FINAL EXAM Material

Question 1

Given a scenario, identify the occurrence of infectious (communicable) diseases : Sporadic

Answer 1

disease occurs infrequently and irregularly

Question 2

Given a scenario, identify the occurrence of infectious (communicable) diseases : Endemic

Answer 2

a health condition that occurs at a steady rate among a population

Question 3

Given a scenario, identify the occurrence of infectious (communicable) diseases : Outbreak

Answer 3

a condition that occurs above endemic levels

Question 4

Given a scenario, identify the occurrence of infectious (communicable) diseases : Epidemic

Answer 4

an outbreak that has spread a larger geographic area, occurrence in a community or region, or causes of an illness (or an outbreak) clearly in excess of expectancy. Relative to “unusual” frequency of the disease.

Question 5

Given a scenario, identify the occurrence of infectious (communicable) diseases: Pandemic

Answer 5

a health condition that has spread globally.

Question 6

Explain how/when epidemics occur

Answer 6

Pending….

Question 7

Describe the four components of the epidemiologic triangle: agent, host, environment, time.

Answer 7

Agents of infectious diseases: microorganisms capable of producing an infectious disease, MUST be present for an infection to occur. (necessary causes), ex: bacterium, virus, protozoan, virulence.
Host: a person or animal that is susceptible to disease will depend on the host’s ability to fight off the infectious agent. Two types of defense mechanisms: innate response macrophage, adoptive response T-lymphocyte and B lymphocyte. Hours to days. Acquired immunity- develops during life time → active immunity : develops in response to an infection or vaccines, & passive : develops after you receive antibodies from someone or somewhere else. Transfer of protective immunity: natural active, transfer of protective immunity: artificial active, long lasting immunity , antibodies produced during a secondary response are bigger, faster, and stronger, active ways.
Environment: the domain in which disease-causing agents may exist, survive and originate, physical environment: weather, temp, humidity, etc…), social environment: behavioral and cultural characteristics of a group of people). Transmission of infectious diseases: the habitat in which infectious agents lives, grows and multiplies (reservoir). Types: environmental reservoirs physical environmental : plant, soil, contaminated food/water. Animal/insect reservoirs: cows, pigs, sheep, rodents, anything that can breathe, Human reservoirs: acute clinical cases: are infected with the disease agent and become ill → because they are ill, their contacts and activities may be limited.
time : natural course of infectious disease, time : susceptible host, subclinical disease stage, Clinical disease stage , stage of recovery.

Question 8

Describe and calculate the following characteristics of infectious diseases agents : Infectivity

Answer 8

ability to cause infection → capability of an agent to enter and multiply in a susceptible host and thus produce infection or disease. ** Active clinical disease (tip of the iceberg) accounts for a relatively small proportion of host’s infections and exposures to disease agents.

Question 9

Describe and calculate the following characteristics of infectious diseases agents : Pathogenicity

Answer 9

ability to cause clinical disease, capacity of an agent to cause active clinical disease in the infected host. Clinical disease: obvious observable or detectable symptoms ( mild → moderate → severe → death).

Question 10

Describe and calculate the following characteristics of infectious diseases agents : Virulence

Answer 10

degree of pathogenicity, severity of the disease after infection occurs.
Formula: total # of cases w/ clinical disease ( subclinical → severe)

Question 11

Define the iceberg concept of infection

Answer 11

Active clinical disease ( the tip of the iceberg) accounts for a relatively small proportion of host’s infectious and exposure to disease agents.

Question 12

Describe the chain of events after exposure to an infectious disease agent

Answer 12

Pending …….

Question 13

Given a scenario, identify the possible type(s) of disease transmission: vertical

Answer 13

from mother to child via mammary glands (milk), placenta (blood) → zika, vagina ( secretion, blood) → HIV

Question 14

Given a scenario, identify the possible type(s) of disease transmission : Horizontal -direct (direct contact, droplets)

Answer 14

transmission of an infection from one individual to another : direct contact ( skin to skin contact, exchange of bodily fluids), ex: animals (dogs, bats), droplets (sneezing, coughing, or even talking).

