Epidemiology

Question 1

Fill in the blanks: ‘Epidemiology is the study of the __________ and ___________ of disease frequency in human/animal populations and the application of this study to control health problems.’

Answer 1

(Distribution and determinants)

Question 2

What are determinants of disease?

Answer 2

(Factors that cause some individuals to acquire disease and/or factors that prevent some individuals from getting disease → aka EXPOSURES)

Question 3

What is the term for a testable statement that tries to explain a set of observations and can be tentatively rejected/not rejected through scientific research?

Answer 3

(Hypothesis)

Question 4

What is the difference in the use/purpose of descriptive and scientific/analytical studies?

Answer 4

(Descriptive - describe patterns of disease; scientific - search for disease causes and prevention)

Question 5

What is the limitation of descriptive epidemiology?

Answer 5

(It cannot identify the causes of disease)

Question 6

What is the term for the resistance to spread of contagious disease within a population if a high proportion are immune?

Answer 6

(Herd immunity)

Question 7

How is herd immunity accomplished? Three answers.

Answer 7

(Natural exposure, controlled exposure, or vaccination)

Question 8

The key to excluding pathogens is to remember what characteristic about them?

Answer 8

(How they spread)

Question 9

How long is the suggested quarantine or isolation period?

Answer 9

(45 days (I’m adding this because it’s intuitive, for isolation with a known disease, the isolation period will depend on the disease present so 45 days is likely a catch all but not perfect for every disease)

Question 10

When vaccines are non-existent or poorly effective for a certain disease, what becomes your best option?

Answer 10

(Premunization aka controlled exposure)

Question 11

Long term stress increases or decreases your resistance to bacterial, parasitic, and viral pathogens. Give an answer for each category.

Answer 11

(Bacterial - increases; parasitic - increases; viral - decreases)

Question 12

How is scrapie controlled in sheep populations?

Answer 12

(You destroy genetically susceptible sheep in affected flocks (so bloodline related sheep of scrapie positive animals) or those possessing scrapie-susceptible PrP alleles; this is a good example of using genetics to control disease)

Question 13

How is scrapie controlled in goat populations?

Answer 13

(Goats that are exposed to scrapie positive sheep are destroyed)

Question 14

(T/F) The inclusion of coccidiostats in poultry feed are meant to rid the population of coccidian infections entirely.

Answer 14

(F, they are meant to limit coccidial replication and allow time for immunity to develop, then you can pull the coccidiostats prior to going to market and the birds will not get sick)

Question 15

Besides treating the sickness associated with leptospirosis in dogs, what is the other purpose of leptospirosis treatment?

Answer 15

(Eliminates shedding to reduce the likelihood of spread to naive animals and people)

Question 16

Water chlorination and/or access to clean drinking water is important for the prevention of what parasite in backyard chicken flocks?

Answer 16

(Trichomoniasis)

Question 17

What nutritional control of disease is utilized in shelter dogs to help control diarrhea?

Answer 17

(The administration of pre and probiotics at the time of admission)

Question 18

What nutritional control of disease is utilized in backyard chickens to prevent trichomoniasis?

Answer 18

(Providing access to clean and/or chlorinated water as pigeons carrying Trichomonas gallinae contaminate water supplies)

Question 19

Give two examples of using immunity to control disease spread.

Answer 19

(1. FMD ring vaccinations prevent spread beyond the infected zone due to host resistance; 2. rabies vaccination of urban domestic animals creates a buffer against sylvatic rabies crossing over to urban areas, 3. providing colostrum and pre/post weaning IBR/BVD/PI-3/BRSV vaccinations to reduce susceptibility to 2ndry M. haemolytica infections)

Question 20

What is the first step in containing a disease outbreak?

Answer 20

(Inform the owner of your concerns; this should be done before contacting authorities)

Question 21

What is the first step in eliminating infectious agents from the environment (truck bed, housing, etc.)?

Answer 21

(Removal of gross organic material)

Question 22

Does low or high stress increase an animals’ susceptibility to bacterial and parasitic pathogens?

Answer 22

(Low stress)

Question 23

Does low or high stress increase an animals’ susceptibility to viral pathogens?

