Epidemiology Flashcards

Which of the following best describes the 'iceberg phenomenon' in infectious disease epidemiology?

Answer: Most infections in a community are subclinical and go undetected

The iceberg phenomenon describes how clinical cases represent only the visible 'tip' of all infections, while the majority — subclinical and mild cases — remain undetected below the surface.

When comparing HAI rates between two ICUs with different patient populations, which statistical method best adjusts for differences in intrinsic patient risk?

Answer: Standardized infection ratio with risk adjustment

Risk-adjusted standardized infection ratios use multivariate models or stratification to account for patient-level risk factors, enabling fair comparisons across facilities with different case mixes.

In an investigation of a suspected nosocomial Clostridium difficile outbreak, which case definition component is essential for the initial case count?

Answer: Symptom criteria combined with laboratory confirmation and healthcare exposure criteria

A sound case definition combines clinical criteria (diarrhea), laboratory confirmation (positive toxin or PCR), and an epidemiological link (healthcare exposure) to ensure cases are counted consistently and accurately.

Which epidemiological concept explains why routine screening programs for low-prevalence infections often yield many false-positive results even with high-specificity tests?

Answer: Positive predictive value decline with low prevalence

When disease prevalence is low, even highly specific tests produce many false positives relative to true positives, dramatically reducing the positive predictive value (PPV) of the test.

A prospective study follows 500 uninfected patients for 6 months; 50 develop SSI. What is the cumulative incidence of SSI?

Answer: 10%

Cumulative incidence = new cases / total at-risk population at the start = 50 / 500 = 0.10, or 10%, over the 6-month follow-up period.

Which surveillance strategy is most effective for detecting emerging antimicrobial resistance patterns in a healthcare facility?

Answer: Laboratory-based surveillance with regular antibiogram review

Laboratory-based surveillance integrating all culture and susceptibility data with regular antibiogram analysis provides real-time, comprehensive detection of emerging resistance patterns across the entire facility.

In descriptive epidemiology, the triad of 'person, place, and time' is used primarily to accomplish which goal?

Answer: Generate hypotheses about the source and spread of disease

Characterizing cases by person (who), place (where), and time (when) generates hypotheses about the cause, source, and mode of transmission that guide subsequent analytic investigations.