Epidemiology Final Exam Material Flashcards by Chris Bessette

The majority of cases of human rabies in the USA are caused by:

Bats

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T/F: Prevalence is a measure of the amount of disease in a population

True

This includes all cases, old and new, relative to the entire population. It is used clinically to estimate the probablity that an animal is diseased

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T/F: Prevalence is a measure of the rate of disease occurence

False

Prevalence is a measure of the amount of disease in a population

Incidence is a measure of the rate of disease occurence

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The proportion of cases that are fatal within a specified time folllwing disease onset or diagnosis is termed:

Case Fatality Rate

Example: 3 of 467 people (0.03%) with Bartonella hensellae infections died during the follow up period

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T/F: Sensitivity and Specificity are not influenced by prevalence

True

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In case-control and cross-sectional studies, what is the measure of association used to measure exposure in the diseased and non-diseased groups?

Odd Ratio

This is the ratio of the number exposed to the number not exposed

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Name the governmental organization responsible for safety of shell eggs produced in the USA?

FDA

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You’re about to eat a delicious blueberry scone after performing a gloveless rectal exam on a 175 pound great dane with the shits. Should you wash your hands before eating the scone?

Who knows?! It’s a MYSTERY

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T/F: Reed-Frost models can not be used for continuously changing population sizes

True

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T/F: In an epidemiologic study, if the subjects were not given a treatment or an exposure, this is an example of an experimental study

False

This would be an example of an _observational_ study.

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T/F: With retrospective cohort studies, it is important to make sure that NO subject has the outcome (disease) at the beginning of the study

False

With prospective cohort studies, it is important to make sure that NO subject has the outcome (disease) at the beginning of the study*
With retrospective cohort studies, the researchers must blind themselves to the disease status of the subjects because they may already have the outcome (disease)*

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________ is the number of secondary cases caused by an infected individual in an entirely susceptible population

R₀ (basic reproductive #)

Determines whether a disease can persist, and is valuable for assessing management options. It suggests the average number of new cases that should be caused by each existing case

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A bias that equally affects groups is a _________ bias

non-differential

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One disadvantage to ecological studies is the concept of ecological fallacy. Describe what ecological fallacy is:

Relationships observed at the population level may not hold true at the individual level

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If you’re performing a cohort study and subjects are selected based on their exposure, then their outcome status is determined from their history (by reviewing records, tests, etc), what type of study is this?

Retrospective Cohort Study

Measure of association in this case is prevalence ratio (because the disease has already occurred)

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Identify the term used to describe the proportion of disease-free (susceptible) individuals in a population who became diseased during a specified period of time:

Cumulative incidence

This is interpreted as the probability (risk) of a susceptible individual becoming diseased during the study period

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If you’re performing an observational analytical study and you select a sample of individual subjects because they have the exposure you are studying, what type of study is this?

Cohort Study

Individual subjects are selected because of their exposure status.

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Is a Chi-squared test used for categorical or continuous data?

Categorical Data

This is a test of independence between two categorical variables

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Which bacterial genus is most often associated with egg-borne disease?

Salmonella

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Rate is an expression of the change in the amount of disease in a defined population per unit of time. What are the most common ‘rates’ in scientific papers?

**Cumulative Incidence **and Incidence Density

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T/F: Farms that sell table eggs must have a control program in place for Salmonella Enteritidis (SE)

True

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The “one-handed scoop technique” is:

A method of seduction
A technique used while recapping a needle to prevent needle stick injuries
An 18th century dance move
A training course at Cold Stone Creamery

A technique used while recapping a needle to prevent needle stick injuries

If it is absolutely necessary to recap a needle, you should either use forceps or the “one handed scoop technique:” hold the syringe with the attached needle and scoop the cap, which is lying on a flat surface, onto the needle’s sharp end. Tighten by pushing it against an object or by pulling the base of the needle cap onto the hub of the needle with the same hand holding the syringe

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What is considered to be the single most important measure to reduce the risk of disease transmission in a veterinary clinic?

Hand Hygeine

(using soap and water or alcohol-based products)*
Hand washing is preferred in veterinary settings because hands are routinely contaminated with organic material*

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How do you calculate specificity?

This is the proportion of non-diseased animals the test correctly classifies as negative

If you test 100 non-diseased animals and 98 of them are negative by the test, specificity would be 98%

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When an unknown factor distorts the relationship between the exposure and outcome, this is called:

**confounding**

What is the most important reservoir for rabies in the Caribbean?

