HLTH 485
Case Study Assignment
Margaret Ochonu
HLTH485: Principles of Epidemiology and Biostatistics for Business
Liberty University
Professor John Griesenbeck
December 11, 2023
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CASE STUDY ASSIGNMENT INSTRUCTIONS
OVERVIEW
In order to master epidemiological concepts acquired in this course, it is imperative that
you understand how disease outbreak investigations work. You will be able to navigate a
real-life outbreak and solve important questions in relations to the case.
INSTRUCTIONS
You will find the case study titled: “Case Study I: Snow on Cholera” in the appendix I
section in the back of the textbook. Read the case study and answer all the questions below.
You must use complete sentences.
A: Observations on cholera
1. Concerning John Barnes, how was cholera communicated? What were the modes of
disease transmission? What is the correct epidemiological term for the modes of
transmission that were identified?
One of the casualties of the 1854 London cholera epidemic was John Barnes. The germs
that cause cholera may spread from person to person via tainted food or drink. During the
epidemic, two routes of transmission were identified: fecal-oral and waterborne. When an
infected person's feces gets into another person's mouth, this is called fecal-oral transmission. A
person may get this disease by ingesting tainted food or drink, or by coming into contact with
feces-contaminated surfaces and then touching their mouth. The cholera epidemic in London is
said to have originated in the polluted water supply from the Broad Street pump. When the
cholera bacteria are present in water sources that people drink, it may be transmitted to them by
waterborne means. The scientists believe that the water supply in London was contaminated by
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sewage from a cesspool that was located near to the Broad Street pump. This was the source of
the sickness spreading across the city via the water supply. When addressing the transmission
mechanisms that were identified during an epidemic, the appropriate word to use from an
epidemiological perspective is "routes of transmission." Several different modes of transmission
may be used to facilitate the spread of diseases from one individual to another. These modes
include direct or indirect contact, droplet transfer, airborne transmission, vectorborne
transmission, and droplet transfer. It was determined that fecal-oral and waterborne transmission
were the two principal mechanisms of transmission that were responsible for the cholera
pandemic that occurred in London.
2. How long is a fortnight?
The length of a fortnight is two weeks, or fourteen days. Originating from the Old English
word "feowertyne niht," meaning "fourteen nights," the modern English word "fortnight" comes
from the same root. In contrast to its relative rarity in American English, the word is widely used
in British and Australian English.
3. In the examples or 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 the transmission of the disease and
continuation of an outbreak?
Two routes of transmission were found in the case study "Snow on Cholera": fecal-oral and
waterborne. Since these two routes have been shown to be the most common ways that cholera
spreads, they were both right. The spread and persistence of the epidemic were mostly caused by
a lack of personal cleanliness and sanitation. Inadequate waste disposal and polluted water
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sources were examples of poor sanitation practices that contributed to the fast spread of cholera.
Lack of hand washing and incorrect food preparation are examples of poor personal hygiene
habits that also played a role in the disease's propagation. After the infected pump handle was
removed and the epidemic's cause was located, the outbreak started to fade. In order to stop the
transmission of contagious illnesses, it is crucial to maintain good sanitation and hygiene.
4. Several instances of causal association were presented or alluded to in the
examples presented in the case. 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 association? What role did
water play in association?
The case study "Snow on Cholera" provided or hinted at several cases of causal relationship.
Some examples are:
Cholera and polluted water: According to Dr. John Snow's research, the Broad Street
water pump was the origin of the polluted water that spread the disease throughout the
neighborhood.
The cholera epidemic mostly hit the poorest areas of London, where lack of cleanliness
and overcrowding contributed to the disease's rapid spread.
Because they had access to cleaner water and better living circumstances, the richer
Londoners were less impacted by the cholera epidemic, demonstrating the relationship
between socioeconomic class and the disease's spread.
Cholera was more easily transmitted in the congested and unclean circumstances of
London's tenements and slums, which is linked to housing arrangements.
