CBIC Epidemiology 2 — Questions and Answers
Question 1: Which epidemiological measure describes the probability that a person without a disease will develop that disease over a specified time period?
- Prevalence rate
- Cumulative incidence (Correct answer)
- Attack rate
- Case fatality rate
Correct answer: Cumulative incidence
Cumulative incidence (also called incidence proportion) measures the probability of developing a disease over a defined period among those initially at risk.
Question 2: In a healthcare outbreak investigation, what is the purpose of calculating an 'epidemic curve'?
- To identify the causative pathogen
- To visualize the pattern and timing of cases over time (Correct answer)
- To calculate antibiotic susceptibility rates
- To determine the cost of the outbreak
Correct answer: To visualize the pattern and timing of cases over time
An epidemic curve is a histogram that plots the number of cases by date of onset, revealing the pattern, magnitude, and potential source (common source vs. propagated) of an outbreak.
Question 3: A hospital reports 15 new CLABSI cases per 1,000 central line-days. This is an example of which epidemiological rate?
- Crude rate
- Specific rate (Correct answer)
- Standardized rate
- Proportional rate
Correct answer: Specific rate
A specific rate uses a defined denominator (central line-days) that is specific to the population at risk, making it more meaningful than a crude rate for device-associated infections.
Question 4: Which concept explains why an infection control program may see an apparent increase in HAI rates after implementing better surveillance methods?
- Berkson's bias
- Detection bias
- Ascertainment bias (Correct answer)
- Selection bias
Correct answer: Ascertainment bias
Ascertainment bias occurs when improved detection methods identify cases that previously went unrecognized, causing an apparent rise in rates that reflects better surveillance rather than a true increase.
Question 5: In the context of HAI surveillance, what does a 'standardized infection ratio' (SIR) less than 1.0 indicate?
- The facility has more infections than predicted
- The facility has fewer infections than predicted (Correct answer)
- The facility's data is incomplete
- The surveillance methodology is flawed
Correct answer: The facility has fewer infections than predicted
An SIR less than 1.0 means the observed number of infections is lower than the predicted number based on national benchmark data, suggesting better-than-expected performance.
Question 6: Which type of study design is most appropriate for investigating a rare disease with a long latency period?
- Randomized controlled trial
- Cross-sectional study
- Case-control study (Correct answer)
- Cohort study
Correct answer: Case-control study
Case-control studies are ideal for rare diseases because they start with known cases and matched controls, avoiding the need to follow large populations for long periods.
Question 7: What does the 'herd immunity threshold' represent in infectious disease epidemiology?
- The minimum number of vaccinated individuals needed to prevent all infections
- The proportion of a population that must be immune to stop sustained transmission (Correct answer)
- The dose of pathogen required to infect 50% of exposed hosts
- The attack rate in an unvaccinated community
Correct answer: The proportion of a population that must be immune to stop sustained transmission
The herd immunity threshold is the critical proportion of immune individuals in a population required to reduce the effective reproduction number below 1, halting sustained disease transmission.
CBIC Epidemiology 2
Which epidemiological measure describes the probability that a person without a disease will develop that disease over a specified time period?