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“Case Study I: Snow on Cholera”
Liberty University
HLTH485: Principles of Epidemiology and Biostatistics for Business(D01)
Professor Oswald Attin
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“Case Study I: Snow on Cholera”
A: Observations on cholera
1. How was cholera communicated regarding John Barnes? What were the modes of disease
transmission? What is the correct epidemiological term for the modes of transmission
identified?
In John Barnes' studies of cholera, the disease was passed on primarily through
contaminated water. Among the modes of transmission identified were waterborne transmission
and fecal-oral transmission. This occurred when people drank water or ate food that had
contaminated different Vibrio cholera bacteria. They are divided into two main transmission
groups that are transported by water or food and are referred to as "vehicle transmission" in
epidemiology.
2. How long is a fortnight?
It is a 2-week period of 14 days,
3. In the examples of circumstances presented, what were the various modes of transmission
stated or at least alluded to? Which were correct? Which were incorrect and why? What
role did personal hygiene and sanitation (including food preparation and hand washing)
play in transmitting the disease and continuing an outbreak?
Waterborne and fecal-oral routes were mainly the routes of cholera transmission. Dr.
John Snow pinpointed that the wells with contaminated water were the source of the outbreak,
and another well was contaminated by drainage from cesspools. Snow could not say that human-
to-human transmission played a role in human transmission endings. Poor sanitation, including
contaminated water sources, was at the heart of the outbreak transmission; for this reason,
improving sanitation services and promoting hygiene practices are necessary to avoid cholera
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outbreaks. Several instances of causal association were presented or alluded to in the examples
presented in the case.
4. List the various instances of association you can identify from the examples or situations
presented in the case. What role did social class, poverty, and housing arrangements play
in the association? What role did water play in the association?
Existing causal relationships between the various factors and the case of cholera
outbreaks were brought to light. Firstly, the quality of water sources was communicated through
the case of polluted water points and wells, which are directly connected to the spread of the
disease. Apart from that, the sanitation system was another vehicle of cholera transmission in the
communities because of shared wells among different families. Apart from this, social class and
poverty also played alongside vulnerability to cholera because areas that had insufficient
sanitation facilities had been found to have higher rates of infections in poor neighborhoods. The
condition of water sources polluted by shit and drain sewers happened to be a reminder of the
influence of poverty in worsening sanitation problems.
5. Describe the disease cholera as presented in the Snow case. Describe cholera as it is
known today.
The death toll in the cholera cases of Snow was severe as it took many lives and caused
symptoms like diarrhea, vomiting, and dehydration. The ignorant citizens believed that the water
was the primary medium through which the disease was transmitted, which caused many
epidemics in the cities. Today, cholera, transmitted by Vibrio cholera bacterium through polluted
water and food and turned out to be an acute diarrheal disease, is still a matter of the attention of
the World Health Organization. Nowadays, improved water and sanitation facilities, clean water
access, and oral rehydration therapy have markedly reduced the mortality of Charlotte.
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6. What hypotheses did John Snow develop about the cause (etiology), signs and symptoms,
spread, and course of cholera? How do Snow's observations and hypotheses conform
with understanding and knowledge of cholera?
John Snow assumed that cholera originated in infected water, thus producing severe
diarrhea and dehydration. He observed waterborne transmission around a water-healthy area,
confirmed by spatial clustering of the cases. Snow's theories align with modern comprehension
because cholera is a disease caused by the bacteria Vibrio cholera, which mainly transmits
through the water and in which patients suffer from watery stool and dehydration.
7. What is different about those who develop cholera compared with those who do not?
The outbreak is anticipated to reach a community that uses the contaminated water or
foods for drinking or cooking. Vibrio cholera bacteria cause diarrhea and dehydration. The other
people who do not have this pathogen remain healthy.
8. For example, what epidemiological phenomenon can be observed in Locksbrook, near
Bath?
The Locksbrook case conveys the well-defined epidemiological pattern called spatial
clustering when cholera cases are situated close to a hazardous water source and demonstrate a
localized outbreak linked to a specific environmental exposure.
B: Cholera and the Broad Street Outbreak
1. What are the time factors and implications for this case? Explain the time lag from
attacks in Figure I.2 to Deaths in Figure I.3.
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The time parameters in the Broad Street outbreak indicate a delay between the onset of
complaints (symptoms) and deaths, which implied that the disease had progressed. This time lag
provided an opportunity to trace the outbreak based on deaths, thus enabling John Snow to
investigate the source of the cases.
2. What are the place factors and implications for this case? Compare the workhouse to the
brewery to the pub. Discuss migration and its effect on the epidemic. What place issues
are essential to this case?