**Mongoose**

If you read the following statement in a journal article, how is it interpreted? ## Footnote **Prevalence of disease was 8% (95% CI: 4.0-12.0%)**

**The _estimate_ of the prevalence of the study was 8%, but we are 95% confident that the _true prevalence_ lies somewhere between 4.0% and 12.0%**

The width of the confidence interval in a study is relative to the sample size of the study. Would you expect small samples to have large or small CIs?

**Small samples have _large_ CIs.** **Large samples have ****_small_ CIs.**

If you're performing an observational analytical study and you select a sample of individual subjects to **represent a population**, what type of study is this?

**Cross Sectional Study**

In an observational epidemiologic study, if you're observing a **group of** **populations** (as opposed to a group of individuals), what kind of study is this?

**Ecological** * In an ecological study, individual people or animals are not tested or questioned or measured in any way* * \*\*IMPORTANT: NO measurements are made on individuals - they are all measured at the population level\*\**

What are the three components to calculate R₀?

**R₀ = (Number of 'contacts' per day) x (Probability of transmission per 'contact') x (Duration [days] of infection)** *R₀ increased is ANY of these three element increase*

What is the most common salmonellosis in the USA? What food product is it most associated with?

***Salmonella enteritidis*** *Eggs*

For **observational analytical** studies, there are three types of studies based on the reason for selecting study subjects. What are the three types of **observational analytical** studies?

* **Cross-sectional** * **Case Control** * **Cohort**

The smaller the sample size, the ______ the confidence interval

The smaller the sample size, the **_larger_** the confidence interval

T/F: Even as the prevalence of disease changes, PPV and NPV will remain the same

**False** PPV (positive predictive value) and NPV (negative predictive value) change as the prevalence of the disease changes

If you're performing an observational analytical study and you select a sample of individual subjects **because they have the outcome you are studying**, what type of study is this?

**Case-Control Study**

How do you calculate **sensitivity**?

Sensitivity is the proportion of diseased animals that the test correctly classifies as **positive** ## Footnote *If you test 100 diseased animals and 95 of them are positive by the test, the sensitivity would be 95%*

Cumulative incidence during an epidemic is known as:

**Attack Rate**

T/F: If the 95% confidence interval for an **odds ratio (OR)** includes '1,' then the OR is _not_ statistically significant

**True** * For instance, "the Odds Ratio was 3 (95% CI: 0.5-6.0)" would not be statistically significant, because '1' is included in the range of '0.5-6.0'* * \*\*This rule is the same for _Relative Risk_** as well\*\**

Is a **Students T-test** used for categorical or continuous data?

**Continuous Data** *Used to compare the means of a value for two different (independent) groups*

A bias that affects one group more than the other is a _________ bias

**Differential**

In order to be statistically significant, a P-value must be less than \_\_\_\_\_\_

**0.05** *P-values are used to estimate whether a measured association was likely to have been caused by chance*. *If the P-value is greater than 0.05, the association is not statistically significant and could have been caused by chance*

*Salmonella* enteritidis in humans is primarily caused by ingestion of:

**raw or undercooked eggs**

Name the governmental organization responsible for safety of egg *products* and imported shell eggs?

**USDA**

If you're performing a cohort study and subjects are selected based on their exposure, then followed in time to determine if they develop the outcome, what type of study is this?

**Prospective Cohort Study** ## Footnote *The measure of association in this case is 'relative risk'*

Name the legislation that mandates the inspection of eggs and egg products for safety and adulteration?

**Egg Product Inspection Act (EPIA)**

T/F: The EPIA mandates quality assurance of eggs in the USA

**False** The EPIA only mandates that eggs must be SAFE and not unhealthy. The EPIA does not regulate quality assurance

The level of herd immunity needed to control disease varies. *Approximately \_\_\_\_% immunity is required for highly infectious diseases*

The level of herd immunity needed to control disease varies. Approximately **_95%_** immunity is required for highly infectious diseases

The prevalence of death in a given time period is termed:

**Mortality Rate**

What is the single most important **global** animal reservoir for **rabies**?

**Dogs**

What is the most common needle stick injury in veterinary clinics?

**Inadvertent injection of a vaccine** *(usually from trying to recap a needle)*

What is the pH of newly laid eggs?

**7.6 - 7.9**

When measuring disease occurance, the persons or animals included in the measurement are called the:

**study population**

Name the term used to interpret the probability that an individual in the study population **is diseased** at the time of the study

**Point Prevalence** *This is the most common measure of prevalence and is often determined by cross-sectional studies and surveys*

What are the three most commonly reported accidents/injuries in a veterinary clinic?