Answer 23

(High stress)

Question 24

Although intense genetic selection produces uniformity in phenotypes especially in relation to desirable production characteristics, it also reduces survivability by altering what other characteristic of the animals?

Answer 24

(Disease resistance → decreases it)

Question 25

What is the difference between a fixed and dynamic population?

Answer 25

(Fixed populations are associated with permanent membership to that population i.e. veterans of the vietnam war; dynamic populations are associated with transient membership to that population i.e. graduate students)

Question 26

Why is it important to distinguish between your study population being fixed versus dynamic?

Answer 26

(It will guide you to the appropriate measures of disease frequency and study designs)

Question 27

What is the term for the measurement of disease in which the numerator is a subset of the denominator?

Answer 27

(Proportion)

Question 28

What is the key difference between a ratio and a proportion?

Answer 28

(In a ratio, the numbers used do not need to be related to each other whereas with a proportion, the numbers must be related, specifically the numerator is a subset of the denominator)

Question 29

With which measure of disease (ratio, proportion, or rate) is time an intrinsic part of the denominator?

Answer 29

(A rate)

Question 30

What is prevalence?

Answer 30

(Prevalence measures the presence of existing cases of disease in a population during a specified time period → proportion of population who have the disease)

Question 31

Who are included in your numerator and denominator when calculating prevalence?

Answer 31

(Numerator - all current existing cases of the disease you are studying; denominator - the total population including healthy and sick)

Question 32

You have been observing a group of 118 veterinary students for lack of motivation for the month prior to winter break. During the first week, 23 students expressed a lack of motivation. During the second week, 64 students expressed a lack of motivation. During the third week, 87 students expressed a lack of motivation. During the fourth week, 31 students expressed a lack of motivation. What was the prevalence of lack of motivation during the third week (in english that a child would understand)?

Answer 32

(73% of the veterinary students were experiencing a lack of motivation during the third week of the month prior to winter break → since you are canceling out the units of time, you must include it in words with your answer)

Question 33

Who is excluded from the denominator when calculating incidence?

Answer 33

(People who are not at risk for the disease being measured → when measuring uterine cancer cases, individuals of the male sex are not included; this includes individuals who are already sick as they cannot be considered a ‘new’ case)

Question 34

Would you use the prevalence or incidence of a disease to assess the burden of the disease for the use of administration and planning, i.e. allocating resources appropriately?

Answer 34

(Prevalence)

Question 35

Would you use prevalence or incidence of a disease to evaluate treatments for a certain disease?

Answer 35

(Incidence, will tell you if the treatments are working, so you’d be looking for their state to change from diseased to non-diseased)

Question 36

How do prevalence and incidence differ in terms of what they are measuring?

Answer 36

(Prevalence - existing disease; incidence - new disease)

Question 37

What is the measurement of the occurrence of new cases of disease in a population during a specified time period?

Answer 37

(Cumulative incidence)

Question 38

What does an incidence rate measure?

Answer 38

(Incidence rate measures the speed at which new cases of disease occur in a population)

Question 39

Between cumulative incidence and incidence rate, which takes into account when disease occurs in the population followed?

Answer 39

(Incidence rate)

Question 40

What is the appropriate population type and follow up length that cumulative incidence can be used to measure disease?

Answer 40

(Fixed populations with a short follow up or no loss to follow up)

Question 41

What is person-time?

Answer 41

(The amount of time each person at risk for a disease is under observation; their accrual time ends when they are no longer at risk or the observation period ends)

Question 42

What is the formula for prevalence in relation to incidence rate?

Answer 42

(Prevalence (P) is approximately equal to incidence rate (IR) multiplied by the average duration of disease (D) → P ~= IR * D)

Question 43

(Dr. P q) Which type of disease frequency is expressed in the following statement: Percentage of nursing home residents who contracted influenza during the course of an outbreak (January 1-20, 2017).

Answer 43

(Cumulative incidence)

Question 44

(Dr. P q) Which type of disease frequency is expressed in the following statement: Percentage of potential army recruits rejected at intake exam because of poor vision.

Answer 44

(Prevalence)

Question 45

(Dr. P q) Which type of disease frequency is expressed in the following statement: Number of colds diagnosed in 1,000 person-years within an elementary school.

