epidemiology prep for exam 1

john snow (1813-1858)

"Father of Epidemiology", studied the London Cholera epidemics of 1848 & 1854, suspected it was from the water, as most cases were found close to the Broad Street pump

father of medicine

Hippocrates, a Greek physician based medical practice on observation and study of the human body -believed illness had a physical and rational explanation essay on airs, waters, and places environmental and host factors influence development of disease

This historic character observed that childbed fever mortality was more common among women treated by physicians and medical students compared with women treated by midwives. Based on his observations, he implemented a hand wash policy that resulted in a decrease in mortality. Name the character that we are talking about.

Ignaz Semmelweis

Over the past century, a marked decline in the mortality rates of many infectious diseases has been observed. Which of the following is the most likely reason for the observed decline in mortality rates from common infectious diseases?

Improvement in social conditions

For a disease such as seasonal influenza, which is less fatal and of short duration?

Incidence rates will be much higher than mortality rates.

A patient is weighed in the hospital by a nurse, and she is told she weighs 170 pounds. The next morning she weighs herself at home, and her weight is 168 pounds. Assuming that both scales were calibrated and the patient was measured under the same circumstances (no shoes, light clothing). What can explain the difference in weight?

Intrasubject variability

What are similarities between Semmelweis, Snow, and Jenner?

-All utilized observational data -All served a role in developing policies/practices

five objectives of epidemiology

1. To identify the etiology or cause of a condition 2. To determine the extent of a condition 3. To study the progression of a condition 4. To evaluate preventive and therapeutic measures for a condition 5. To develop public health policy

outbreak investigations

1. establish existence of an outbreak 2. prepare for fieldwork 3.define and identify cases 4.use descriptive epidemiology 5.develop hypotheses 6.evaluate the hypotheses 7.refine the hypotheses 8. implement control and prevention 9.communicate findings 10.maintain surveillnce

PPV is effected by two factors

1. prevalence- higher prevalence equals a higher PPV 2. specificity- if prevalence is low, increasing specificity will improve ppv

An epidemiologist decides to investigate the incidence of diabetes in a population of 300 older adults who live in a nursing home. She visits the nursing home in January 1, 2017 and later in December 31 of the same year. She looks into the records of these patients and learns that in her first visit, 25 patients had diabetes and 35 in her second visit. What number should be in the numerator for her calculation of incidence?

10 These 10 people represent the new cases of diabetes, because at the beginning there were already 25 diabetics. 300 represents the total population, and 275 represents the population at risk of diabetes at the beginning of the study.

What is the age-specific mortality rate from disease X in City B for age younger than 65? Use the following table to answer the question.Number of Residents and Deaths From Disease X by Age Group in City A and City B

10 deaths/1,000 people The age-specific mortality rate of City B for age younger than 65 equals the number of deaths for age younger than 65 divided by the number of individuals at risk for age younger than 65. There are 60 deaths for age younger than 65 in City A, and its population is 6,000 people for age younger than 65. The age-specific mortality rate of City B for age younger than 65 is 10 deaths/1,000 people.

What is the incidence rate from influenza in the 2016 season in the young age group at Minas Tirith? Use the following table to answer the question.Number of Residents, Diagnosed Cases, and Deaths From Influenza by Age

150/1000 people

There was a food poisoning outbreak on April 1, 2018, at the City Z Food Safety Conference. There were 1,000 people registered for the conference with luncheon, 100 volunteers to host attendees, and 50 people who served the luncheon during the conference. Except for 50 people who served the food, all of the participants and volunteers ate the food from the luncheon at the conference on April 1, 2018. After an initial outbreak of food poisoning is reported, an epidemiologist sends surveys to all people at risk to investigate the cause. However, only 900 people among those at risk answered the survey. After analysis of 900 survey results, the epidemiologist concludes that the most suspected foods in the outbreak are pepperoni pizza and meatball spaghetti. What is the overall attack rate for those who ate meatball spaghetti? Use the following table to answer the question. Summary of Survey Responses

23% soultion To calculate the food-specific attack rate, we need to define how many people are exposed to the specific food and how many people develop the symptoms in the case definition. In this question, we are asking about "overall" attack rate in those people who ate meatball spaghetti, so we have to add "meatball spaghetti only" and "both pepperoni pizza and meatball spaghetti" to get the overall rate. Which is 525 (375 plus 150), who are at risk of exposure, and 119 (62 plus 57), who developed the symptoms, corresponding to 23% of attack rate.

