Epidemiology Flashcards

Which epidemiological measure describes the probability that a person without a disease will develop that disease over a specified time period?

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.

In a healthcare outbreak investigation, what is the purpose of calculating an 'epidemic curve'?

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.

A hospital reports 15 new CLABSI cases per 1,000 central line-days. This is an example of which epidemiological rate?

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.

Which concept explains why an infection control program may see an apparent increase in HAI rates after implementing better surveillance methods?

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.

In the context of HAI surveillance, what does a 'standardized infection ratio' (SIR) less than 1.0 indicate?

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.

Which type of study design is most appropriate for investigating a rare disease with a long latency period?

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.

What does the 'herd immunity threshold' represent in infectious disease epidemiology?

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.