Answer 45

(Incidence rate)

Question 46

(Dr. P q) Which type of disease frequency is expressed in the following statement: Percent of live-born infants with a cardiac malformation among 100,000 live-births.

Answer 46

(Prevalence)

Question 47

(Dr. P q) A population of 100 healthy men was followed for the development of prostate cancer. Twenty men developed prostate cancer after being followed for 5 years. Another 10 men were followed for 1 year and then were lost to follow up. The remaining 70 men were followed for 10 years and never developed prostate cancer. Calculate the number of person-years of observation accrued by this population.

Answer 47

(810 person years; can check slide 71 of the measures of disease ppt if confused)

Question 48

(Dr. P q) (T/F) Only the population at risk contributes to the denominator of cumulative incidence.

Answer 48

(T)

Question 49

(Dr. P q) (T/F) When calculating the incidence rate of disease, it is necessary to follow subjects for the same amount of time.

Answer 49

(F)

Question 50

(Dr. P q) (T/F) If the incidence rate of a very serious disease is 75/100,000 person-years and the prevalence of disease in the population is 25/100,000 people, then the average duration of this disease must be 3 years.

Answer 50

(F, should be ⅓ year)

Question 51

(Dr. P q) (T/F) All other things being equal, when a treatment is developed that prolongs the life of people with a disease, the prevalence of the disease will increase over time.

Answer 51

(T)

Question 52

Does the sensitivity or specificity of a test represent the true negative rate of a diagnostic test?

Answer 52

(Specificity)

Question 53

(T/F) If a test is not precise, it cannot be accurate.

Answer 53

(T)

Question 54

(T/F) A test can be precise but that does not guarantee accuracy.

Answer 54

(T → consistently wrong)

Question 55

Compare and contrast true and apparent prevalence.

Answer 55

(True prevalence uses the gold standard positive cases (necropsy, bacterial culture, etc.) while the apparent prevalence uses the new test positive cases (which may include false positives))

Question 56

What test results/portions of the population (i.e. true positives, both true and false negatives, entire population, etc.) would you use for your numerator and denominator when trying to assess the true prevalence of disease in that sample population?

Answer 56

(Numerator is gold standard test positives (true positives and false negatives), denominator is entire population → you are calculating the proportion of all animals sampled that truly have the disease)

Question 57

What test results/portions of the population (i.e. true positives, both true and false negatives, entire population, etc.) would you use for your numerator and denominator when trying to assess the apparent prevalence of disease in that sample population?

Answer 57

(Numerator is true and false positives (all test positives) , denominator is entire population → you are calculating the proportion of animals sampled that appear to be infected based on the positive results from the new test)

Question 58

What test results/portions of the population (i.e. true positives, both true and false negatives, entire population, etc.) would you use for your numerator and denominator when you want to find the proportion of all animals tested that were correctly classified by the test kit?

Answer 58

(You are seeking accuracy, numerator would be true positives and true negatives, denominator would be entire population)

Question 59

What values need to be included in your numerator and denominator to calculate sensitivity?

Answer 59

(Numerator → true positives; denominator → all gold standard positives (so true positives plus false negatives))

Question 60

What values need to be included in your numerator and denominator to calculate specificity?

Answer 60

(Numerator → true negatives; denominator → all gold standard negatives (so true negatives plus false positives))

Question 61

What values need to be included in your numerator and denominator to calculate the positive predictive value of a test?

Answer 61

(Numerator → true positives; denominator → all test positives (so true positives plus false positives))

Question 62

What values need to be included in your numerator and denominator to calculate the negative predictive value of a test?

Answer 62

(Numerator → true negatives; denominator → all test negatives (so true negatives plus false negatives))

Question 63

If you are seeking the probability that a test subject with a positive test result is truly diseased, what value would you look at?

Answer 63

(Positive predictive value of the test; if you were seeking negative/truly undiseased → negative predictive value)

Question 64

If you are seeking the proportion of truly uninfected animals that test negative using a test kit, what value would you look at?

Answer 64

(Specificity; if you wanted positive instead → sensitivity)

Question 65

(T/F) As the prevalence of a disease falls, that will innately decrease your positive predictive value of a test and increase your negative predictive value of a test.