Question 15

Given a scenario, identify the possible type(s) of disease transmission : Horizontal - indirect (airborne, vector borne, vehicle borne)

Answer 15

contagion between individuals that could be mediated by different means. ex : airborne transmission, vector borne (animate intermediates → typically insects), vehicle borne (inanimate objects) , Airborne transmission: infectious agents are carried by dust or droplet nuclei suspended in air. Vector borne transmission: vector → a living insect or animal involved w/ transmission of the disease agent. Indirect (Vehicle Spread): Vehicle → an inanimate object involved w/ transmission of the disease agent : water, food, soil, fomites. Fomites → objects or materials which are likely to carry infection (door knob, clothing, unsterilized medical equipment, etc). Ex: direct contact, skin/sexual, person to person anthrax, rabies, HIV, syph, E coli, indirect contact giardiasis (fomite), Hep B and C, HIV ( transfusion), rabies ( organs); foodborne : E coli, Hep A, salmonella , Water borne: cholera, : Vector borne, yellow-fever, malaria, Aerosol: common cold, flu, Airbone: anthrax,, trans plancental : HIV, HSV, Perinatal : Hep B, HIV.. etc.

Question 16

Define and describe the types of disease-specific immunity: Natural active

Answer 16

results from an infection by the agent; leads to antibody production in the host → long lasting immunity

Question 17

Define and describe the types of disease-specific immunity: artificial active

Answer 17

vaccine-induced immunity , results from an injection w/ a vaccine that stimulates antibody production in the host → long lasting immunity, antibodies produced during a secondary response are bigger, faster and stronger (active ways)

Question 18

Define and describe the types of disease-specific immunity: Natural passive

Answer 18

similar to vertical transmission during pregnancy – difference here is that the mom transmits antibodies to the baby via placenta. Preformed antibodies are passed to the fetus during pregnancy and during breastfeeding. → Provides immediate, temporary protection to the newborn,

Question 19

Define and describe the types of disease-specific immunity: Artificial passive

Answer 19

Preformed antibodies are given to exposed individuals to confer protection against a disease. Provides immediate, temporary protection. Ex: person bit by rabid dog → w/ antibodies of someone who is immune to rabies infection.

Question 20

Differentiate between the different types of carriers: Asymptomatic (healthy)

Answer 20

never develop an illness but can transmit their infection. Ex: of every 100 individuals infected w/ the the poliomyelitis virus.

Question 21

Differentiate between the different types of carriers : Incubatory

Answer 21

are people going to become ill but begin transmitting their infection before their symptoms start. Ex: a person infected w/ measles begins to shed the virus in nasal and throat secretions a day or two b4 any cold symptoms or rush are noticeable.

Question 22

Differentiate between the different types of carriers: Convalescent

Answer 22

ppl who continue to be infectious after their recovery from illness. Ex: this happens w/ many diseases, salmonella patients may excrete the bacteria in feces for several weeks, and rarely even for a yr or more.

Question 23

Differentiate between the different types of carriers: Chronic

Answer 23

ppl who continue to harbor infections from a year or longer after their recovery. Ex: the chronic carrier state is not uncommon following Hep B infection, whether or not the person became ill, and may be life long. superspreaders : asymptomatic carriers: someone who is responsible for infecting many people. 80/20: in any given outbreak : 20 % of the individuals w/in any given pop are thought to contribute at least 80% to the transmission of potential pathogens. ex : typhoid mary.

Question 24

Differentiate between generation time and incubation period

Answer 24

Generation-time: time interval between exposure to an infectious agent and maximal infectivity of the host. Can precede the development of active symptoms , useful for describing the spread of infectious agents that have lrg proportions of subclinical cases. Applies to both in apparent and apparent cases of disease , generation time and incubation period may or may not be equivalent.
Incubation period: time interval between exposure to an infectious agent and the appearance of the first sign and symptoms of disease infection.

Question 25

Given a scenario, identify the possibly type of epidemic (epi) curves: Common source (point, continuous, or intermittent)

Answer 25

Point source: persons are exposed to the same common source over a brief period of time (e.g - single meal or event), majority of cases occur w/in one incubation period. Continuous common source: exposure is not confirmed to one pt in time (prolonged over days, weeks or yrs), last more than one incubation period. Intermittent source: (random, but source is known, can’t relate to incubation period; similar to continuous but exposure is intermittent, multiple peaks, no relation to the incubation period (e.g contaminated food product sold over period of time). Randomness to people being exposed peaks.

Question 26

Given a scenario, identify the possibly type of epidemic (epi) curves: Propagated source

Answer 26

does not have common source but instead is caused by spread of infectious agent from one susceptible person to another; transmission may occur directly or via an intermediate host, multiple peaks separated by one incubation period.

Question 27

Provide formula, calculate and interpret the following measures of disease outbreaks: Attack rate

Answer 27

the proportion of a group that experiences the outcome understudy over a given period of time ; reserved for infectious disease outbreaks : acute infectious disease outbreaks (food borne illness, other acute infectious diseases), acute exposures of lrg groups to toxic agents. Eq: attack rate = ill / (ill + well) *100 during a time period.

