CBIC Epidemiology 5 — Questions and Answers
Question 1: Which of the following best describes the 'iceberg phenomenon' in infectious disease epidemiology?
- The majority of infections are severe and clinically apparent
- Most infections in a community are subclinical and go undetected (Correct answer)
- Pathogens are detected only after causing visible environmental contamination
- Outbreaks are discovered only after the peak has passed
Correct 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.
Question 2: When comparing HAI rates between two ICUs with different patient populations, which statistical method best adjusts for differences in intrinsic patient risk?
- Chi-square test
- Standardized infection ratio with risk adjustment (Correct answer)
- Independent t-test
- Pearson correlation coefficient
Correct 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.
Question 3: In an investigation of a suspected nosocomial Clostridium difficile outbreak, which case definition component is essential for the initial case count?
- Positive stool culture only
- Symptom criteria combined with laboratory confirmation and healthcare exposure criteria (Correct answer)
- Any diarrhea occurring during hospitalization
- Positive toxin assay regardless of symptom status
Correct 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.
Question 4: Which epidemiological concept explains why routine screening programs for low-prevalence infections often yield many false-positive results even with high-specificity tests?
- Sensitivity paradox
- Positive predictive value decline with low prevalence (Correct answer)
- Specificity-sensitivity trade-off
- Selection bias in screening populations
Correct 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.
Question 5: A prospective study follows 500 uninfected patients for 6 months; 50 develop SSI. What is the cumulative incidence of SSI?
- 5%
- 10% (Correct answer)
- 50%
- 15%
Correct 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.
Question 6: Which surveillance strategy is most effective for detecting emerging antimicrobial resistance patterns in a healthcare facility?
- Targeted surveillance of ICU patients only
- Passive voluntary physician reporting
- Laboratory-based surveillance with regular antibiogram review (Correct answer)
- Point prevalence surveys conducted annually
Correct 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.
Question 7: In descriptive epidemiology, the triad of 'person, place, and time' is used primarily to accomplish which goal?
- Establish causality between exposure and outcome
- Generate hypotheses about the source and spread of disease (Correct answer)
- Calculate incidence rates for comparison
- Confirm laboratory diagnostic findings
Correct 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.
CBIC Epidemiology 5
Which of the following best describes the 'iceberg phenomenon' in infectious disease epidemiology?