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Furthermore, the link between these characteristics and the cholera outbreak was
significantly influenced by housing conditions, socioeconomic level, and poverty. The outbreak
disproportionately affected the most impoverished regions of London because to the high
population density and inadequate sanitation in those areas. The prevalence of the sickness was
lower among the affluent due to their ability to afford superior living conditions and access to
clean water. The fast spread of the sickness in London's tenements and slums was caused by
overcrowding and inadequate sanitation. This highlights the need of addressing socioeconomic
factors that influence health in order to prevent infectious disease outbreaks. The primary factor
contributing to the propagation of cholera was the contaminated water. The disease's
transmission to the area was facilitated by the polluted water originating from the Broad Street
pump. The rapid spread of cholera was also expedited by inadequate waste management and
contaminated water sources, both of which exemplified substandard sanitation standards.
5. Describe the disease cholera as presented in the Snow case. Describe cholera as it is
known today.
The bacterium Vibrio cholerae causes the acute diarrheal illness known as cholera.
Severe diarrhea, vomiting, and dehydration are symptoms of the sickness, which, if neglected,
may cause death within hours. According to the case study "Snow on Cholera," hundreds of
people died in a massive epidemic that hit London in 1854. Even in modern times, cholera
remains a major global health issue, especially in regions where sanitation is lacking and water is
scarce. The most common way for the illness to spread is via contaminated food or drink. If not
treated quickly, cholera, which causes severe diarrhea, vomiting, and dehydration, may be
deadly. In recent years, cholera prevention and treatment have made great strides. In places
where the illness is most likely to spread, people are taking an oral cholera vaccination.
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Additionally, cholera has become less common in many regions of the globe as a result of better
water and sanitation facilities.
6. What hypotheses were developed by John Snow about the cause (etiology), signs
and symptoms, spread and course of the cholera disease? How do the
observations and hypotheses of Snow conform with modern understanding and
knowledge of cholera?
While looking into the Broad Street epidemic, John Snow came up with a number of
theories on the cholera's origin, symptoms, transmission, and progression. Among these theories
were the following:
Contaminated water was the vector for the disease's transmission.
Symptoms of the illness included severe diarrhea, vomiting, and loss of fluids. In regions
with inadequate sanitation and high population density, the illness spread quickly due to
polluted water.
If the source of contamination could be located and removed, the sickness may be
stopped in its tracks.
Snow observed the epidemic and analyzed the facts he gathered to form his theories.
After doing extensive research, he determined that the Broad Street water pump was the culprit
responsible for the epidemic. To stem its spread, he suggested removing the pump's handle.
Everything that Snow thought about cholera—its origin, symptoms, transmission, and
progression—is in line with what is known today. The bacteria Vibrio cholerae is now known to
cause cholera and spreads via tainted food and water. In places where sanitation is lacking and
potable water is scarce, the illness may spread quickly, causing severe diarrhea, vomiting, and
dehydration. Additionally, current methods for cholera prevention and control stress the need of
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reducing the risk of transmission by enhancing water and sanitation infrastructure and locating
and eradicating the source of contamination. An important historical example of how public
health initiatives may be informed by epidemiological research and data analysis to prevent and
control infectious illnesses is the work of Snow about the Broad Street epidemic.
7. What is different about those who develop cholera compared with those who do
not?
Anyone may get cholera via drinking polluted water or eating contaminated food,
however certain people are more likely to get the disease than others. The likelihood of
contracting cholera may be affected by several circumstances, such as:
The danger of contracting cholera is increased in those whose diets include water or food
that has been polluted.
Areas with inadequate sanitation tend to have a higher occurrence of cholera because
people there are more likely to eat water and food that has been polluted.
Cholera is more likely to develop in those whose immune systems are already
compromised, such as those who are undernourished or suffer from other preexisting
health issues.
Research indicates that those with blood type O have a higher risk of contracting cholera
compared to those with other blood types.
8. What epidemiological phenomenon can be observed in the Locksbrook, near Bath,
example?
Clustering, often called geographical aggregation of patients, is an epidemiological
phenomenon that the Snow case study uses the Locksbrook example to demonstrate. Here, a
cluster of cholera cases along Bath's Locksbrook Road occurred in a short amount of time,
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indicating that the local population had a shared infection vector. Based on his research into the
epidemic, Snow determined that a cholera-infected pump on Locksbrook Road was the most
prevalent vector for the disease. His research showed that cholera cases were concentrated in the
immediate vicinity of the pump, whereas those residing farther away had a lower risk of
contracting the disease. Spatial clustering or aggregation is a common occurrence during
infectious disease outbreaks and may provide important information about the infection's origin
and transmission mechanism. Epidemiologists play a crucial role in the detection and
containment of infectious disease epidemics by spotting patterns of cases and looking into
possible shared vectors of transmission.