Question 28

Provide formula, calculate and interpret the following measures of disease outbreaks: Secondary attack rate

Answer 28

an index of the spread of disease in a family, household dwelling unit, dormitory or similar circumscribed group, a measure of infectivity, eq: # of new cases in group - initial case(s)/ # of susceptible persons in the group initial cases.

Question 29

Provide formula, calculate and interpret the following measures of disease outbreaks: Case fatality rate (CFR)

Answer 29

proportion formed by the # of deaths caused by a disease by disease among those who have the disease during a time interval. Formula: # of deaths due to disease “X” / # of cases of disease “ X” of a particular disease * 100 during the time period., index of the virulence of a particular disease w/in a specific population.

Question 30

Provide formula, calculate and interpret the following measures of disease outbreaks: Basic reproductive rate (Ro)

Answer 30

a measure of the # of infections produced on avg by an infection individual in the early stages of an epidemic when virtually all contacts are susceptible * superspreaders infect more than avg , can be used as a measure of the transmissibility (contagiousness) , Use avg Ro to determine the contagiousness of a disease.

Question 31

Given attack rate data, identify the most probable vehicle for infection.

Answer 31

N/A

Question 32

Differentiate between the different types of cases: Index case

Answer 32

case that first comes to attention of public health authorities

Question 33

Differentiate between the different types of cases: Coprimaries

Answer 33

cases related so closely in time that they are considered to belong to same generation of cases

Question 34

Differentiate between the different types of cases: Initial case

Answer 34

index case + coprimaries.

Question 35

Differentiate between the different types of cases: Secondary case

Answer 35

person(s) who become ill after becoming infected from contact w/ a primary case.

Question 36

Explain how herd immunity confers protection to the population.

Answer 36

immunity of a population, group, or community against an infectious disease when a lrg proportion of individuals are immune either through vaccinations or prior infection. The majority of the population must be immune (ie: vaccinated or recovered from illness). Goal = Ro to drop below 1.0 ( # of cases is decreasing)

Question 37

Describe the steps in investigating an infectious disease outbreak.

Answer 37

1) Establish the existence of an outbreak: is this a group of related cases that are part of an outbreak or a single sporadic case? Even if the current # or reported cases exceeds the expected #, the excess may not necessarily indicate an outbreak. Ex: was there a change in local reporting procedures? Was there a change in the case def? Were there improvements in diagnostic procedures? Was there increased interest b/c of local or national awareness. 2) Verify the diagnosis: review the clinical findings and lab results, visit one or more patients w/ the disease to ask questions abt exposures, contacts, etc. 3) Construct a working case definition: a standard set of criteria for deciding whether an individual should be classified as having the health conditions of interest. Must include – clinical criteria; setting of the outbreak investigation ( place, person, time), Should not include : exposure risk factor you are evaluating : may not be known. 4) Find Cases systematically and record information: passive surveillance: sending letters describing the situation and asking for reports of similar cases. Active surveillance: telephoning or visiting the facilities to collect information on any additional causes. Data collection should include: ID infor ( name, address, phone number), demographic info ( age, sex, race, occupation), clinical info (signs, symptoms, date of onset symptoms), risk factor info ( exposure to food or water sources, reporter info : physician clinic, hospital, lab. 5) Perform descriptive epide: outbreak os characterized by person, place, time. Person: by sex, race + ethnicity + age. Place: create spot maps e.g: by state by country, by neighborhood, TIME: plot the epi curve, calculate incubation period. 6) Develop hypothesis: hypothesis could address: source of the agent - the mode ( and vehicle or vectors) of transmission, exposures that caused the disease, must be testable. 7) Evaluate hypothesis epidemiologically comparing the hypothesis w/ the established fact: used when clinical. Lab, environmental, and/or epidi evidence so obviously supports the hypothesis that formal testing is unnecessary, or using analytic epidi to quantity: relationships and assess the role of chance : – cohort studies = relative risk + attack rates, cause-control studies – odds ratio. 8) reconsider, refine, and re-evaluate hypothesis: consider conserving a meeting of the case -patients to look for common links or using their homes to look at the products on their shelves, consider new vehicles or modes of transmission, use a more specific control group. 9) Implement control and prevention measures: if appropriate control measures are known and available, they should be initiated even before an epidemiological investigation is launched, control measures are usually directed towards one or more segments in the chain of transmission/ agent, source, mode of transmission, portal of entry, host) that are susceptible to intervention. 10) communicate findings : situation report/ summary, an oral briefing for local authorities.

