Chapter 2: The Dynamics of Disease Transmission

Question 1

Describe the types of disease transmission

Answer 1

Direct: person to person via direct contact Indirect: spread via a common vehicle such as contaminated air, water, or a vector (e.g. mosquito)

Question 2

Clinical Disease

Answer 2

Characterized by signs and symptoms

Question 3

Preclinical Disease

Answer 3

Disease that is not yet, but will progress be to clinical disease

Question 4

Subclinical Disease

Answer 4

Disease that is not clinical and is not destined to become clinical. Often diagnosed by antibody response or culture

Question 5

Persistent/Chronic Disease

Answer 5

An infection that persists for years

Question 6

Latent Disease

Answer 6

An infection with no active multiplication of the agent

Question 7

Carrier

Answer 7

Someone who harbors the organism but is not infected

Question 8

Endemic

Answer 8

The habitual presence of a disease within a geographic area

Question 9

Epidemic

Answer 9

The occurrence of a group of similar illnesses in a community or region

Question 10

Pandemic

Answer 10

A worldwide epidemic

Question 11

Herd Immunity

Answer 11

The resistance of a group of people to an attack by a disease to which a large proportion of the members of the group are immune

Question 12

Incubation Period

Answer 12

The time period between receipt of infection and the onset of symptoms

Question 13

What are some factors that can affect the length of the incubation period?

Answer 13

1. time needed for the organism to replicate 2. the site at which the organism replicates 3. the dose of the infectious agent received

Question 14

Attack Rate

Answer 14

Question 15

Food-Specific Attack Rate

Answer 15

Question 16

Using the tables, whate is the sore throat attack rate in persons who ate both egg salad and tuna?

Answer 16

60/75

Question 17

In the study of an outbreak of an infectious disease, why is plotting an epidemic curve useful?

Answer 17

• It helps to determine the type of outbreak (e.g. single source, person-to-person)
• It helps to determine the median incubation period

Question 18

Which of the following is characteristic of a single-exposure, common vehicle outbreak?

A. Frequent secondary cases

B. Increasing severity with increasing age

C. Explosive

D. Cases include both people who have been exposed and those who were not exposed

E. All of the above

Answer 18

C. The three characteristics of a single-exposure, common vehicle outbreak are:

1. It is explosive (since all cases are exposed at the same point in time, there is a sudden and rapid increase in the number of cases in a population)
2. The cases are limited to people who share the common exposure
3. Cases rarely occur in persons who acquire the disease from a primary case.

Question 19

Agent

Answer 19

the factor whose presences, excesive presence or relative absense is essiential for the disease to occrr

Question 20

Fomite

Answer 20

an inanimate object that can be the vehicle for transmission of an infectious agent (e.g. doorknobs, computer keys, telephones, IV drip lines, catheters

Question 21

Resevoir

Answer 21

The habitiat in which an infectious agent normally lives, grows, and multiplies; can include humans, animals, and enviornments

Question 22

Vector

Answer 22

a living intermediary that carries an agent from a reservoir to a susceptible host (mosquitos, fleas, ticks)

Question 23

Zoonosis

Answer 23

infectious disease that is transmissible from animals to humans

Question 24

What are the three critical variables in an outbreak investigation?

Answer 24

• When did the exposure take place?
• When did the disease begin?
• What was the incubation period?

Question 25

Comorbidity

Answer 25

the presences of other diseases/conditions that an individual patient might have in *addition* to the disease of primary interest

Question 26

Incidence

Answer 26

the number of **new** cases occurring in a defined population over a certain period

Question 27

Prevalance

Answer 27

the total burden of disease Prevalence = incidence x duration

Question 28

Premary Prevention

Answer 28

Prevents the illness from ever occurring

Question 29

Secondary Preention

Answer 29

mitigating the effects of the diseas (reucing onset, shortening duration, reducing transmission)

Question 30

Tertiary Prevention

Answer 30

Reduce the complications or effects of or cure the disease

Question 31

What are the steps in investigating an acute outbreak?

Answer 31

1. Define and validate the existence of an outbreak 2. Examine the distribution of cases 3. Look for combinations of relevant variables 4. Develop hypotheses 5. Test hypotheses 6. Recommend control measures 7. Write report 8. Communicate findings and implement policy