Epidemiology

State or paraphrase the content of John Snow's famous quote.

"The point is that, although it is extremely important for us to maximize our knowledge of the biology and pathogenesis of disease, it is not always necessary to know every detail of pathogenesis to be able to prevent a disease."

Explain what 'doing no harm' means.

'Doing no harm' relates to the ethical value known today as 'nonmaleficence', which means not making a patient's injury worse than it already is.

Summarize John Snow's achievements.

* John Snow linked the cholera outbreak in London to contaminated water from certain water supply companies. * Snow tested his hypothesis that it was contaminated water leading to the cholera disease. * Through collecting data door-to-door, Snow was able to chart the frequency and distribution of the disease. * John Snow was the first person to draw the three components of epidemiology together.

What are the objectives of epidemiology?

1. To identify the cause of disease. 2. To determine the extent of disease found in a community. 3. To study the natural history and prognosis of disease. 4. To evaluate both existing and newly developed preventive and therapeutic measures and modes of health care delivery. 5. To provide the foundation for developing public policy relating to environmental problems and other considerations regarding disease prevention and health promotion.

Does a screening diagnose an illness?

A screening does not necessarily diagnose an illness; there must often be further evaluation.

What does changing the cut off level regarding continuous variables do?

Changing the cut off level regarding continuous variables changes the sensitivity & specificity.

What are the consequences of choosing certain cut offs?

Consequences of choosing cut offs include having undetected cases of illness and telling a person that they are ill when they really are not.

What are continuous variables? Give examples.

Continuous variables are variables for which there is no positive or negative result. A decision must be made in establishing cut off levels. Examples of continuous variables include: blood pressure & glucose levels.

Explain more about what Jenner discovered concerning smallpox contraction.

Edward Jenner discovered that cowpox contraction could prevent smallpox contraction.

Who was Edward Jenner, and what was he known for?

Edward Jenner lived in the 1700s in England and he became very interested in the problem of small pox, a disease which affected the whole world at that time. In the late 1700s, approximately 400,000 people died from smallpox each year and a third of survivors became blind as a result.

Can rheumatic fever be prevented?

Even without fully understanding the chain of pathogenesis from infection with streptococcus to rheumatic fever, we can prevent virtually every case of rheumatic fever if we promptly and adequately treat streptococcal infections.

Give examples of screenings for various diseases and the variables associated with them?

Examples of these biological variables include: * Hga1c and blood glucose regarding diabetes screening; * Antibody presence regarding HIV screening; and * Blood pressure regarding high blood pressure and hypertension screening.

Why are false negatives a problem?

False negatives are a problem because if a person has a disease & they believe that they do not they might not seek treatment or they might seek treatment too late. For example, certain cancers must be treated in the early stages to be properly cured.

What are false negatives?

False negatives are people with a disease that are falsely called negative.

Talk about the consequences and costs of false positives versus false negatives.

False positives are associated with costs, both emotional and financial, and false negatives are associated with delayed or nontreatment of serious disease.

What is a false positive?

False positives are people without a disease who are falsely called positive.

What points are contained within the Hippocratic Oath?

Found within the Hippocratic Oath are; * values regarding treating the ill to the best of one's ability; * maintaining patient's privacy; and * teaching medicine to the next generation.

Draw a diagram of the above concerning true and false negatives and positives.

Have the Disease Do Not Have the Disease Positive: True Pos. False Positive Negative: False Neg. True Negative

Name something else that was especially important that Hippocrates wrote about in the Hippocratic Oath?

Hippocrates also wrote about the value of 'doing no harm'.

Who is Hippocrates and what is he known for?

Hippocrates is an ancient Greek physician who is known as the father of medicine.

What is Hippocrates especially known for?

Hippocrates is especially known for his medical ethics, particularly those found within the Hippocratic Oath.

What did Hippocrates say about privacy?

Hippocrates said that: "Whatsoever I shall see or hear of the lives of men and women which is not fitting to be spoken, I will keep secret."

Give more information concerning a high cut off level.

If a high cut off level is chosen then it is more accurate for specificity but less accurate for sensitivity.

Give more information concerning a low cut off level.

If a low cut off level is chosen then it is more accurate for sensitivity but less accurate for specificity.

Explain about multiple tests and the categories.