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.
In order to comprehend the public health consequences of the epidemic and its
progression, it is necessary to know the temporal variables associated with the Broad Street
cholera outbreak. In late August 1854, the first cholera cases were documented, and by
September, hundreds of cases had been recorded. According to Figure I.2, which displays the
distribution of attacks by date, the epidemic reached its peak in early September and then started
to diminish around the middle of the month. There is a lag between the beginning of the
epidemic and the peak of mortality, as seen in Figure I.3, which depicts the distribution of
fatalities by date. This is due to the fact that cholera may cause death within hours of infection,
but it may take many days for the illness to reach a stage where it becomes a serious health
concern. Deadly cholera may strike even days after the first symptoms appear. There was around
a week's delay between the Broad Street outbreak's assaults and fatalities. This indicates that the
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number of fatalities kept climbing until late September, when the epidemic started to fade, even
though the number of new cases started to fall in mid-September. The significance of early
diagnosis and action in disease outbreaks is underscored by this time lag, which has significant
consequences for public health. Early detection of cholera infections and the provision of
sanitation and safe drinking water are important public health interventions that may slow the
disease's spread and save lives.
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 important to this case?
To effectively identify the source of the pollution and conduct public health measures, it
was crucial to understand the topography of the region, which played a vital role in the Broad
Street cholera epidemic. The water pump on Broad Street was a significant location
consideration since it was close to several businesses, including the workhouse, the brewery, and
the tavern. The disease's impact varied throughout the people in these various areas. Because of
their age or physical condition, the numerous people living in the workhouse were at a higher
risk of contracting cholera. There was an increased danger of exposure to polluted water for the
many manual workers employed by the brewery. The locals often congregated in the tavern,
making it an ideal setting for the spread of the illness. Migration was another key place problem
during the pandemic. Overcrowding and inadequate sanitation were consequences of the rapid
population expansion and migration that was happening in London at that period. The cholera
epidemic was exacerbated by the fact that many of the ill people had come to the region in quest
of employment, which left them more exposed to the disease. These location considerations have
major ramifications. Numerous individuals were exposed to the illness due to the polluted water
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pump's close vicinity to the workhouse, brewery, and tavern. Further factors that aided the
disease's quick spread were the influx and outflow of people from the region and the city. Public
health authorities took action, including establishing more reliable supplies of clean water and
better sanitation, to address the environmental variables that aided the epidemic. They did their
best to inform the public about the dangers of cholera and how important it is to adopt good
sanitation and hygiene. In sum, the cholera epidemic on Broad Street shows how important it is
to think about where diseases spread, how people move about, and how urbanization affects
things like sanitation and living conditions.
3. What did the well persons do differently than the ill—those who got the disease (for
example the inmates in the workhouse)?
Even if some people who were exposed to the polluted water during the Broad Street
cholera epidemic did not become sick, others who were exposed to the same water did. It is not
yet known for sure what caused these variations, however there are a number of possible causes.
People who were able to avoid cholera may have had a preexisting immunity to the illness or a
more robust immune system than those who did. On the other side, those who became sick could
have suffered from compromised immune systems as a result of malnutrition, stress, or some
other issue. People who didn't get cholera probably took measures to shield themselves from the
water that was polluted. Some people may have taken precautions, such as boiling water before
use, or even abstained from water entirely, opting instead for alcoholic drinks like beer, which
were seen as less harmful. There may have been more variables that made the workhouse
prisoners more vulnerable to cholera. One possible factor that contributed to the high risk of
disease transmission in the workhouse was the overcrowding and lack of proper sanitation.
During the Broad Street epidemic, it is hard to say for sure what the healthy people did
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differently from the sick. But it's obvious that immunity, diet, and exposure to polluted water
were all variables in deciding who got sick and who didn't. Another important component in the
disease's spread was the variation in people's living situations and hygiene habits.
4. From Figure I.2, what is the index case? What date is the beginning of the
epidemic? What other time factors are discerned from this chart? How did Snow
establish the time of onset?