Question 38

Given a line listing, determine whether each patient should be classified as a case according to the case definition.

Answer 38

N/A

Question 39

Define the term screening and explain how screening is different from diagnosis.

Answer 39

Screening: the presumptive ID of unrecognized diseases or detected by the application of tests, examinations or other procedures that can be applied rapidly. Positive screening results are followed by diagnostic tests to confirm actual disease. Tests: to detect potential disease indicators, target lrg # of asymptomatic individuals, simple and cheap, results indicate suspicion of disease. Diagnosis: to establish the presence/ absence of disease, target single symptomatic individuals of asymptomatic individuals w/ positive screening tests, maybe invasive and costly, results provide define diagnosis.

Question 40

Describe appropriate situations for screening tests and programs and give examples of when we should not screen for diseases.

Answer 40

Mass population screening = screen the entire population regardless of risk status. Ex: measure temp @ airport to ID people who may be harboring a deadly infectious disease such as ebola. Secletive (targeted) screening: screen specific froups who are high risk disease ex: HIV screeing for sex workers or IV drug users. Social: the health problem should be important for the individual and the community. Diagnostic follow up and interventions should be available to all who require them. There should be a favorable cost-benefit ratio, public acceptance must be high. Scientific: natural history of the condition should be adequately understood → knowledge permits id of early stages of disease and appropriate biologic markers of progression. Acknowledge base exists for the efficacy of prevention and the occurrence of side effects. Prevalence of the disease or condition is high. Ethical: the program can alter the natural history of the condition in a significant way and diagnosis of the condition as well as acceptable effective methods of prevention are available.

Question 41

Describe the five characteristics of a good screening test.

Answer 41

Simple: easy to learn + perform : rapid : quick to administer inexpensive : favorable cost-benefit analysis/ ratio safe : no harm to participants Acceptable : target population will use the test.

Question 42

Describe the interrelationship between reliability (precision) and validity (accuracy) in the evaluation of screening tests.

Answer 42

Reliability: the ability of a measuring instrument to give consistent results on repeated trials. Validity ( accuracy): the ability of a measuring instrument to give a true measure. Interrelationship: it's possible for a measure to be highly reliable but in valid. It's not possible for a measure to be valid but unreliable.

Question 43

Provide formula, calculate, and interpret the following measures of validity of screening tests if given a 2x2 table for screening : Sensitivity

Answer 43

Sensitivity : proportion of ppl who test positive among all those who actually have the disease: the # of true positives (a) determined by the sum of the false positives and the true positives (a+c). Formula: (%) = a/a+c *100 , interpretation: percentage of the positives: % sensitivity = __ % of ppl who have the target disease will test positive.

Question 44

Provide formula, calculate, and interpret the following measures of validity of screening tests if given a 2x2 table for screening : Specificity

Answer 44

proportion of ppl who test negative among all those who do not have that disease: the # of true negatives (d) divided by the sum of the true negatives (b+d). formula : (%) = d/(b+d) *100. Interpretation: percentage of true negatives : __% specificity = __% of ppl who do not have the target disease will test negative.

Question 45

Provide formula, calculate, and interpret the following measures of validity of screening tests if given a 2x2 table for screening : Predictive (+)

Answer 45

probability that following a positive test value that individual will truly have that specific disease, # of true positives (a) / sum of true positives + false positives (a+b). Formula: (%) = a / (a+b) *100

Question 46

Provide formula, calculate, and interpret the following measures of validity of screening tests if given a 2x2 table for screening: Predictive value (-)

Answer 46

probability that following a negative test result, that individual will truly not have that specific disease : the # of the negatives (d) / sum of false positives and negatives (c+d), formula: d / (c+d) *100

Question 47

Provide formula, calculate, and interpret the following measures of validity of screening tests if given a 2x2 table for screening: Accuracy of screening test

Answer 47

the degree of agreement between the test results and the gold standard: sum of the true positives + true negatives (a+d)/ (a+b+c+d) *100. Formula: (a+d) / ( a+b+c+d) *100

Question 48

Provide formula, calculate, and interpret the following measures of validity of screening tests if given a 2x2 table for screening: Prevalence

Answer 48

the # of existing cases of a disease or health condition a population @ a point or during a period of time. Formula : (a+c) / (a+b+c+d) *100.

Question 49

Explain how the predictive value of a screening can vary according to the prevalence of disease.