If multiple tests are done, these tests can be put into two categories. These two categories are serial testing and parallel testing, and these two categories differ in procedure and effect.

Who was Ignaz Semmelweis and what did he do?

Ignaz Semmelweis was a medical doctor in Austria in the 1800s. Semmelwies specialized in obstetrics and became interested in a major clinical and public health problem of the day, which was childbed fever, also known as puerperal fever.

Who was D.A. Henderson directed the World Health Organization's Smallpox Eradication Program in 1967.

In 1967 the W.H.O. began international efforts to eradicate smallpox using vaccinations with cowpox.

How is the gold standard used?

In order to properly calculate the sensitivity and specificity of a test we must compare this data against the gold standard.

What happens when we use a test in real life?

In real life, when we use a test to identify diseased and non-diseased persons we clearly do not know who has the disease & who does not. To begin to assess the sensitivity & specificity of a test we must have another source of truth with which to compare the test results.

What was childbed fever?

In the 1800s, childbed fever was a major cause of death among women shortly after childbirth, with rates as high as 25%.

Had anything been known about the origins of cholera prior to John Snow?

No, at the time prior to John Snow, nothing was known about the biology of the disease.

Was James Lind's conclusion concerning the cause of scurvy accepted by authorities right away?

No, it was not until 47 years later, when James Lind's was able to repeat the experiment on the entire naval fleet, that his finding of a dietary cause of scurvy accepted.

Explain how John Snow began to develop his theory.

One of the water companies moved their company from Central London to further upstream outside the city. Snow reasoned that the Lambeth Company, which moved to a less polluted part of the river would provide water that would make less people sick than in the more contaminated part of the river.

What is parallel testing?

Parallel testing is when two screening tests are performed at the same time and the results are subsequently combined.

Explain how people in London got their water during John Snow's time.

People at the time got their water by signing up with a water company, and these companies drew their water from the Thames River.

How does screening relate to prognosis?

Regarding screening, early detection leads to a more favorable prognosis.

What are screenings designed to do & on what?

Screenings are designed to separate people with a disease from people without a disease based on biological variables.

Where and when did Semmelweis practice?

Semmelweis became in charge of the First Obstetrical Clinic for the General Hospital in Vienna in 1846. (There happened to be two obstetrical clinics for the general hospital, the first and the second, and women were admitted for childbirth to the first or second clinic on an alternating basis.)

What did Semmelweis theorize concerning the cause of childbed fever, including the solution?

Semmelweis correctly theorized that doctors were carrying disease particles on their hands because of this practice of doing autopsies around women in childbirth. Semmelweis tried to prevent this & was successful for a time by requiring doctors and medical students to was their hands before assisting patients.

What is sensitivity?

Sensitivity is defined as the ability of the test to identify correctly who has the disease.

What is serial testing?

Serial testing is when the second screening test is performed only if the result of the first screening test is positive.

What are some factors when screenings should be done?

Some of the factors when screenings should done include: * 1. With diseases that have subclinical periods; * 2. Diseases where early treatment is beneficial; * 3. If a valid and reliable test is available; * 4. If a test is low risk, this means, cheap, easy to use, & minimally instrusive; * 5. If a test is feasible, this means if the population is willing to do it; * 6. If the disease is serious, meaning fatal or highly impactful to life

How can specificity be determined?

Specificity can be determined by dividing true negatives by false positives plus true negatives and multiplying it by 100.

What is specificity?

Specificity is a measure of validity that is described as the ability of a test to correctly identify people without a particular disease.

What is the Hippocratic Oath?

The Hippocratic Oath is a Code Of Conduct which many medical professionals have used for over the course of many centuries, and it is still used today by medical doctors.

What are the problems caused by false positives?

The problems caused by false positives include a burden on the health care system & anxiety provided to the people who were falsely told they had the disease.

Explain the quality of screening tests, & the question that must be asked concerning the screening test.

The quality of screening tests is a critical issue. The question must be asked: How good is the screening test at separating populations of people with and without the disease in question?

What were the results, findings, and outcome of James Lind's large-scale experiment with the entire British fleet 47 years after his first experiment?

The results were consistent with the first results and in 1795 the British Navy ordered lemon and lime juice in the sailors' diets.

What is specificity?

