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Observations on cholera
Question 1: Modes of Disease Transmission for John Barnes
According to Barnes, cholera is transmitted through handling contaminated items like the
clothing of a deceased cholera victim. The disease also spreads by touching contaminated objects
or surfaces, such as linen and clothing. The correct epidemiologic terms of the transmission
mode are direct contact and fomite transmission.
Question 2: Length of a Fortnight
A fortnight is a period of two weeks or 14 days (p. 259).
Question 3: Modes of Transmission in Presented Examples
Modes of transmission were transmission through contaminated garments and intercourse
with the persons suffering from cholera and also infection of water sources such as wells as in
case cholera patients use. Snow correctly identified Waterborne and direct contact transmission
courses as the key modes. His rejection concerning airborne transmission was well justified by
current evidence (p.259). Cholera grew and spread as a result of the low personal hygiene
standards and deficient sanitary conditions. Refusing to wash hands and poor food and water
management contributed significantly to the extension of the epidemic.
Question 4: Instances of Causal Association
Several instances of the causal association include the poor, living in crowded and
unsanitary conditions, being more susceptible to cholera. Housing arrangements such as
overcrowding increased the spread of the disease. Additionally, contaminated water sources and
improperly handled food were major vectors for cholera transmission.
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Question 5: Description of Cholera by John Snow and Today
John Snow stated that cholera is spread through material entering the alimentary canal,
initiating in the stomach and bowels. However, cholera is caused by the bacterium Vibrio
cholerae, leading to severe watery diarrhea due to enterotoxin.
Question 6: John Snow's Hypotheses on Cholera
He hypothesized that cholera was a morbid material that could replicate inside the body
of humans (p.259). The disease's signs and symptoms, spread, and course include gastrointestinal
distress, contaminated water, and rapid progression immediately after incubation. Snow's
hypotheses align closely with modern views, except his theory lacked the bacterial cause, which
was identified later.
Question 7: Contrast between Those Who Develop Cholera and Those Who Do Not
Those who develop cholera are those who are in direct exposure to cholera through
contaminated water or direct contact. Those who do not practice good hygiene, use clean water,
and do not directly contact the sick.
Question 8: Epidemiological Phenomenon in Locksbrook
The epidemiological phenomenon observed in Locksbrook is the water supply
contamination by cesspool drainage, which exemplifies an environmental pathway for disease
spread.
B: Cholera and the Broad Street Epidemic
Question 1: Time Factors and Significance
The histogram data of figures I-2 and I-3 depict the chronological occurrence of cholera
attacks and ensuing deaths. This is reflected in the peaks of attacks on September 1 and then
deaths on September 2, signifying the short incubation period of the illness (p.263).
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Question 2: Place Factors and Implications
The workhouse, brewery, and pub comparison show different levels of susceptibility to
contamination. The brewery workers remained healthy since they did not drink the water pump
instead, they drank the beer. Susceptible individuals migrated from the affected area, decreasing
the number of vulnerable people and slowing the spread. The main issues of places are the
location of water sources and population density.
Question 3: Well Persons vs. Ill Persons
The only difference was the water consumption.
Question 4: Index Case and Epidemic Onset
From Figure I-2, the index case appears around late August, but the significant increase
on August 31 marks the epidemic's onset. Snow established the onset by analyzing the sudden
spike in cases and linking it to water consumption from the pump.
Question 5: Observations on Water Contamination
The accurate findings included spotting organic impurities and linking the disease to
water from a particular pump. Underestimating how quickly cholera could contaminate water
became a problem due to the limited comprehension of bacterial pathogens at the time.
Question 6: Evidence of Epidemic and Source Identification
Snow used empirical data, mapping cholera cases across the water pump, and statistical
correlation to prove that epidemic. He finally proved it was the Broad Street pump through such
precise records that led to the discovery of the contamination source.
Question 7: Snow’s Hypotheses and Methodologies
Snow brought forward the sewer hypothesis and challenged the dominant miasma theory.
This was confirmed when he plotted cases, interviewed residents, and examined water samples.
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Question 8: Role of Pump Handle Removal
The cholera risk was drastically reduced by removing the pump handle, which verified
the outbreak's source and controlled it effectively. Politically, this move demonstrated a
government response to public health crises, encouraging public trust in future public health
measures.
Cholera Epidemic of 1853 and Two London Water Companies
Question 1
Households supplied by the Lambeth Company, which sourced water from Thames
Ditton free of London's sewage, experienced significantly fewer cholera cases than those
supplied by the Southwark and Vauxhall Company, which drew water contaminated with
sewage.
Question 2
Dr. John Snow’s approach was primarily analytical epidemiology. The research was
sound, using systematic data analysis and a natural experiment setting where two populations
unknowingly consumed water of differing quality, providing strong evidence of causality.
Question 3
Snow faced several practical difficulties in quickly obtaining accurate information on
which water company supplied each household, as residents often did not verify the receipts.
Modern epidemiological studies face similar issues, like data accessibility.
Question 4
As the 1854 cholera epidemic progressed, the initial distressing difference in cholera
cases between the groups supplied by different water companies receded somewhat. It could be
due to multiple epidemiological factors. Secondly, as soon as news about the pandemic began to
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spread, people could have taken personal precautions, like boiling water. In addition, the
alterations of cholera pathogen virulence or the collapse of immunity levels in communities may
as well have impacted the transmission dynamics of the disease. Water diversion or inadvertent
cross-contamination between the systems may have caused the more equal risk sharing over
time.
Epidemiologic Issues
Question 1
John Snow observed that the duration of a cholera epidemic in a locality was directly
proportional to its population size.
Question 2
Factors like the amount of contamination, the presence of cholera in visible particles that
could settle out of the water, and individual health conditions likely influenced whether a person
would contract the disease.
Question 3
Snow's observations about the seasonality of cholera were largely correct. However, his
specific observations on cholera behavior in Scotland, linking its spread to unboiled water used
with spirits, lack direct causation and might not fully capture other environmental or social
factors.
Question 4
Snow's hypothesis that cholera spreads through contaminated water is consistent with
modern scientific knowledge and was a significant departure from the miasma theory of disease,
which suggested transmission through bad air.
