Q: Which of the following equations correctly represents the calculation of the case fatality ratio (CFR)?

$$\text{CFR} = \frac{\text{Number of deaths from a disease}}{\text{Number of diagnosed cases}} \times 100$$

Question 1

Which of the following best describes the difference between incidence and prevalence of a disease?

Accepted Answer

Incidence is the number of people who develop a disease during a particular time period, while prevalence is the number of people who have a disease at a specified time, regardless of when it first appeared.

Question 2

A patient develops a severe intestinal infection with Clostridium difficile after a course of broad-spectrum antibiotics. Which concept best explains why this occurred?

Accepted Answer

The antibiotics reduced the normal microbiota, allowing C. difficile to proliferate due to loss of microbial antagonism.

Question 3

Which of the following is an example of mutualism in the human microbiome?

Accepted Answer

Escherichia coli in the large intestine synthesizing vitamin K for the host while obtaining nutrients.

Question 4

A disease that is constantly present in a population, such as malaria in certain regions, is best described as:

Accepted Answer

Endemic

Question 5

Which of the following equations correctly represents the calculation of the case fatality ratio (CFR)?

Accepted Answer

$$	ext{CFR} = \frac{	ext{Number of deaths from a disease}}{	ext{Number of diagnosed cases}} 	imes 100$$

Question 6

Which of the following is NOT a factor that influences the composition of the normal microbiota?

Accepted Answer

Blood type

Question 7

A hospital patient develops pneumonia after being on a ventilator for several days. This infection is best classified as:

Accepted Answer

A healthcare-associated infection (HAI)

Question 8

Which of the following best describes the prodromal period of a disease?

Accepted Answer

A short period after incubation with early, mild, nonspecific symptoms

Question 9

Which of the following is an example of indirect contact transmission?

Accepted Answer

A patient acquiring MRSA from a contaminated stethoscope

Question 10

Which of the following is a key reason why emerging infectious diseases are often zoonotic and vector-borne?

Accepted Answer

Animal reservoirs and arthropod vectors facilitate the spread and evolution of new pathogens

Question 11

Which of the following is NOT a step in Koch’s postulates?

Accepted Answer

The pathogen must be transmitted by a vector to a new host.

Question 12

A patient is infected with a virus but shows no noticeable signs or symptoms. This type of infection is best described as:

Accepted Answer

Subclinical infection

Question 13

Which of the following best describes herd immunity?

Accepted Answer

Immunity in most of a population, reducing the likelihood of disease spread

Question 14

Which of the following is an example of vehicle transmission?

Accepted Answer

A person drinking contaminated water and developing cholera

Question 15

Which of the following is a plausible reason why some pathogens cannot be proven to cause disease using Koch’s postulates?

Accepted Answer

Some pathogens cannot be grown in pure culture.

Question 16

A patient with HIV develops pneumonia caused by Pneumocystis jirovecii. The pneumonia in this case is best described as:

Accepted Answer

A secondary (opportunistic) infection

Question 17

Which of the following is the correct formula for calculating the infection fatality ratio (IFR)?

Accepted Answer

$$	ext{IFR} = \frac{	ext{Number of deaths attributed to a disease}}{	ext{Total number of infected individuals}} 	imes 100$$

Question 18

Which of the following is a standard precaution for controlling healthcare-associated infections (HAIs)?

Accepted Answer

Using hand hygiene before and after patient contact

Question 19

Which of the following best describes the role of descriptive epidemiology?

Accepted Answer

It collects and analyzes data to determine patterns of disease occurrence.

Question 20

A fly lands on contaminated feces and then on a hamburger bun, transferring bacteria. This is an example of:

Accepted Answer

Mechanical vector transmission

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