The specificity of the test is defined as the ability of the test to identify correctly those who do not have the disease.

Explain the three components of epidemiology.

The three components of epidemiology are: * 1. distribution; * 2. determinants; and * 3. population.

How is the validity of a screening test defined?

The validity of a test is defined as its ability to distinguish between who has a disease and who does not.

Name something that was especially important and noteworthy regarding the Hippocratic Oath?

The value of privacy was especially important and noteworthy.

What were some of the theories concerning the cause of childbed fever?

There were many wrong theories at the time concerning the cause of childbed fever, including: atmospheric toxins and solar and magnetic influences.

What information is needed to calculate the sensitivity and specificity of a test?

To calculate the sensitivity and specificity of a test, we must know who really has the disease & who does not from a source other than the test we are using. Sometimes this source is of another test in use, and sometimes it is the result of a more definitive & often more invasive test.

What kind of information did John Snow investigate to support his theory?

To support his theory of cholera occurring as a result of contaminated water, John Snow carried out what is called shoe leather epidemiology, which in this case involved going house-to-house and writing down who got sick or died from the water and which water company they received water from.

What is a true negative?

True negatives are people without a disease who are correctly called negative

What is a true negative?

True negatives are the number of sick persons diagnosed as not being sick.

What is a true positive?

True positives are people with a disease that are currently called positive.

What are the two components of validity?

Validity has two components: sensitivity and specificity.

Explain the various mortality rates under Semmelweis's direction versus his replacement.

When Semmelweis was in charge of the first obstetrical unit, his efforts helped lower the mortality rate in the first clinic to 2.4%. When Semmelweis was replaced as Director, the rates went up dramatically because the new Director did not implement Semmelweis's theories on handwashing.

Who was a believer in miagmatic theory?

William Farr was a contemporary of John Snow, William Farr was a strong believer in miagmatic theory. William Farr was the Registrar General at the time.

Explain more about parallel testing including testing negative on both tests.

With parallel testing, one must test negative on both tests to not have the disease.

Explain more about serial testing including testing positive on one test versus two tests.

With serial testing, if it is positive on both bests the person is said to have the disease in question. If negative on one test, then the person is said not to have the disease.

Was John Snow's data convincing?

Yes, John Snow's data on cholera was so convincing that William Farr required each district in South London to record which water company supplied water to which house.

Did John Snow's hypothesis go against the leading idea of the time? Explain.

Yes, John Snow's hypothesis went against the leading idea of the time, which was miagmatic theory, which was the idea that the disease was transmitted by a cloud that clung low to the surface of the earth.

Give another example of a disease where we know the cause of the disease, but we do not understand everything about the disease.

Another example of this is the knowledge that streptococcus can lead to rheumatic fever, but we do not know why streptococcus can lead to rheumatic fever.

What were the results of Snow's data collection?

As a result of the data that Snow collected by going house-to-house, Snow found that the water company that moved from a contaminated part of the river to a less contaminated part of the river had dramatically less deaths from cholera.

What is the correlation between sensitivity and specificity?

As sensitivity increases, specificity decreases.

Did the W.H.O. successfully eradicate smallpox? Explain in detail.

By 1980, the W.H.O. eradicated smallpox worldwide. The W.H.O. estimated that approximately 350 million cases of smallpox had been prevented in a 20-year span since its eradication.

What can be learned from John Snow's theory and research?

It can be learned from John Snow's theory and research that it is not always necessary to know pathogenic mechanisms in order to prevent disease.

What is epidemiology?

It is the study of how disease is distributed in populations and the factors that influence or determine this distribution.

Up until 1967, how many people had been affected or killed due to smallpox?

It was estimated that up until 1967, smallpox affected 15 million people, and killed 2 million, and left many blind or disfigured.

What was something that was known about smallpox, and what was sometimes done?

It was known at the time that those who survived infection were subsequently immune from the disease. As a result, some people would purposely infect themselves and others to become immune to the disease, and this often had disastrous results.

When was Semmelweis's theory of handwashing implemented, and what was learned?

It was years later that handwashing was implemented on a regular basis at hospitals around the world. The lessons that can be learned from this story are that supporting evidence is necessary for public and professional acceptance, and that community, and political support is necessary for a policy to be enacted.

