Epidemiology of Infectious Diseases

Question 1

Epidemiology (definition)

Answer 1

The study of the distribution and determinants of health-related states or events in specified population, and the application of this study to the control of health problems

Also involves applying the knowledge gained by the studies to community-based practice to come up with acceptable public health intervention to control and prevent disease in the community

Question 2

Epidemiology Purposes in Public Health Practice

Answer 2

• Discover the pathogen, host & environmental factors that affect health
• Identify those segments of the population that have the greatest risk
• Evaluate the effectiveness of health programs & services in controlling infectious diseases

Question 3

Attack Rate

Answer 3

Attack Rate = ill/exposed

AR = Number of people at risk who develop disease / Number of people at risk during a specified time period

Question 4

Survellience

Answer 4

The collection of data pertaining to factors contributing to the occurrence of diseases of diseases in populations 
These include:
-Pathogens
-Hosts
-Reservoirs
-Vectors
-Mechanisms of spread 
Prediction of the extent of spread

Question 5

Classification of infectious diseases in populations:

• Sporadic
• Endemic
• Epidemic
• Pandemic

Answer 5

Sporadic: occasional, from time to time infrequently and irregularly

Endemic: constant presence of a disease or infectious agent within a given geographic area
–Random, unpredictable, isolated cases

Epidemic: (outbreak): disease occurrence among a population that is in excess of what is expected in a given time or place (sudden higher than normal incidence)

Pandemic: epidemic that spread through many areas of the world involving very large numbers of persons within a short period; spreads across regions, for instance multiple continents

Question 6

Two Types of Epidemics:

1. Common Source
2. Propagated

Answer 6

Common Source: explosive outbreak (ex. food poisoning)

Propagated: progressive (ex. person to person break, ex. strep throat)

Question 7

Case
Primary Case
Secondary Case
Index Case

Answer 7

Case: a person who has been diagnosed as having a disease, disorder, injury or condition
Primary Case: the person who brings the infection to a population
Secondary Case: persons who are infected by the primary case (from contact w/ the primary case)
Index Case: the first disease case brought to the attention of the epidemiologist (NOT ALWAYS THE PRIMARY CASE)

Question 8

Basic Reproductive Rate (R0)

Answer 8

Average number of secondary cases of infection arising from a primary case in a COMPLETELY susceptible population

Question 9

R0 < 1
R0 = 1
R0 > 1

Answer 9

R0 < 1 … disease will die out
R0 = 1 … endemic
R0 > 1 … epidemic

Question 10

R0 = p x c x d

Answer 10

p = probability of transmission per contact
c = contacts per unit time
d= duration of infectiousness

Question 11

Effective Reproductive Rate (R)

Answer 11

Average number of secondary cases per infectious case in a population made up for both SUSCEPTIBLE and NON-SUSCEPTIBLE hosts
-Variable/partial susceptibility

Question 12

Effective Reproductive Rate (R) = proportion susceptive x R0

Answer 12

What determines R?

• p
• c
• d
• The proportion of the population that is already immune

Question 13

Herd Immunity

Answer 13

The indirect protection from infection of susceptible members of a population, and the protection of the population as a whole, which is brought about by the presence of immune individuals