**Cat bites, dog bites, needle sticks**

In a scientific paper, a clear and objective presentation of the findings with no interpretation would be found in *which section*?

**Results**

What is considered the best observational study design for determining **risk factors**?

**Prospective Cohort Studies**

T/F: in **case-control** and **cross-sectional** studies, the exposure and disease have already occurred when the study begins, so we can not measure incidence

**True**

If there are 10 diseased animals and 3 of them are exposed, what are the odds of exposure in the diseased group?

**3/7**

T/F: If the **odds ratio** is equal to 1, this is indicative of a strong association

**False** *OR=1 means the odds of exposure among cases was equal to that of the controls. _If OR=1, there is no association_.*

When using a two-by-two table, what is the formula for calculating the **odds ratio**?

**OR = (ad)/(bc)** *OR is called the "cross-product ratio" because you multiply diagonally, which forms an X*

When using a two-by-two table, what is the formula for calculating **relative risk**?

**RR = [a/(a+b)] / [c/c+d)]**

The amount or proportion of overall disease incidence in a population or group that can be attributed to a specific exposure is termed:

**Attributable Risk (AR)** *Results are interpreted: “\_\_\_\_% of the overall disease incidence can be attributed to this particular exposure” *

If there are 10 exposed animals and 3 of them are diseased, what is the **prevalence** of disease in the exposed group?

**3/10** *Prevalence is the measure used to compare the amount of disease that occurred in the exposed and unexposed groups in retrospective studies *

What are the two types of **error** in scientific studies?

* **Random Error** (due to chance) * **Systematic Error** (due to bias)

What two methods do we use to estimate how much random variation there is in our study and whether our result is likely to have been caused by chance?

**Confidence Intervals **and **P-values**

T/F: If the 95% CI for the OR does not include 1, the OR is statistically significant

**True**

The ‘hypothesis of no association’ (i.e. there is no association between exposure and disease) is termed:

**Null Hypothesis (H₀)** We use P-values or CIs to accept or reject the Null Hypothesis. The level of statistical significance is 95% p = 0.05. * **If p-value is less than 0.05:** Reject the Null Hypothesis and accept the Alternative Hypothesis * **If p-value is greater than 0.05:** Accept the Null Hypothesis and reject the Alternative Hypotheses

The ‘research question’ (i.e. that there is an association between exposure and disease) is termed:

**Alternative Hypothesis (H_a)**

Rejecting the null when it is NOT false (i.e. no association exists) is *what type of error*?

**Type I (α) Error: FALSE POSITIVE**

Not rejecting the null hypothesis when it is false (i.e. an association truthfully exists) is *what type of error*?

**Type II (β) Error: FALSE NEGATIVE**

T/F: A correlation between two variables is considered strong if the correlation coefficient (r) is greater than 0.8

**True** *the correlation coefficient (r) Indicates the strength and direction of a linear relationship between two variables*

Name the federal agency that regulates shell egg safety in the USA:

**FDA**

Name the federal agency that regulates the safety of egg products and **imported** shell eggs in the USA:

**USDA**

For healthy milk, what is the acceptable somatic cell count per mL of milk?

**\<100,000/mL**

For Grade A cow's milk in the USA, what is the **legal maximum** somatic cell count per mL of milk in the bulk tank?

**750,000 cells/mL**

What is the #1 cowside test to screen for mastitis?

**California Mastitis Test (CMT)**

Pasteurization is currently based on the thermal death of:

***Coxiella burnetti *** *Of all microbes found in milk, this is the most difficult pathogen to kill with heat.*

T/F: *Taenia solium* is almost always generalized and the carcass condemned

**True**

Name the fish toxin associated with histamine fish poisoning:

**Scombrotoxin**

T/F: Hepatitis A infection in infancy or childhood is asymptomatic

**True**

How is Hepatitis A transmitted?

**Fecal-Oral**

What is the most common cause of foodborne illness worldwide?

**Norovirus!** *Infected food handlers are the most important vehicle for transmission. The virus is hardy, surviving at least a week on counters/surfaces*

What is the most common cause of severe diarrhea in children around the world?

**Rotavirus**

How do humans get cysticercosis?

**Consuming *Taenia solium***** eggs!!** ## Footnote *Taenia solium is the leading cause of seizure epilepsy in the developing world*

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 is termed:

**Epidemiology** *It's pretty much the name of the class*

Associations measured in studies can be a result of three things. What are they?

* The exposure truly causes the outcome (disease) * Random error * Systematic error