In Figure I.2, we can see the spread of the Broad Street cholera epidemic by date. Since
the data only starts on August 19, 1854, after several instances have already been recorded, it is
impossible to pinpoint the index case—the first person to get infected with the disease—from
this figure. The sharp uptick in reported cases in late August and early September, however,
provides a good indication of when the pandemic first started. From August 31 to September 2,
the number of cases increased sharply, and from September 2 to September 7, the number of
cases peaked. These findings point to the beginning of the outbreak in either late August or early
September. The figure also shows other time-related variables, such as the length of the epidemic
and its pace of spread. The outbreak peaked in the second week of its roughly three-week
duration. Since the curve exhibits a sharp spike in instances followed by a steep fall, we may
deduce the rate of spread from its form. After meticulously analyzing the data, Snow determined
when the outbreak began. He looked at how many instances there were by year and region,
among other things, and at the impacted people and their living circumstances. He gathered
information about the disease's impact from interviews with survivors and utilized it to formulate
a theory on the epidemic's origin. With this information in hand, Snow could determine when the
disease began and pinpoint its origin to the polluted water pump on Broad Street.
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5. What accurate observations were made about wells, cesspools, and ground water,
the purity of the water, and its contamination? What inaccurate and misunderstood
observations were made about the water, its flow, and its contamination?
Several valid points about the origins and spread of cholera were raised during the Broad
Street epidemic. As an illustration:
It was John Snow's observation that several sick people had drunk water from the Broad
Street pump that led him to conclude that this was the wellspring of the epidemic.
A Snow also pointed out that the well the pump used to draw water from was near a
cesspool, which meant that the water might have been polluted with cholera-causing
germs in the feces.
Additionally, Snow noted that there were no cholera cases among the neighboring
brewery dwellers who had their own well and did not use the pump on Broad Street.
According to Snow, the water from the Broad Street pump was the main culprit in the
cholera epidemic, and he reasoned that polluted water was the main way the disease was spread.
On the other hand, certain statements on the water and its contamination were erroneous and
poorly understood. To illustrate the point, not everyone agreed that polluted water was the vector
for the spread of cholera; others thought the disease spread via miasma, or filthy air. The
development of sewage systems, which removed garbage from cities and towns but did nothing
to treat or dispose of it correctly, was prompted by this hypothesis.
Misunderstandings about groundwater movement and contamination also occurred. Some
people thought, for instance, that water seeping into the ground from above via layers of rock
and silt was filtered out by the soil. But that wasn't always the case; cesspools and animal feces
were among the pollution sources that may taint groundwater.
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Misunderstandings about the quality of various water sources also occurred. For instance,
there were those who held the view that river water was perpetually polluted, while others
maintained the view that well water was intrinsically clean and safe to drink. Nevertheless, the
closeness of water supplies to pollution sources, the availability of treatment or filtration
systems, and the general cleanliness and sanitation habits of the people using the water all had a
role in determining the water's safety.
6. What evidence did Snow use to establish the fact that a cholera epidemic was
occurring? Did Snow clearly demonstrate the cause and source of the outbreak of
cholera in the Golden Square area? Explain.
During the Broad Street outbreak, John Snow presented many pieces of evidence to prove
that cholera was rampant. Some of them were:
By breaking down the number of cases by time and place, Snow was able to pinpoint
exactly when and where the epidemic was at its worst.
A Snow was able to collect more specific information on the symptoms and beginning of
the sickness via interviews with people who had been impacted by it.
A The cholera incidence rates in various communities were compared so that Snow could
make conclusions on the mechanism of transmission. For example, he compared the
people that utilized the Broad Street pump with those who did not.
7. What were Snow’s initial and basic hypotheses concerning the epidemic? What
processes and procedures did Snow use to establish his hypotheses (prove or
disprove them) about the outbreak?
As Snow proved, the pollution of the water supply originated at the Broad Street pump,
which in turn caused the epidemic. Specifically, he demonstrated that cholera was not an issue
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for those who had access to their own water sources, such as the neighboring brewery's
inhabitants, and that most of the sick had drunk from the pump. Snow also showed that the well
the pump used to draw water from was near a cesspool, which might explain how the water
became polluted. Although Snow's data was inconclusive, it was sufficient to back his theory
that the epidemic was caused by polluted water, with the Broad Street pump being the particular
point of contamination. The presence of cholera germs in the water from the Broad Street pump
was subsequently verified by laboratory testing of water samples, lending credence to this idea.
