CBIC Outbreak Investigation 3 — Questions and Answers
Question 1: During a foodborne outbreak investigation at a hospital cafeteria, which analytical study design calculates a relative risk directly?
- Case-control study
- Cohort study (Correct answer)
- Cross-sectional prevalence survey
- Ecological study
Correct answer: Cohort study
A cohort study follows exposed and unexposed groups forward, allowing direct calculation of incidence rates and relative risk.
Question 2: A hospital is investigating an MRSA outbreak on an ICU. Whole-genome sequencing of isolates is used to:
- Determine antibiotic susceptibility patterns
- Assess clonality and transmission chains among cases (Correct answer)
- Replace standard contact precautions during the investigation
- Identify environmental reservoirs without culture
Correct answer: Assess clonality and transmission chains among cases
Whole-genome sequencing identifies genetic relatedness of isolates, helping trace transmission chains and confirm clonal outbreaks.
Question 3: Which measure should an IP use to compare infection rates between units with different patient populations?
- Crude infection count
- Risk-adjusted or stratified infection rates (Correct answer)
- Incubation period analysis
- Simple prevalence survey
Correct answer: Risk-adjusted or stratified infection rates
Risk adjustment or stratification accounts for differences in patient acuity and exposure time, enabling valid comparisons across units.
Question 4: An outbreak of gram-negative bacteremia is linked to contaminated IV fluids. Which investigation step confirms the vehicle?
- Reviewing hand hygiene compliance logs
- Matching the molecular type of patient isolates to product cultures (Correct answer)
- Auditing catheter insertion technique
- Performing environmental air sampling
Correct answer: Matching the molecular type of patient isolates to product cultures
Demonstrating identical molecular fingerprints between patient isolates and the suspected contaminated product confirms the transmission vehicle.
Question 5: In a healthcare-associated outbreak, 'generation time' refers to:
- The time from hospital admission to symptom onset
- The average time between successive cases in a transmission chain (Correct answer)
- The duration of patient isolation
- The time required to identify a cluster via surveillance
Correct answer: The average time between successive cases in a transmission chain
Generation time is the interval between the infection of a primary case and the infection of secondary cases, helping characterize person-to-person spread.
Question 6: A cluster of Klebsiella pneumoniae carbapenemase (KPC) infections appears in a neonatal ICU. Which intervention is MOST critical during active investigation?
- Discontinue all antibiotic use on the unit
- Implement contact precautions and cohort affected patients (Correct answer)
- Close the unit to new admissions permanently
- Switch to oral vancomycin prophylaxis for all neonates
Correct answer: Implement contact precautions and cohort affected patients
Contact precautions combined with cohorting patients and staff are the cornerstone of controlling carbapenem-resistant organism outbreaks during investigation.
Question 7: Which statistical concept helps determine whether the number of observed cases in an outbreak exceeds what would be expected by chance alone?
- Sensitivity analysis
- Control chart / statistical process control (Correct answer)
- Incubation period calculation
- Positive predictive value
Correct answer: Control chart / statistical process control
Control charts using statistical process control help distinguish true signals (excess cases) from normal variation in infection rates.
CBIC Outbreak Investigation 3
During a foodborne outbreak investigation at a hospital cafeteria, which analytical study design calculates a relative risk directly?