Answer 65

(T)

Question 66

Will your negative predictive value be higher or lower as sensitivity increases?

Answer 66

(Higher, as there are fewer false negatives/higher sensitivity your negative predictive value with be higher)

Question 67

What will result from a lower specificity, an increased or decreased positive predictive value?

Answer 67

(Decreased positive predictive value → lower specificity means more false positives and that results in a decreased positive predictive value)

Question 68

Describe sequential testing, the steps involved and what you are avoiding with each step.

Answer 68

(Start with a highly sensitive test, this avoids false negatives; test all those who tested positive with the highly sensitive test with a highly specific test, this avoids false positives; at the end you should end up with a population of close to if not 100% certainly positive individuals)

Question 69

Does parallel or series concurrent testing increase specificity of a test?

Answer 69

(Series → animal declared diseased only if it tests positive on both tests run; parallel = increased sensitivity → animal declared diseased if it tests positive on one or both tests)

Question 70

Who determines important requirements for animals entering different states?

Answer 70

(The state veterinarian aka chief state agricultural animal health officer)

Question 71

You are seeking a subject matter expert in zoonotic diseases, who would you turn to in your state?

Answer 71

(Your state public health veterinarian)

Question 72

What government sector contains the chief veterinary office for animal health for the United States, who is also the U.S. delegate for the WHOA?

Answer 72

(The USDA, specifically APHIS and more specifically the Veterinary Services → the head of the VS or the ‘deputy administrator’ is the CVO and WHOA delegate)

Question 73

Which subsector of the USDA protects consumers by ensuring that meat, poultry, and processed egg products are safe, wholesome, and accurately labeled?

Answer 73

(FSIS/Food Safety and Inspection Service)

Question 74

Who is the global authority on animal health that sets standards as opposed to laws?

Answer 74

(World Organization for Animal Health/WHOA)

Question 75

Is colostrum an example of passive or active immunity?

Answer 75

(Passive)

Question 76

Are vaccinations a form of passive or active immunity?

Answer 76

(Active)

Question 77

Is obtaining a disease and living a form of passive or active immunity?

Answer 77

(Active)

Question 78

With which type of vaccines is the cellular response variable?

Answer 78

(Inactivated/killed vaccines)

Question 79

Adjuvants are necessary for which type of vaccines?

Answer 79

(Inactivated/killed vaccines)

Question 80

Which vaccine type gets the best response but also has a chance of causing true disease?

Answer 80

(Modified live)

Question 81

What effect do intranasal vaccines have on pathogen shedding?

Answer 81

(Reduces it (if the shedding is related to the mucus membranes))

Question 82

Where are intramuscular vaccines administered in cattle?

Answer 82

(Cervical muscles always)

Question 83

Which side of a dog is the rabies vaccine administered?

Answer 83

(The right)

Question 84

Which side of a dog is the lepto vaccine administered?

Answer 84

(The left)

Question 85

How does perigestational vaccination differ in multiparous and primiparous dams?

Answer 85

(Multiparous dams are vaccinated at 3-4 weeks preparturition while primiparous dams are vaccinated at 6 and 3 weeks preparturition)

Question 86

For active immunity, how many weeks prior to an exposure event should an animal be vaccinated?

Answer 86

(3 weeks prior)

Question 87

You should be suspicious of a reportable disease when the morbidity and mortality are low/high (choose one).

Answer 87

(High)

Question 88

What types of skin lesions/conditions would make you suspicious of a reportable disease? Three answers.

Answer 88

(Vesicular, pox, or lumpy skin lesions/conditions)

Question 89

What level of response to treatment would make you suspicious of a reportable disease?

Answer 89

(Poor or no response to treatment)

Question 90

Avian diseases with what characteristics would make you suspicious of a reportable disease? Two answers.

Answer 90

(Avian disease with acute deaths and/or CNS signs)

Question 91

What are the three ‘epidemiologic investigation 101’ questions that you should ask once you have determined a disease outbreak has occurred?

Answer 91

(Where did the disease come from, what management factors allowed it to spread, and where did it go from here)

Question 92

Once a potential FAD is reported, who shows up and within what time period?