In order to back up his theory that the epidemic was caused by polluted water from the Broad
Street pump, Snow collected a mountain of data and proof. Additionally, he was successful in
debunking competing hypotheses, such as the miasma hypothesis, which proposed that airborne
pollutants were to blame for the illness. In order to formulate his theories on the origin and cause
of the cholera epidemic and to collect data to back up his claims, Snow used a mix of
environmental elements, laboratory analysis, and epidemiological approaches. The germ
hypothesis of illness and contemporary epidemiology owe a great deal to his groundbreaking
research.
8. The obvious control measure applied was the removal of the handle from the Broad
Street pump. What role did the removal of the pump handle play in the decline of
the epidemic? Did the removal of the pump handle have an effect on the control
epidemic? What other social and political roles did removing the handle from the
pump play?
One of the most important control measures that contributed to the epidemic's reduction
was taking the handle off the Broad Street pump. The authorities successfully halted the disease's
spread by prohibiting the public from using the pump and consuming the polluted water. New
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instances started to fall within days of the pump handle being removed, and the pandemic was
finally brought to a close. Due to its simplicity, effectiveness, and rapid implementation, taking
the handle off the pump probably made a big difference in controlling the pandemic. On the
other hand, alternative forms of control, including cleaning polluted water or enhancing
sanitation, would have required more effort and time to execute. There were significant social
and political functions for removing the pump handle beyond its practical use in containing the
outbreak. For instance, it provided support for John Snow's contention that the epidemic was
caused by polluted water, with the Broad Street pump being the particular point of
contamination. Given that Snow's idea had encountered early pushback and criticism from some
individuals within the medical establishment, this was a significant accomplishment for him. The
significance of government involvement in public health emergencies and the efficacy of public
health interventions were further highlighted by the removal of the pump handle. It paved the
way for subsequent public health programs and interventions by demonstrating the potential
involvement of governments and public health authorities in safeguarding the health and welfare
of their populations.
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 epidemic of cholera, especially as the person concept relates to
the households which were recipients of the supplies of the water as compared to
those who used different water supplies?
Regardless of where they live or their family's financial situation, it is this person's
responsibility to guarantee that all homes have access to clean water. Keeping the water supply
system efficient and dependable so that all homes can count on constant water delivery is an
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important part of this. Another crucial part of this person's job is to keep an eye on the water
supply and do everything they can to stop pollution and illnesses that are transmitted via water.
This can include doing things like filtering or chlorinating the water or testing samples on a
regular basis to make sure it's safe to drink. During a cholera outbreak, the person in charge of
the water supply would have to be extra careful to protect the homes that were getting water
from the polluted Broad Street pump and stop the illness from spreading to other homes. One
option is to turn off the pump, while another is to provide impacted families with other ways to
get clean water. In order to play a crucial role in avoiding the spread of waterborne illnesses like
cholera, the person in charge of the water supply must take certain variables into account. The
availability of potable water for all residents, regular testing of water quality, and other
precautions to avoid pollution and disease transmission are all part of this category.
2. Concerning the water supply system and structure from the two different water
companies, explain the soundness of the research approaches. Is this a descriptive
or analytic epidemiologic research design?
The investigation of the cholera pandemic in London included a combination of descriptive
and analytic epidemiologic research methodologies. Descriptive epidemiology entails gathering
and examining data to depict the spread and attributes of a specific disease or health condition
among a population. On the other hand, analytic epidemiology employs statistical techniques to
evaluate hypotheses regarding the causes and risk factors of a disease. During the cholera
pandemic, John Snow used a descriptive epidemiological method to chart the geographical
spread of cases and pinpoint possible sources of contamination, such as the Broad Street pump.
