957-6.00009-0
3. Coleman TS.
Re-evaluating John Snow’s 1856 south London study. Soc Sci Med.
2024;344:116612. doi:10.1016/j.socscimed.2024.116612
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