In 2016 there were 7,467 million people in the world. According to the World Health Organization, in the same year there were 56.9 million deaths worldwide; of those, 15.2 million were due to ischemic heart disease or stroke. What was the proportionate mortality of those two causes combined for that year?

26.7% The proportionate mortality represents the percentage of all deaths that are due to a specific cause (in this example, two causes combined). We calculate it using the following procedure: 56.9 million if the total number of deaths = 100% deaths. There were 15.2 million deaths due to ischemic heart disease or stroke; therefore 15.2 million represents 26.7% of all deaths. Another way to express this number is 26.7% of all deaths were due to ischemic heart disease or stroke: (15.2 x 100 )/56.9 = 26.7%

An epidemiologist decides to investigate the incidence of diabetes in a population of 300 older adults who live in a nursing home. She visits the nursing home in January 1, 2017 and later in December 31 of the same year. She looks into the records of these patients and learns that in her first visit, 25 patients had diabetes and 35 in her second visit. What number should be included in the denominator for her calculation of incidence?

275 Because 25 patients already had diabetes at the beginning of her study, only 275 were at risk of diabetes. The denominator for calculating incidence should be the population at risk of getting the disease; therefore 275 is the right answer.

According to the Centers of Disease Control and Prevention (CDC), during the Ebola outbreak of 2014 in West Africa, there were a total of 14,124 Ebola cases in Sierra Leone and 3,956 deaths due to Ebola. What was the case fatality rate in that country?

28% 3,956 deaths represent 28% of the total number of cases of Ebola. This proportion is known as the case-fatality rate.

A physical examination, digital rectal exam, was used to screen for prostate cancer in 290 men with biopsy-proven prostate cancer and in 516 age- and race-matched control men, all of whom showed no evidence of cancer at biopsy. The results of the physical examination were positive in 136 cases and in 165 control men. What is the sensitivity of the physical examination?

47%

Two infectious disease epidemiologists want to investigate a new laboratory test that identifies tuberculosis (TB) infections. Dr. Merritt uses the standard test, which has a sensitivity of 80% and a specificity of 90%. Dr. Foundry uses the new laboratory test, which is 90% sensitive and 99% specific. In City A, it is known that 100 of 1,000 people have TB infections. What is the positive predictive value of the standard test in City A?

47% Positive predictive value is the proportion of those who test positive who do have the disease or the probability that a person identified as diseased by the test will be a diseased person (case) in the population. Let us say there are 10,000 people in City A; 100 of 1,000 people actually have TB infection in City A which is 1,000 individuals. Therefore we have 1,000 cases and 9,000 noncases in City A (hypothetically). The number of people who identified as test positive from cases is 800. Among 1,000 people who actually have TB, 80% of people will be identified as test positive (sensitivity). The number of people who identified as test positive from noncases is 900. Among 9,000 people who actually have TB, 90% of people will be identified as test negative (specificity) and 10% of people will be identified as test positive. Among 1,700 people who identified as test positive, there are 800 people who actually have the disease. Therefore positive predictive value equals 800 divided by 1,700 (equals 0.47).

What is the mortality from influenza during the 2016 season in the old age group at Minas Tirith? Use the following table to answer the question.Number of Residents, Diagnosed Cases, and Deaths From Influenza by Age

50 deaths/1,000 people Mortality rate equals the number of deaths divided by the number of people at risk. There are 500 deaths in the young age group, and its population is 10,000 people. The mortality rate is 50 deaths/1,000 people. 300 deaths is not correct; 300 deaths is the number of deaths from influenza in the young age group. 500 deaths is not correct; 500 deaths is the number of deaths from influenza in the young age group. 150 deaths/1,000 people is not correct; 150 deaths/1,000 people is the incidence rate from influenza in the young age group with the wrong unit (incidence rate unit should be cases/people). 100 deaths/1,000 people is not correct; 100 deaths/1,000 people is the incidence rate from influenza in the old age group with the wrong unit (incidence rate unit should be cases/people).