Answer 49

When the prevalence of a disease falls, the predictive value (+) falls, and the predictive value (-) rises. Sensitivity and specificity are affected by the prevalence of a disease. Specificity : the ability of the test to ID only non-diseased individuals who actually do not have the disease

Question 50

Describe the interrelationship between specificity and sensitivity, and explain the procedures to improve the specificity or sensitivity of a screening test.

Answer 50

To improve sensitivity, the cut point used to classify individuals as diseased should be moved towards the range of the normal (A ← C) , almost all individuals that have the disease will be screened as positive. Sensitivity: the ability of the test to id only disease individuals who actually have the disease . Improvement?; retain screeners – reduces the amount of misclassification in test that require human assessment, recalibrate screening instruments – reduces the amt of imprecision, utilize a different test, utilize more than one test.

Question 51

Describe the sources of bias in screening

Answer 51

Lead time bias: the perception that the screen-detected case has longer survival b/c the disease was identified early. Length bias: Disease identified through screening has slower, less aggressive course and therefore better prognosis: → particularly relevant to cancer screening. Selection bias: motivated participants have a different probability of disease than do those who refuse to participate.

Question 52

Define the term environmental epidemiology

Answer 52

Study of disease and health conditions (occuring in the population) that are linked to environmental factors. Environmental exposures – outside the control of the exposed individual. Study designs: descriptive (cross-sectional studies) : helpful for setting priorities, Id hazards , formulating hypotheses for new occupational risks, analustic (ecologic, cohort, case-control), used to show exposure-effect relationships, effects of low levels exposures.

Question 53

Give examples of recent environmental catastrophes that are associated with human health effects

Answer 53

cancer , lung disease, infertility, reproductive impacts (congenital malformations, low birth weight) , infectious diseases (including malaria), neurologic diseases, dermatologic problems.

Question 54

Define the healthy worker effect and explain its impact on occupational morbidity and mortality.

Answer 54

Observation that the employed population tend to have a lower mortality experience than the general population. Healthy worker effect may reduce the measure of effect for an exposure that increases morbidity or mortality.

Question 55

Discuss the advantages and disadvantages of using each of the following end points for occupational exposures: Morbidity

Answer 55

self reports of symptoms , results of clinical examinations

Question 56

Discuss the advantages and disadvantages of using each of the following end points for occupational exposures: Mortality

Answer 56

comparison of mortality rates of exposed workers with non exposed workers in the same industry

Question 57

Define hazard surveillance and explain its purpose

Answer 57

Characterized of known chemical, physical and biological agents in the workplace. (**most effective** elimination → physically remove the hazard; substitution → replace the hazard ; engineering control → isolate ppl from the hazard, admin controls → change the way ppl work. ; ** least effective**PPE → protect the worker w/ personal protective equipment.

Question 58

Discuss the concept of a sentinel health event.

Answer 58

Case of unnecessary disease, unnecessary disability, or ultimately death whose occurrence is a warning signal that the quality of preventative or medical care may need to be improved, ( form of secondary prevention).

Question 59

Describe the methodological difficulties associated with research on environmental health effects.

Answer 59

Hazard Waste sites: Ex: love canal, NY (1973), residents experienced high rate of birth defects, neurological disease and cancer. Waste sites include a complex mixture of substances, studies may not adequately control for confounding factors, long-term effects of exposure are difficult to measure, effects of low-level exposures are difficult to demonstrate, and small study samples. Air pollution: studies have shown a correlation btwn increase in daily mortality and increased air pollution. ex : passive (second hand) smoking; causes 3000 lung cancer deaths annually among nonsmokers is associated with children’s bronchitis, pneumonia , and asthma. Methodological difficulties : small increase in risk of death from positive smoking are difficult to demonstrate, short-term vs. long-term exposure, exposure to cig smoke : from many sources, long latency period between exposure to cig smoke and onset of disease. Nuclear Facilities: include weapons production plants, tests, sites and nuclear power plants → studies of living in close proximity to nuclear installations have shown conflicting results regarding cancer rates. Drinking water: sources of underground water contamination include: industrial facilities, new human habitation, run-off from growing urbanized areas, pathogenic microorganisms, – pesticides, radio activity, etc. much is still unknown about the effects of chemical pollutants in water.

Question 60

Given relevant count data, calculate and interpret the prevalence or incidence of a disease using the appropriate formula.

Answer 60

Prevalence = the # of existing cases of a disease or health condition in a population at pt or during a period of time. Eq = prevalence → of persons ill / total # in the group @ a time pt * multiplier Incidence = the # of new cases of a disease that develop in a pop @ risk over a specified time period. Eq : # of new cases during a time period / total population @ risk during the same time period * multiplier.