Epidemiology (I) Basics

Question 1

What are the five objectives of epidemiology?

Answer 1

To identify the etiology, extent, natural history and prognosis, and treatment options related to disease(s) in order to develop public policy

Question 2

What is the purpose of an epidemiological study of disease etiology?

Answer 2

To reduce morbidity and mortality by identifying risk factors and causative agents

Question 3

What is the purpose of an epidemiological study of the extent of disease?

Answer 3

Used for health systems planning and prioritizing health programs based on disease burden

Question 4

What is the purpose of an epidemiological study of disease natural history and prognosis?

Answer 4

To answer patient questions about survival and the severity of a disease; to provide information about screening; to provide a baseline to compare future treatments

Question 5

What is primary prevention?

Answer 5

Preventing the onset of disease

Question 6

What is secondary prevention?

Answer 6

Screening for asymptomatic (but diseased) individuals

Question 7

What is tertiary prevention?

Answer 7

Disease treatment

Question 8

What is first-step epidemiology?

Answer 8

Descriptive epidemiology

Question 9

What is second-step epidemiology?

Answer 9

Analytic epidemiology

Question 10

What is the main question in descriptive epidemiology?

Answer 10

Is there an association (correlation) between two or more factors? (hypothesis generating)

Question 11

What is the main question in analytic epidemiology?

Answer 11

Is the identified association causal? (hypothesis testing)

Question 12

What is experimental epidemiology?

Answer 12

Clinical trials – Evaluation of the effectiveness of an intervention and/or preventative and therapeutic programs

Question 13

What are the three corners of the epidemiologic triangle?

Answer 13

Host, environment, agent

Question 14

What is in the center of the epidemiologic triangle?

Answer 14

A vector or vehicle

Question 15

Are vectors alive or dead?

Answer 15

Alive (organisms)

Question 16

Are vehicles alive or dead?

Answer 16

Dead (inanimate objects or substances)

Question 17

What are some categories of disease-causing agents?

Answer 17

Biological, chemical, physical, nutritional

Question 18

What is direct disease transmission?

Answer 18

Human-to-human

Question 19

What is indirect disease transmission?

Answer 19

A common source (vehicle) or vector transmits the disease

Question 20

What is it called when an individual is infected but shows no signs or symptoms?

Answer 20

Subclinical infection

Question 21

What is it called when a person is chronically infected with continued low-grade survival and multiplication of the agent (e.g. HIV or typhoid)?

Answer 21

Persistent infection

Question 22

What is it called when a person is infected with an agent with no active multiplication of the agent (as when viral nucleic acid is integrated into the nucleus of a cell as a provirus)?

Answer 22

Latent infection

In contrast with a persistent infection, only the genetic message is present in the host, not viable organisms

Question 23

What is a carrier?

Answer 23

A host infected with an organism that is asymptomatic but capable of transmitting disease (e.g. Hepatitis B or HHSV)

Question 24

What is the period from exposure to symptoms when the organism is actively replicating?

Answer 24

Incubation period

Question 25

For what are epidemic curves useful?

Answer 25

Identifying the:

– Occurrence of an epidemic

– Time and source of exposure

– Mode of transmission

– Causative agent

Question 26

What type of exposure might cause a sharp epidemic curve in which cases start suddenly and then taper off quickly?

Answer 26

A common-source outbreak (e.g. norovirus on a cruise ship)

Question 27

What epidemic curve would describe a common-vehicle, continuous exposure?

Answer 27

A more drawn-out, lasting curve that starts slowly and then pewters out over time

Question 28

What is the equation for herd immunity (Q_c)?

Answer 28

Q_c = 1 - 1 / R_o

Question 29

What are the requirements for herd immunity to be met? (4 main points)

Answer 29

– Disease agent restricted to a single host species within which transmission occurs

– Relatively direct transmission from an infected person to a susceptible person (if other reservoirs are possible, herd immunity doesn’t work)

– Infections / immunizations must induce solid immunity

– Outbreaks occur in randomly mixing populations (i.e. infected persons are not more likely than the general population to contact susceptible people)

Question 30

What is the equation for attack rate?

Answer 30

AR = ( # of at-risk people who develop disease ) / ( total # of at-risk people )

Note: this is a proportion, not a true rate

Question 31

What is the equation for a food-specific attack rate?

Answer 31

AR = (# at-risk who ate the food and developed disease) / (total # of people at-risk who ate the food)

Question 32

What is a secondary attack rate?

Answer 32

The attack rate in susceptible people who are exposed to a primary case.

Question 33

What is a herd immunity threshold?

Answer 33

The threshold is the % of people that need to be vaccinated to reach herd immunity.

Question 34

What is R₀ (basic reproduction number)?

Answer 34

The average number of people to whom an infected individual will transmit the disease.

Question 35

What is an index case?

Answer 35

The first case in a family or other defined group to come to the attention of the investigator (a sentinel case)

Question 36

What is a case definition?

Answer 36

Criteria that must be met for the patient to qualify as having the disease

• Doctors diagnosis (ICD codes)
• Physical exams
• Laboratory tests

Question 37

What is the ICD?

Answer 37

The International Classification of Disease (currently on the 11th edition)