A 60-year-old patient, who is an epidemiologist, was tested for Raven disease; his test came back positive. However, he is curious about the sensitivity of the test. Using this table, calculate the sensitivity of the test

70%

A 60-year-old patient was tested for Raven disease; his test came back negative. However, he feels the test might be wrong and wants to know what is the probability of not having Raven disease given that his test came back negative. Using this table, answer to the following question: what proportion of the patients who tested negative are truly disease free?

96%

A diagnostic test with a very high sensitivity but very low specificity has the following problem:

It will label a big proportion of healthy people as sick (false-positives)

edward jenner (1749-1823)

Developed a vaccination for smallpox in 1796

Pandemic

Disease that occurs over a wide geographic area and affects a very high proportion of the population.

if proportionate mortality = x/y * 100%, then x =

Number of deaths from a disease in a year

There was a food poisoning outbreak on April 1, 2018, at the City Z Food Safety Conference. There were 1,000 people registered for the conference with luncheon, 100 volunteers to host attendees, and 50 people who served the luncheon during the conference. Except for 50 people who served the food, all of the participants and volunteers ate the food from the luncheon at the conference on April 1, 2018. After an initial outbreak of food poisoning is reported, an epidemiologist sends surveys to all people at risk to investigate the cause. However, only 900 people among those at risk answer the survey. After analysis of 900 survey results, the epidemiologist concludes that the most suspected foods in the outbreak are pepperoni pizza and meatball spaghetti. What is the most suspected food for food poisoning after cross-tabulation? Use the following table to answer the question.Summary of Survey Responses

Pepperoni pizza only

surveillance in low income countries

difficulty in reaching geographically remote areas difficult to maintain communication between policymakers and people in the field defining cases may be difficult due to a lack of resources -equipment -clinical spaces

Thanks to the contributions of Edward Jenner, the following disease was eradicated later by efforts organized by D.A. Henderson:

Smallpox

Which of the following is an example of tertiary prevention?

Surgical amputation of an extremity with osteosarcoma (bone cancer)

What is the most accurate definition of the incubation period (of an infectious disease)?

The interval from receipt of infection to the time of onset of clinical illness (the onset of recognizable symptoms)

Which of the following statements about specificity is the most accurate?

The probability that a person without the disease (noncase) in the population tested will be identified as nondiseased by the test.

positive predictive value PPV

The probability the client has the disease if the test result is positive TP(TP+FP)

herd immunity

The resistance of a group to an attack by a disease to which a large proportion of the members of the group are immune conditions -disease must be restricted to a single host species -transmission must be direct from one member to another -infectious and vaccination must induce solid immunity

Epidemiology

The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems.

vector

disease caused by a parasite vector isn't always included in the triad, but explains the transmission for certain diseases -mosquitos -tick -fleas

Gold standard test

a diagnostic test that is considered to be the most accurate and best available under a particular condition or set of conditions invasive

Host

a human who is susceptible to contracting the disease host characteristics: -age -sex -genetics -family history -occupation -health behaviors -immune status

active surveillance

a projected staff make periodic visits to health care facilities or communities to identify new cases involves interviews with physicians and patients pros: much more accurate than passive surveillance. can identify cases that may have went unreported or unidentified cons: more expensive. more resources are needed to develop a surveillance plan, and hire workers time consuming

screening test

a screening test is done to attempt and quickly identify who may have a disease and who may not screening tests are often cheaper, less invasive, and quicker ways to diagnose people less accurate than the gold standard test biopsy includes: physical exam laboratory tests imaging procedures genetic tests

validity

accuracy or correctness the ability of a test to distinguish between people who have a disease and people who do not sensitivity specificity

primary

action taken to prevent the development of a disease in a person who does not have the disease types of prevention vaccination, mask wearing

In the student's health clinic of a certain university, 140 cases of foot-hand-mouth disease were identified among the undergraduate students. This viral infection is usually mild, and none of the students got any complication. Because it is rare to observe this condition in people older than 10 years, the university reported their findings to the city's health department. Three officers were sent to the university to interview and examine all the infected students and their contacts. By sending the three officers, what type of surveillance was implemented by the city health department in response to the university's report?

active

__________________________________ occurs when project staff are hired to make periodic field visits to health care facilities in order to identify new cases of a disease or diseases or deaths from the disease that have occurred (case findings).