The individual gathered data on the geographic coordinates and quantity of cholera instances,
and used this data to construct a map that showed a distinct concentration of cases in close
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proximity to the pump. By providing detailed descriptions, the location and scope of the
epidemic may be pinpointed, and crucial information on the possible contamination source might
be uncovered. To further support his claim that the cholera epidemic originated from the polluted
water supplied by the Broad Street pump, Snow used an analytical epidemiologic methodology
to examine the possibility. homes supplied water by the Southwark and Vauxhall Company had
far lower cholera rates than those supplied by the Lambeth Company, according to his
assessment of cholera rates among homes receiving water from other businesses. Snow was able
to prove his theory and show that the polluted water supply was associated with the spread of
cholera by using this analytical method. Because of its innovative and methodologically solid
research methods, Snow's work was essential in launching epidemiology into the mainstream of
scientific inquiry. His data collection and analysis techniques served to prove the value of
thorough research in public health, and the insights he offered on the spread and causes of
cholera were invaluable. In sum, the cholera pandemic inquiry made use of solid research
methodologies that will continue to shape epidemiology.
3. What were some of the practical problems and barriers that Snow faced which
slowed his inquiry of the cholera epidemic of 1854? How would this relate to
modern day epidemiological investigations?
While investigating the 1854 cholera pandemic, John Snow encountered several logistical
challenges. The absence of uniform methods for gathering and reporting data was a major
obstacle for him since it made it hard to get reliable details on the spread of the epidemic.
Furthermore, effective control measures could not be developed due to the lack of understanding
about the transmission and causes of cholera during that period. The local government and water
corporations were hesitant to accept Snow's claim that the outbreak was caused by tainted water,
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which was another obstacle he had to overcome. The acceptance of Snow's findings was delayed
due to this reluctance, which made it harder to adopt control measures like removing the Broad
Street pump handle. These real-world challenges and obstacles that Snow encountered when
studying the 1854 cholera pandemic are still pertinent to contemporary epidemiological studies.
For reliable and consistent results, standardized methods of data collecting and reporting are still
required, and local authorities and other stakeholders may be reluctant to embrace new
information or embrace control mechanisms. Contemporary epidemiologists, however, may
make use of analytical tools and technology that were previously unavailable, thus they are able
to circumvent some of these limitations. To swiftly and reliably gather and analyze massive
volumes of data, for instance, digital data gathering techniques and geographic information
systems (GIS) are useful. Also, results and suggestions may be sent far and wide thanks to
today's communication technology. Although there have been some improvements, there are still
many obstacles and practical issues that epidemiologists have when trying to investigate disease
outbreaks. Public health organizations and researchers must persist in their pursuit of better
methods of disease outbreak detection and control.
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 was this so? Give detailed epidemiological reasoning and discussion
addressing person, place, and time issues.
The remark implies that as the pandemic advanced, the disparity in case numbers
between houses receiving water from the Southwark and Vauxhall Company and those supplied
by the Lambeth Company started to diminish. From an epidemiological perspective, there might
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be several factors contributing to this phenomenon. Initially, it is plausible that the disparity in
the number of cases across houses supplied by the two water companies was attributable to
variations in the populations serviced by each firm. For instance, if the community serviced by
the Southwark and Vauxhall Company had a greater incidence of risk factors for cholera, such as
inadequate sanitation or overcrowding, it would be anticipated that a larger number of cases
would arise in this group initially. Though the disparity in case counts may have shrunk at the
outset, it's plausible that the epidemic's risk factors grew more uniformly distributed throughout
the two firms' customer bases as it continued. In addition, the water pollution may have
happened at several locations throughout the distribution network, rather than being limited to
just one firm or source. There may have been a decline in the disparity between the two
businesses' initial case counts as the outbreak continued since homes served by both providers
were exposed to polluted water. Furthermore, it is possible that control measures, such as the
removal of the Broad Street pump handle and improvements in sanitation, had a greater impact
on reducing the spread of cholera than the specific source of the contaminated water. As these
measures were implemented, it is possible that the difference in the number of cases between
households supplied by the two companies decreased. It is important to consider person, place,
and time factors when investigating disease outbreaks, as they can provide valuable insights into
the transmission and spread of the disease. Given the disparities in the populations served by the
two water companies and the possibility of contamination at various points in the water
distribution network, it is possible to explain why the initial disparity in the number of cases
between households supplied by the two companies decreased as the cholera epidemic of 1854
progressed.
D: Epidemiologic Issues
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1. What did Snow observe regarding the association between city size and the length of
the epidemic?
