Deck 13: Epidemiology: Who, What, When, Where, and Why

Question 1

Describe the design of a case-control study and how it is used to identify the cause of an epidemic.

Answer 1

In a case-control study, each individual affected with a disease (a "case") is paired with an individual that is unaffected by the disease (a "control"). Each case-control pair should be as similar as possible in terms of age, sex, place of residence, and other factors that the investigators consider important. The only significant difference should be whether or not they are affected by the disease. Investigators then look for an additional characteristic or behavior that is common to all the cases, but is not observed in the controls. If such a factor is found, it can suggest to investigators why the cases were at risk for the disease while the controls were not. This information might suggest characteristics of the disease such as its mode of transmission that can help investigators narrow down the search for the disease agent.

Question 2

What is antigenic drift? Why are RNA viruses more prone to this phenomenon than DNA viruses are?

Answer 2

Antigenic drift refers to the gradual change in a virus' antigens, due to the accumulation of point mutations in the virus' genome. RNA viruses are especially prone to antigenic drift because the key enzyme involved in genome duplication, RNA polymerase, is incapable of proofreading. The DNA polymerase of DNA viruses, on the other hand, can detect and replace most of the point mutations it may introduce, greatly reducing the number of mutations that enter the genome. Consequently, changes in viral antigens are far less likely.

Question 3

Epidemic paralytic polio:

A) was more likely when newborns were exposed to the virus.
B) was more likely when exposure was delayed beyond infancy.
C) was most commonly seen in situations where sanitation was poor.
D) was eradicated in the United States as routine sanitation became commonplace.
E) has not been observed since the 19^th century in developed countries.

Answer 3

B

Question 4

Into which category of emergent diseases would dengue be placed?

A) Category 1: invasion of a new host population by a known pathogen
B) Category 2: appearance of a completely new, previously unknown pathogen
C) Category 3: association of a well-known disease with a new pathogen
D) Category 4: increased virulence, or a renewed problem, with a well-known but previously less virulent or well-controlled pathogen

Question 5

In which of the following types of viruses is antigenic shift most likely?
D) RNA viruses
E) DNA viruses
F) enveloped viruses
G) non-enveloped viruses h. viruses with a segmented genome

Question 6

The likelihood of a host-to-host epidemic is highest when:

A) the proportion of immune individuals in a population is below the epidemic threshold.
B) the proportion of immune individuals in a population is above the epidemic threshold.
C) the proportion of immune individuals in a population is at the epidemic threshold.
D) anytime the proportion of immune individuals in a population rises above 50%.
E) the second time a pathogen is introduced into a particular population.

Question 7

Which of the following pathogens would most likely be used as a bioterrorism agent?

A) Pathogen A: an obligate anaerobe
B) Pathogen B: an obligate aerobe
C) Pathogen C: a Gram-positive bacterial species
D) Pathogen D: a RNA virus
E) Pathogen E: a spore-former

Question 8

Which of the following is a characteristic of a commonsource epidemic?

A) Once the source is identified and controlled the last cases will occur approximately one incubation period later.
B) Once the source is identified and controlled there should be no additional cases.
C) The time between identification and control, and the last cases, depends on the transmission rate between sick and susceptible individuals.
D) When a common source epidemic begins, the number of cases rises slowly relative to a host-to-host epidemic.
E) When a common source epidemic ends, the number of cases falls slowly relative to a host-to-host epidemic.

Question 9

In the 1999 West Nile virus outbreak in New York City, which of the following pieces of evidence suggested that the pathogen under investigation was not St. Louis encephalitis (SLE)?

A) The time characteristic was not suggestive of SLE.
B) There was no mosquito involvement in this disease, as there would have been for SLE.
C) The viral particles were too small to be SLE.
D) Control measures initiated to control a SLE outbreak were not effective.
E) The case-control study indicated that this was not SLE.

Question 10

A particular type of virus occasionally undergoes antigenic shift. In which of the following situations is antigenic shift most likely?

A) when RNA polymerase makes a mistake, introducing an incorrect nucleotide
B) when the proofreading ability of RNA polymerase does not function properly
C) when a particular host cell is infected by a single strain of the virus
D) when a particular host cell is infected by two strains of the virus at the same time
E) when the proportion of immune individuals in the population is low

Question 11

How can a vaccine program prevent epidemics?

Question 12

When a new disease appears, which of the following is developed first?

A) a case-control study
B) personal characteristics of the disease
C) place characteristics of the disease
D) time characteristics of the disease
E) a case definition

Question 13

The incidence of disease:

A) is the total number of cases of a particular disease during an epidemic.
B) is calculated by subtracting the number of recovered individuals from the number of sick individuals.
C) is the number of new cases of a particular disease during a specified time period.
D) is the period of time measured in days, weeks, or years, during which an epidemic occurs.
E) is the average number of new cases infected by a single sick individual for a specific disease.