Answer 92

(A trained foreign animal disease diagnostician will be sent to the premises within 24 hours)

Question 93

To obtain the incidence risk ratio for a set of data, you need to divide the incidence risk of disease in the exposed by the incidence risk of disease in the unexposed, how do you get those values?

Answer 93

(You divide the exposed with disease by the total of exposed for incidence risk of disease in exposed; you divide the unexposed with disease by the total of unexposed for incidence risk of disease in the unexposed)

Question 94

What is the incidence risk ratio if I tell you that the risk of lack of motivation in veterinary students without iPads was 6 times greater than the risk of lack of motivation in veterinary students with iPads?

Answer 94

(The RR would be 6, I know this is kinda a dumb question but interpretations are important)

Question 95

What measure of strength will provide an estimate of how many times more likely exposed individuals will be diseased compared to non-exposed individuals?

Answer 95

(Incidence risk/rate ratio)

Question 96

(T/F) The risk ratio, the relative risk, and the incidence risk/rate ratio all mean the same thing.

Answer 96

(T)

Question 97

How do the odds ratio calculations differ for cohort and case-control studies?

Answer 97

(For cohort studies, you are comparing the odds of disease in the exposed versus unexposed where for case-control studies, you are comparing the odds of exposure in the diseased versus undiseased)

Question 98

How do you calculate the incidence risk of disease in the exposed that is attributable to the exposure?

Answer 98

(Subtract the incidence risk of the unexposed from the incidence risk of the exposed, this will give you attributable risk)

Question 99

How do you calculate the attributable fraction, which is the proportion of disease in the exposed that is due to the exposure?

Answer 99

(Incidence risk of exposed minus incidence risk of unexposed divided by the incidence risk of exposed)

Question 100

How do you calculate population attributable risk?

Answer 100

(Subtract the incidence risk of unexposed from the total incidence risk)

Question 101

What do you need to divide the population attributable risk by to get the population attributable fraction?

Answer 101

(The total incidence risk)

Question 102

A well built clinical research question has four architectural components, what are those components? (Hint: PICO).

Answer 102

(Patient or population, intervention (aka exposure), comparison intervention, and outcome)

Question 103

If you are starting a study in which you do not assign the exposures, you are utilizing comparison groups, and you start with the outcome and then search for exposure, what type of study design are you creating?

Answer 103

(Case-control study; if you were to instead go from exposure to outcome that would be a cohort)

Question 104

What is the term for bias that can occur if people who agree to take part in a study are different from the source population you want to study?

Answer 104

(Selection bias)

Question 105

What is the term for bias that can occur if study participants are placed into the wrong exposure or disease category?

Answer 105

(Misclassification or measurement error/bias → most common form and can be present in all types of studies)

Question 106

Of a differential or non-differential misclassification error, which will bias towards a null value only?

Answer 106

(Non-differential, differential will bias towards or away from a null value)

Question 107

What is the term for the bias that can occur if people with a disease remember/report their exposure differently than people without said disease?

Answer 107

(Recall bias)

Question 108

What is the term for the bias that can occur if there is a systematic difference in soliciting, recording, or interpreting information?

Answer 108

(Interviewer bias)

Question 109

What is the term for the branch of biology that deals with the relationships of organisms to one another and to their physical surroundings?

Answer 109

(Ecology)

Question 110

What is the term for the complex of living organisms, their physical environment, and all their interrelationships in a particular unit of space?

Answer 110

(Ecosystems)

Question 111

(T/F) Biodiversity can be used as an indicator of ecosystem health.

Answer 111

(T)

Question 112

Who is the global authority of species extinction risk?

Answer 112

(The International Union for Conservation of Nature/IUCN)

Question 113

What is the term for the study of underlying principles that influence the spatial and temporal patterns of diseases?

Answer 113

(Disease ecology)

Question 114

An emerging infectious disease is one that either has appeared in a population for the first time or what other scenario?

Answer 114

(One that may have existed previously but is rapidly increasing in incidence or geographic range)

Question 115

The drivers of disease emergence include ecological, social, and what other category of conditions that facilitate disease emergence and transmission?

Answer 115

(Economic)

Question 116

What is the main difference between surveillance and monitoring in terms of action?

Answer 116

(Surveillance implies an action will be performed based on the information collected whereas monitoring does not)