How did James Lind become interested in scurvy?

James Lind became especially interested in the treatment of scurvy after he heard that a sailor was cured by eating grasses on an isolated island.

Explain James Lind's experiment.

James Lind conducted an experiment with 12 individuals that had scurvy, and in this experiment the people had the same diet and he tried to keep the conditions similar. Lind divided the 12 people in groups of two, and every group of two people was a test group.

What did James Lind do?

James Lind planned deliberate medical trials to combat scurvy.

Who was James Lind?

James Lind was a Scotish surgeon living in the 1700s that was interested in the treatment of scurvy, a disease that killed thousands of British sailors every year during that time.

Explain James Lind's 6 test groups.

James Lind's 6 test groups included: * 1. One group of two was ordered to have a quart of cider per day; * 2. One group was ordered to have exlixer vitriol. * 3. One group was ordered to have a spoonful of vinegar. * 4. One group was ordered to have sea water. * 5. One group was ordered to have nutmeg; * 6. The last group of two men had two oranges and one lemon.

What did Jenner know about viruses and the biology of disease & what kind of data did he use?

Jenner knew nothing about viruses and the biology of disease. He operated on observational data that provided him with the basis of preventative intervention.

What further observations did Jenner make & what specific conclusion did he reach?

Jenner noticed that when there were outbreaks of smallpox, that the dairy maids that had had cowpox did not develop smallpox. Consequently, Jenner became convinced that cowpox could protect against smallpox, & he decided to test his hypothesis.

How did Jenner test his theory concerning smallpox contraction?

Jenner tested his observation by applying cowpox pus from a milk maid to an 8-year-old boy. A couple of weeks later he applied smallpox pus to the boy and found that the boy did not contract small pox.

What did Edward Jenner theorize & what observations led Jenner to formulate his theory?

Jenner theorized that there was a better way of preventing immunity than deliberate exposure to the disease. Specifically, Jenner observed that dairy maids developed a mild disease similar to smallpox, called cowpox.

Were Jenner's tests successful & explain the results and long-term consequences of his findings.

Jenner's tests regarding vaccinating against smallpox were successful. The results of his findings have saved millions of people from disability and death that would have been caused by smallpox.

What was John Snow's hypothesis?

John Snow hypothesized concerning cholera, and he specifically hypothesized that contaminated drinking water caused cholera.

What is John Snow known as?

John Snow is known as the Father of Epidemiology.

What method did John Snow use to make his hypothesis and determine his findings?

John Snow made his association of contaminated drinking water and cholera based on observation.

Who was John Snow?

John Snow was an epidemiologist in the 1800s who made important observations about cholera, a disease that was a major problem in England at the time.

What was the finding / conclusion of James Lind's experiment that was proven?

Lind's experiment proved a dietary cause of scurvy.

Explain the results of James Lind's experiment.

The best results occurred with the group that was given citrus fruits. One of these individuals was fit for duty in less than a week, and the other individual was doing noticeably better than the other groups.

Talk about the details concerning a high or a low cut off level.

The choice of a high or low cut off level for screening depends on the importance we attach to false positives and false negatives.

Explain what the cut off level means.

The cut off level establishes that the level above the cut off is considered positive and the level below the cut off is considered negative.

What are the effects of these two tests?

The effects of these two tests vary in that with parallel testing there is higher sensitivity but lower specificity. Serial testing on the other hand improves specificity at the cost of lower sensitivity.

How were the first and second obstetrical units at the Vienna General Hospital staffed, and what were the results of the differing duties?

The first obstetrical unit was staffed by physicians and medical students and the second was staffed by midwives and physicians. (In the first clinic, students did autopsies on women who had childbed fever, but the midwives in the second clinic did not do this. The mortality rate in the first clinic was more than double the second clinic.)

What could the gold standard be?

The gold standard could be another test that has been in use, or it could be a more definitive and often more invasive test.

What does the gold standard define?

The gold standard defines the presence of the disease. It is often the best diagnostic assessment available, and also, new screenings are compared to the gold standard.

What is the gold standard regarding screening tests?

The gold standard is an external source of truth regarding the disease status of each individual in the population.

Why is the issue of false positives important?

The issue of false positives are important because all people who are screened positive are brought back for more sophisticated and expensive tests.