Epidemiology Flashcards

Which of the following best describes 'confounding' in an epidemiological study of HAIs?

Answer: A third variable that is associated with both the exposure and the outcome

Confounding occurs when a third variable is independently associated with both the exposure and the outcome, potentially distorting the true relationship between them.

In outbreak investigation, a 'propagated epidemic curve' with successive waves of increasing case counts typically indicates which transmission pattern?

Answer: Person-to-person spread with progressive secondary cases

A propagated curve with successive peaks separated by one incubation period indicates person-to-person transmission, where secondary and tertiary cases generate new waves.

What is the primary purpose of stratified analysis in HAI epidemiological studies?

Answer: To identify and control for confounding variables

Stratified analysis examines the association between exposure and outcome within subgroups defined by potential confounders, allowing assessment and control of confounding effects.

A cluster of Legionella cases in a hospital is linked to the cooling tower. Which epidemiological term best describes this type of HAI source?

Answer: Common vehicle

A common vehicle refers to a single contaminated source (such as water, food, or equipment) that transmits infection to multiple people, which is the mode for Legionella via cooling towers.

Which statistical measure indicates the minimum detectable effect size that a study is powered to identify at a given alpha level?

Answer: Statistical power

Statistical power (typically 80% or higher) is the probability of detecting a true effect of a given magnitude; it determines whether a study is adequately sized to identify meaningful differences.

In NHSN HAI surveillance, which denominator is used for calculating the CAUTI rate?

Answer: Urinary catheter-days

NHSN calculates CAUTI rates per 1,000 urinary catheter-days, which accounts for the device-specific risk exposure time and allows meaningful comparisons across facilities.

Which measure of disease frequency accounts for the time each individual is at risk and is expressed per person-time unit?

Answer: Incidence density rate

Incidence density (incidence rate) uses person-time as the denominator, accounting for the varying lengths of time different individuals are observed and at risk.