According to Snow, the duration of a cholera outbreak in a city was proportional to its
population. In particular, he pointed out that cholera outbreaks often lasted longer in bigger cities
compared to smaller ones. This conclusion was drawn by Snow from his research on cholera
outbreaks in several English cities. He made the observation that cholera outbreaks in smaller
towns usually subsided after a few weeks or so. There may be months—if not years—long
cholera outbreaks in major cities. This finding might be explained in a number of ways. One
issue is that it might be more difficult to detect and manage the source of pollution in bigger
cities due to the more complicated water delivery networks. Furthermore, sickness might be
more easily disseminated in highly populated parts of bigger cities. It should be mentioned that
Snow made these findings in the middle of the nineteenth century, thus the elements that affect
the spread and duration of cholera outbreaks could have altered since then. Nevertheless,
contemporary epidemiological research owes a debt of gratitude to his efforts in tracing the
transmission of cholera to variables like water availability and sanitation.
2. Snow suggested several reasons for the failure of contaminated water to produce
disease in all who consume it. Why is it that not everyone became sick or died when
they consumed the cholera-causing bacterium Vibrio cholera?
The inability of polluted water to infect everyone who drinks it was explained by Snow in
a number of ways. The fact that not all people infected with Vibrio cholerae really became ill or
died is due to a number of factors:
Due to prior exposure, some people may have acquired a resistance to cholera. This can
be because of an innate resistance or because of past experiences with a less severe
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The likelihood that a person may get cholera depends on the dose of Vibrio cholerae that
they consume. Some people may not have been sickened because they did not ingest
enough of the bacterium.
Factors affecting the host: A person's risk of contracting cholera may be impacted by
their age, health, and genes. Some people may have weakened immune systems and
hence be more prone to contracting the illness.
Cholera epidemics may be accelerated or exacerbated by environmental variables like
humidity and temperature.
3. Which of Snow’s observations about time and seasons and their effects on epidemics
were correct and which were incorrect? Why?
When asked about the impact of the passing of time and seasons on epidemics, Snow offered
several findings. Some of these points were spot on, while others needed some work.
Correct observations: Evidence from several infectious illnesses, including cholera, supports
the idea that epidemics tend to occur more often during the summer months. The summer months
might be particularly conducive to the spread of infectious illnesses due to the high humidity and
warm temperatures. The data from many cholera outbreaks supports the notion that cholera is
more common in metropolitan environments. The illness may spread more easily in urban
settings due to the higher population density and less hygienic circumstances.
Incorrect observations: According to Snow's miasma theory of illness, cholera may be
transmitted by breathing in certain unpleasant scents. Now that we know that contaminated water
or food is the main vector for the transmission of cholera, this notion has been debunked.
According to Snow, alterations in atmospheric conditions, such shifts in temperature or
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humidity, may set off cholera epidemics. Cholera mostly spreads via contaminated water or food,
however environmental variables may also play a role.
4. Several different theories and hypotheses have been presented. Which of these are
consistent with known scientific and biomedical knowledge and common sense?
Which of these are not? Why?
Theoretical and empirical claims in this case study varied in their degree of congruence with
established biomedical and scientific facts as well as with common sense. Let me give you a few
instances:
In line with conventional wisdom and established biological and scientific facts:
It was reasonable and supported by science that Snow postulated polluted water was the
root cause of cholera.
Consistent with established biomedical knowledge, Snow noted that not everyone who
drank polluted water got ill or died.
According to established biomedical knowledge, Snow correctly noted that the outbreak
had various effects on those who drank polluted water from different sources.
Discordant with conventional wisdom and established biological and scientific facts:
The miasma idea, which postulated that unhealthy air was to blame for the pandemic, was
one of many competing hypotheses that failed to take into account current scientific
understanding.
A Claims that certain foods, such bread or cheese, were to blame for the outbreak ran
counter to what was understood at the time in the field of biomedicine.
After doing his own research, Snow came to the conclusion that the miasma produced by
sewage breakdown was not the cause of the outbreak, which ran counter to what was
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recognized in the scientific community. Theories that were previously thought to be true
may be proven or refuted as scientific understanding develops throughout time. That is
why we should always be open to fresh information and revise our views appropriately.
Note: Your assignment will be checked for originality via the Turnitin plagiarism tool.
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