CIC Surveillance & Epidemiologic Investigation 4 — Questions and Answers
Question 1: When constructing a case definition during an outbreak investigation, which element is NOT typically included?
- Person characteristics
- Place of exposure
- Treatment protocol used (Correct answer)
- Time frame
Correct answer: Treatment protocol used
Case definitions include person, place, and time criteria; the treatment protocol is not part of defining a case.
Question 2: Which concept describes the ability of a surveillance system to detect outbreaks or increases in infection rates in a timely manner?
- Specificity
- Representativeness
- Timeliness
- Sensitivity (Correct answer)
Correct answer: Sensitivity
In surveillance system evaluation, sensitivity refers to the system's ability to detect true cases and outbreaks that actually occur.
Question 3: A hospital observes a sudden increase in MRSA bacteremia. Whole-genome sequencing (WGS) reveals identical strains in all cases. What does this finding suggest?
- Sporadic unrelated acquisitions
- A common-source or clonal outbreak (Correct answer)
- Environmental contamination with multiple strains
- Laboratory cross-contamination only
Correct answer: A common-source or clonal outbreak
Identical WGS profiles indicate clonal transmission, suggesting a common source or person-to-person spread of a single strain.
Question 4: Which NHSN event type requires that the patient has no evidence of infection on admission and signs/symptoms appear on or after the third calendar day of admission?
- Community-acquired infection
- Healthcare-associated infection (HAI) (Correct answer)
- Present-on-admission infection
- Incubating infection
Correct answer: Healthcare-associated infection (HAI)
NHSN defines an HAI as one where signs/symptoms appear on calendar day 3 or later, indicating healthcare onset.
Question 5: An IP reviews lab data and notices a spike in C. difficile positives. Before declaring an outbreak, which alternative explanation should be ruled out first?
- Increased hand hygiene compliance
- A change in testing methodology or ordering practices (Correct answer)
- Reduction in antibiotic use
- New environmental cleaning products
Correct answer: A change in testing methodology or ordering practices
A change in testing method (e.g., switching to a more sensitive PCR assay) or increased ordering can produce apparent spikes without true disease increase.
Question 6: Which measure of central tendency is MOST influenced by extreme outlier values in infection rate data?
- Median
- Mode
- Mean (Correct answer)
- Geometric mean
Correct answer: Mean
The arithmetic mean is highly sensitive to extreme outliers, which can pull the average significantly away from the typical value.
Question 7: During an outbreak of gram-negative BSIs in an ICU, molecular typing reveals two distinct strain clusters. This finding is BEST described as:
- A single-source outbreak
- Two concurrent but separate outbreaks (Correct answer)
- Endemic baseline variation
- Laboratory contamination artifact
Correct answer: Two concurrent but separate outbreaks
Two genetically distinct clusters occurring simultaneously suggest two separate outbreak events running concurrently in the same unit.
CIC Surveillance & Epidemiologic Investigation 4
When constructing a case definition during an outbreak investigation, which element is NOT typically included?