active surveillance

A disease-specific mortality rate and ____________________________ are likely to have the same denominator.

all-cause mortality

endemic

an endemic has a habitual presence within a geographic area

passive surveillance

available data on reportable diseases are used reportable diseases and conditions are required by law to be reported to local health departments. the list of reportable conditions can vary from state to state pros: inexpensive initially easy to develop cons: underreporting data is not created for research purposes. therefore it can be difficult

proportionate mortality

changes in proportionate mortality over time may be due to changes in mortality in other diseases -getting worse -getting better -cannot tell us the risk of dying from a disease

surveillance of health behaviors

continual surveillance of health behaviors helps monitor behavioral trends -monitor trends -target resources common systems -BRFSS -YRBS -NHANES -NHIS

john graunt (1620-1674)

developed early statistical and census methods -founded science of demography published bills of mortality in 1662 -first statistically based estimation of the population of london -quantified patterns of births, death, and disease occurrence

One of the 5 objectives of epidemiology is: to identify the ______________ of a disease and its relevant risk factors.

etiology or cause

age specific

example

cause-specific mortality rate

example

sex specific

example

One of the 5 objectives of epidemiology is: to determine the ________________________________ found in the community.

extent of disease

environment

extrinsic factors that affect the opportunity for exposure environmental factors -temperature -humidity -food/milk -neighborhood -crowding

case-fatality rate

fatality is a proportion of people who have a condition

Ignaz Simmelweis

hand-washing to prevent childbed fever, washed with chloride and lime to prevent the spreading of disease

epidemiologic triad

host, agent, environment, vector

secondary

identify people who already have the disease at an early stage mammogram types of prevention diagnostic testing quarantine

Suppose that the incidence of all types of cancer remains constant in a given country. However, thanks to new treatments, the survival of cancer patients increases. What do you expect to happen to the prevalence of cancer in that country?

increase

attack rate

number of people at risk in whom a certain illness develops/total number of people at risk person time place

if the all-cause annual mortality rate = x/y ⋅100,000then: y =

number of persons in the population at midyear

epidemic

occurrence in a community or region of an illness in excess of normal expectancy usually occurring in higher than normal expected rates over a period of time

agent

originally defined as an infectious microorganism or pathogen -chemical -physical -nutritional

______________________________ uses available data on reportable diseases or in which disease reporting is mandated or requested by the government or the local health authority with the responsibility falling on the health care provider (or lab) or district health officer.

passive surveillance

Mr. Patient tested positive for disease X. He went to see Dr. Gordis and asked him what was the probability of truly being sick given the results of the test. To answer that question, Dr. Gordis must know what about the test?

positive predictive value

tertiary

prevention or limitation of complications of the disease in question surgery types of prevention hospitalization ventilator

A disease-specific mortality rate and ____________________________ are likely to have the same numerator.

proportionate mortality

prevalence is decreased by

refer to the picture

prevalence is increased by

refer to the picture

passive surveillance

sending letter to clinicians and asking for reports of similar cases

active surveillance

telephoning or visiting clinical facilities to collect information

specificity

the ability of a screening test to correctly identify people who do not have the disease TN/( TN + FP)

sensitivity

the ability of a screening test to correctly identify people who have the disease TP/(TP+ FN)

why is it important to identify people with the disease?

the clinical issue is patient care there are 2 public health issues 1.secondary prevention 2.etiologic research towards primary prevention

incidence rate

the number of new cases of a disease that occur during a specified period of time in a population at risk for developing disease

surveillance

the ongoing systematic collection, analysis, and interpretation of health data essential to the planning, implementation, and evaluation of public health practice closely integrated with the timely dissemination of these data to those who need to know provides decisionmakers guidance for developing and implementing the best strategies two types passive and active

negative predictive value NPV

the probability the client does not have the disease if the test results are negative TN/(TN+ FN)

prevalence

the proportion of people in a population affected by a disease -how many are affected at this point in time = point prevalence -how many are affected over a period of time = period prevalence prevalence is a measure of disease burden

Morbidity

the state of being diseased or unhealthy

morbidity

the state of being diseased or unhealthy

mortality

the state of being subjected to death

If the all cause annual mortality rate =x/y ⋅100,000 then: x =

total number of deaths from all causes in 1 year