The location factors in the Broad Street cholera cases are critical in knowing how the
disease spreads. When comparing the workhouse, brewery, and pub, it becomes apparent that the
locations vary considerably in the extent to which they are exposed to contaminated water
sources. The workhouse, which uses water from an alternative source, has more cases than in
locations like the brewery and pub, where using water from the Broad Street pump has led to
higher infection rates. The migration may have helped spread this disease since the disease could
have spread along with the movement of the people between different places acting as the
transmitters. The crucial points are the nearness to water sources polluted with contaminated
water, alterations in water-consuming behaviors, and the migration of people from one point to
another, which changed the course of the epidemic.
3. What did the healthy persons do differently than the ill—those who got the disease (for
example, the inmates in the workhouse)?
The survivors of the outbreak, those who had not consumed water from the Peak Street
well, definitely fell into this category. They did not get water from the river but from alternative
sources. On the contrary, the people who were sick drank water from the contaminated wells,
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and that was how the cholera had infected them. Consequently, the prerequisite is in the selection
of water supply.
4. What is the index case from Figure I. 2? What date is the beginning of the epidemic?
What other time factors are discerned from this chart? How did Snow establish the time
Snow onset?
In Figure I. 2, the index case denotes the first reported cholera case among Broad Street
borough residents. The commencement of the epidemic is manifested by showing the outbreak
symptoms in this index case dated 28 August. Besides those time factors, visible on the chart, a
line shows the advancement of cases over time and how the disease spreads. Snow attributed the
onset time by introducing the two phenomena, i.e., the onset of symptoms with water
consumption from the Broad Street pump. Through tracking the symptoms and beginnings of
people, Snow was able to have of the outbreak and consequently the spread patterns.
5. What accurate observations were made about wells, cesspools, and groundwater, the
purity of the water, and its contamination? What inaccurate and misunderstood
observations about the water, its flow, and its contamination were made?
The reports, which accurately described different pollution sources, including wells,
cesspools, and groundwater supplies, made people think that it was where the drinking water
pollution came from. Dr. John Snow had localized the Broad Street pump as the primary source
of the cholera epidemic as it consisted of contaminated wastewater. Nevertheless, incorrect and
misleading observations entailed the idea that water flowing through the ground was purified,
prompting some to oppose the theory that water not of good quality could lead to disease. There
were also misunderstandings related to water pollution and purification mechanisms. Some
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people attribute mystical forces or the unseen to water quality while failing to understand the role
of sewage and pollution in the transmission of waterborne diseases.
6. What evidence did Snow use to establish that the cholera epidemic was occurring? Did
Snow demonstrate the cause and source of the cholera outbreak in the Golden Square
area? Explain.
Dr. John Snow located the cholera outbreak around the Broad Street pump via a spatial
mapping demonstrating the concentration of cases around that neighborhood. Through
interviews with the residents and observing water usage, he isolated the common factor: reliance
on the water pump in all the affected individuals. Snow's comparison with regions unaffected
confirmed his diagnosis, as those using alternative water sources did not have the same
outbreaks.
7. What were Snow's initial and primary hypotheses concerning the epidemic? What
processes and procedures did Snow use to establish hypotheses (prove or disprove them)
about the outbreak?
Dr. John Snow assumed that the Broad Street pump's water could cause the cholera
outbreak. He surmised that the disease spread by consuming water from this pump was more
likely to be cholera. Snow relied on spatial mapping, interviews with the affected people, and
comparisons between areas where the water was clean and those with contaminated water to
check or disprove these hypotheses. Consequently, he established a strong relationship between
the contaminated water from the Broad Street pump and the number of cholera cases.
8. The apparent control measure was removing the handle from the Broad Street pump.
What role did the removal of the pump handle play in the epidemic's decline? Did it
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affect the control epidemic? What other social and political roles did removing the handle
from the pump play?
The Broad Street pump handle was nearly the reason for the drop in the epidemic,
stopping any further access to polluted water. This means that the transfer of cholera from the
source was stopped, as evidenced by the reduction in new cases. On the social side, it excited
people to act and be more conscious about the health measures needed to avoid the recurrence of
epidemics. Thus, it politically pressured authorities to look into sanitation crisis issues and
infrastructure improvement to block future outbreaks.
C: Cholera Epidemic of 1853 and Two London Water Companies
1. What are the various aspects of the person presented in the above water company case
concerning the cholera epidemic, especially as the person concept relates to the
households that received the water supplies compared to those who used different water
supplies?
In the water company's case against the cholera epidemic of 1853, the person concept is
brought to the fore by inequality in clean water access between places where people live. The
town's residents, supplied with water by water companies, thought the water to be naturally pure,
while others relied on the potentially polluted sources. Hence, the biased distribution of water
sources influenced the cholera transmission rates and affected people's health differently during
the epidemics. Such a gap indicates that equal access to clean water will be critical in preventing
water-related diseases, such as cholera.
