Epidemiology

Question 1

science that evaluates occurrence, determinants,
distribution, and control of health and disease in a defined
human population

Answer 1

Epidemiology

Question 2

occurs occasionally and at irregular intervals

example: histoplasmosis, gas gangrene

Answer 2

sporadic disease

Question 3

maintains a relatively steady low-level frequency at a moderately regular interval

(example: gonorrhea, Dengue fever)

Answer 3

endemic disease

Question 4

occurs at a high, constant level throughout a population

example: malaria

Answer 4

holoendemic diseases

Question 5

– sudden increase in frequency above expected number
– index case – first case in an epidemic

(example: influenza, meningococcal infections)

Answer 5

epidemic

Question 6

– sudden, unexpected occurrence of disease

– usually focal or in a limited segment of population

Answer 6

outbreak

Question 7

– increase in disease occurrence within large population over wide region
(usually worldwide)

Answer 7

pandemic

Question 8

• an incidence rate
Centers for Disease Control
• number of new cases in a specific time period per unit of population
(# new cases during a specific time/ # individuals in population) `

Answer 8

Morbidity rate

Question 9

• total number of individuals infected at any one time per unit of population
• depends both on incidence rate and duration of illness

Answer 9

Prevalence rate

Question 10

• number of deaths from a disease per number of cases of the disease

deaths due to given disease/ size of total population with disease

Answer 10

Mortality rate

Question 11

______ = number of secondary cases one case would produce in a completely susceptible population

Answer 11

R0 or R(0), “R-naught”

Question 12

What are the three parameters that used to calculate R(0)

Answer 12

• duration of contagiousness after a person becomes infected
• likelihood of infection per contact between a susceptible person
and an infectious person or vector • contact rate

Question 13

• involves use of surveillance methods

• cases of a disease recognized by its characteristic
disease syndrome
– set of signs and symptoms characteristic of a disease

– signs
• objective changes in body that can be directly observed

– symptoms
• subjective changes experienced by patient

Answer 13

Recognition of an Infectious Disease in a Population

Question 14

– period after pathogen entry but before signs and symptoms appear

Answer 14

• incubation period

Question 15

– onset of signs and symptoms

– not clear enough for diagnosis

Answer 15

• prodromal stage

Question 16

– disease is most severe and has characteristic signs and symptoms

Answer 16

• period of illness

Question 17

– signs and symptoms begin to disappear

Answer 17

• convalescence

Question 18

• after recognition of infectious disease in a population, outbreak
correlated with specific pathogen [e.g. HIV/AIDS (early 1980s), SARS
CoV (2003), SARS-CoV-2 (2019-2020)] • clinical microbiologists help in isolation and identification of pathogen

Answer 18

Correlation with a Single Causative Agent

Question 19

What are the two types of epidemics?

Answer 19

Common-source epidemic

propagated epidemic

Question 20

= minimum number of individuals necessary to continue propagating the disease

Answer 20

threshold density

Question 21

• resistance of a population to infection and to spread of an
infectious organism because of the immunity of a large percentage of the population

• level can be altered by introduction of new susceptible
individuals into population

• level can be altered by changes in pathogen

– antigenic shift – major change in antigenic character of pathogen

– antigenic drift – smaller antigenic changes

Answer 21

Herd immunity

Question 22

– can be transmitted from one

host to another

Answer 22

• communicable disease

Question 23

– location from which pathogen is transmitted to host

Answer 23

source

Question 24

– time during which source is
infectious or is disseminating
the organism

Answer 24

period of infectivity

Question 25

– site or natural environmental location in which pathogen is normally found

– sometimes functions as source of pathogen

Answer 25

reservoir

Question 26

– infected host
– can be casual (acute or transient)
carrier – short time – can be chronic carrier – long time

Answer 26

carrier

Question 27

have the overt clinical case of disease

Answer 27

active carrier

Question 28

– has recovered from disease but continues to harbor large numbers of pathogen

Answer 28

convalescent carrier

Question 29

– harbors pathogen but is not ill

Answer 29

healthy carrier

Question 30

– harbors pathogen but is not yet ill

Answer 30

incubatory carrier

Question 31

organisms that spread disease from one host to another

Answer 31

vector

Question 32

• pathogen suspended in air and travels >or = 1 meter

• droplet nuclei
– small particles (1-4 micrometers in diameter)
– can remain airborne for long time (hours to days)
– can travel long distances
– usually propelled from respiratory tract of source organisms by sneezing,
coughing, or vocalization

• dust particles also important route of airborne transmission

Answer 32

Airborne Transmission

Question 33

• coming together or touching of source/reservoir and host

• direct contact (person-to-person)
– physical interaction between source/reservoir and host
– e.g., kissing, touching, and sexual contact

• droplet spread
– large particles (>5 micrometers) that travel < 1 meter

Answer 33

Contact Transmission

Question 34

______= inanimate materials or objects involved in pathogen

transmission

Answer 34

Vehicles

Question 35

• inanimate materials or objects involved in pathogen transmission

– water and food (spread pathogen to multiple hosts)

– fomites = inanimate objects: surgical instruments, bedding and eating utensils

Answer 35

vehicle transmission

Question 36

– passive carriage of pathogen on body of vector

– no growth of pathogen during transmission

Answer 36

• external (mechanical) transmission

Question 37

– carried within vector
– harborage transmission
– pathogen does not undergo changes within
vector (bubonic plaque: Yersinia pestis in flea) – biologic transmission – pathogen undergoes changes within vector
(malaria: Plasmodium spp. in Anopheles spp. mosquito)

Answer 37

internal transmission

Question 38

What are the two main factors in determining why the host was susceptible to the pathogen?

Answer 38

– defense mechanisms of host

– pathogenicity of pathogen

Question 39

– movement of pathogen to portal of exit [helminths (worms) that migrate through the body of the host]

Answer 39

active escape

Question 40

– excretion in feces, urine, droplets, saliva, or

desquamated cells [microbes]

Answer 40

• passive escape

Question 41

1. Reduce or eliminate source or reservoir
2. Break connection between source and susceptible individuals
3. Reduce number of susceptible individuals

Answer 41

Control of Epidemics

Question 42

ways to Reduce or eliminate source or reservoir

Answer 42

– quarantine and isolation of cases and carriers
– destruction of animal reservoir
– treatment of sewage
– therapy that reduces or eliminates infectivity of cases

Question 43

Ways to Break connection between source and susceptible individuals

Answer 43

– chlorination of water supplies
– pasteurization of milk
– supervision & inspection of food & food handlers
– destruction of insect vectors with pesticides

Question 44

ways to Reduce number of susceptible individuals

Answer 44

– passive immunity following exposure
– active immunity for protection

together these result in an augmented herd immunity