2. Explain the soundness of the research approaches regarding the water supply system and
structure of the two different water companies. Is this a descriptive or analytic
epidemiologic research design?
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The research methodology adopted to study both water companies' water supply systems
and structures was proven sound and practical. Researchers can compare households from the
two companies and then find cholera incidence rates to estimate the impact of water quality on
disease transmission. This statistical approach is considered both descriptive and analytic
epidemiologic research. Descriptively, it was the distribution of cholera cases across households
according to their water source. Analytically, it intended to find the connection between cholera
infection rate and water quality; eventually, the study might discover a causal link between water
contamination and disease symptoms.
3. What were some of the practical problems and barriers that Snow faced that slowed
Snow's inquiry into the cholera epidemic of 1854? How would this relate to modern-day
epidemiological investigations?
Dr. John Snow encountered practical issues and obstacles during his investigation of the
cholera epidemic in 1854. Data insufficiency made it hard for him to draw a pathogen map and
find where it originated. He succeeded despite resistance from local authorities and water
companies that his theory implicated contaminated water. Moreover, Snow's investigation has
limited research tools compared to current epidemiological studies, which may have further
hindered the effectiveness of his inquiry. However, Snow's perseverance and summative
techniques have set a milestone in epidemiology, as it has now been established that overcoming
obstacles is crucial for effectively controlling disease outbreaks.
4. "As the epidemic advanced, the disproportion between the number of cases in houses
supplied by the Southwark and Vauxhall Company and those supplied by the Lambeth
Company became not quite so great. . . ." From an epidemiological point of view, why
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was this so? Provide detailed epidemiological reasoning and discussion addressing the
issues of person, place, and time.
Regarding the epidemiological aspect, the gradually decreasing number of cases in the
Lambeth Company's neighborhoods was not associated with the overall number of households
supplied by the Southwark or Vauxhall Company. The first influenced factors are the population
composition and the distance to the sites where the contaminant was introduced, which may
explain the uneven cases in the beginning. Nonetheless, as the pandemic increasingly became
eminent, it is highly conceivable that cholera spread became almost equal among the populations
affected by companies, both static and dynamic, due to the wide spread of the pathogen, possibly
through contaminated water sources. Slowly, step by step, more people get engaged, and those
disparities are lessened. Finally, the distribution is expected to be fairer for all group concerns
D: Epidemiologic Issues
1. What did Snow observe regarding the association between city size and the epidemic
length?
While Snow compared the big cities with the smaller ones, he found that the larger ones
tend to have epidemics that last longer than those of the smaller cities. Such linkage implies that
aspects of city scale associated with population density and social contacts may be responsible
for the emergence and spread of these epidemics.
2. Snow suggested several reasons for the failure of contaminated water to produce disease
in all who consume it. Why did not everyone become sick or die when they consumed the
cholera-causing bacterium Vibrio cholera?
Snow cited several reasons, including dilution of the pathogen in water sources and
individual susceptibility to cholera, for why not all cholera patients have contaminated drinking
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water. Not everyone falls ill or dies due to Vibrio cholera consumption since personal immune
response, previous exposure to the bacteria, and general health conditioning make people
vulnerable to the bacteria and how the symptoms are expressed.
3. Which of Snow's observations about seasons and their effects on epidemics were correct,
and which were incorrect? Why?
Snow's observations of the impact of epidemics of time and seasons were, in most cases,
correct. He had indeed pointed out that the peak of cholera was usually during the warmer
period, possibly due to environmental factors like water temperature being favorable for the
growth of bacteria. Even though the idea of colder weather stopping the spread of cholera was
wrong, the disease may spread in colder climates and depends not only on warmer climates but
also on warmer temperatures for transmission.
4. Several different theories and hypotheses have been presented. Which are consistent with
known scientific and biomedical knowledge and common sense? Which of these are not?
Why?
Theories and hypotheses compatible with established scientific and biomedical
knowledge suggest that water contamination, bacterial infection, and host susceptibility explain
the outbreak and severity of cholera. These hypotheses are consistent with existing theory of
infectious disease transmission and pathogenesis. In opposition to this, those theories that claim
that cholera outbreaks are solely caused by miasma or "bad air" without any scientific evidence
and that do not match modern understanding of the disease's etiology and transmission routes are
not correct.
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References
Merrill, R. M. (2019). Introduction to Epidemiology (8th ed.). Jones & Bartlett Learning.
https://libertyonline.vitalsource.com/books/9781284203844
