CBIC Outbreak Investigation 5 — Questions and Answers
Question 1: Which scenario BEST represents a propagated outbreak pattern?
- Thirty patients develop gastroenteritis after eating contaminated potato salad at a single event
- New norovirus cases continue to appear on a hospital ward over several weeks through person-to-person spread (Correct answer)
- A contaminated ice machine causes a cluster of Legionella cases over two days
- A single batch of IV fluid causes bloodstream infections in multiple patients
Correct answer: New norovirus cases continue to appear on a hospital ward over several weeks through person-to-person spread
A propagated outbreak is sustained by person-to-person transmission, producing a gradually rising epidemic curve that extends beyond one incubation period.
Question 2: Environmental sampling during an outbreak investigation is MOST appropriate when:
- All cases have already recovered
- An environmental reservoir is suspected based on epidemiological evidence (Correct answer)
- Antibiotic stewardship data are unavailable
- The outbreak has been declared over
Correct answer: An environmental reservoir is suspected based on epidemiological evidence
Environmental cultures should be targeted and hypothesis-driven, collected only when epidemiological evidence points to a specific environmental source.
Question 3: A hospital investigates a cluster of Legionella pneumophila infections. Which environmental source requires PRIORITY sampling?
- Door handles and bed rails
- Potable water system and cooling towers (Correct answer)
- HVAC return air filters
- Sink drains in patient rooms only
Correct answer: Potable water system and cooling towers
Legionella thrives in potable water systems and cooling towers, which are the primary reservoirs linked to healthcare-associated Legionnaires' disease.
Question 4: When an infection preventionist applies the 'Bradford Hill criteria' during outbreak analysis, they are assessing:
- Proper PPE donning sequence for responders
- Strength of evidence for a causal relationship between exposure and disease (Correct answer)
- Laboratory confirmation standards for reportable diseases
- Criteria for mandatory patient isolation
Correct answer: Strength of evidence for a causal relationship between exposure and disease
The Bradford Hill criteria provide a framework (strength, consistency, specificity, temporality, etc.) for judging whether an observed association is likely causal.
Question 5: During an outbreak, an IP identifies that cases are clustered among patients of one specific nurse. This finding MOST likely indicates:
- A waterborne transmission route
- Possible healthcare worker colonization or breach in technique (Correct answer)
- An issue with the facility's HVAC system
- Contaminated parenteral nutrition prepared in the pharmacy
Correct answer: Possible healthcare worker colonization or breach in technique
Clustering of infections around a single HCW raises concern for colonization of that worker or consistent lapses in infection prevention technique.
Question 6: Which action is part of the 'control and prevention' phase of an outbreak investigation rather than the investigative phase?
- Developing a case definition
- Implementing enhanced hand hygiene audits and contact precautions (Correct answer)
- Constructing an epidemic curve
- Conducting a case-control study
Correct answer: Implementing enhanced hand hygiene audits and contact precautions
Implementing enhanced hand hygiene audits and contact precautions are control interventions; case definitions, epidemic curves, and analytic studies are investigative tools.
Question 7: An IP uses Pulsed-Field Gel Electrophoresis (PFGE) during an MRSA outbreak. What is the PRIMARY purpose of this test?
- Determine MIC values for vancomycin
- Establish genetic relatedness between MRSA isolates (Correct answer)
- Screen healthcare workers for active infection
- Detect MRSA directly from environmental surfaces
Correct answer: Establish genetic relatedness between MRSA isolates
PFGE is a molecular typing method that generates DNA fingerprints of bacterial isolates, allowing investigators to determine if outbreak strains are genetically related.
CBIC Outbreak Investigation 5
Which scenario BEST represents a propagated outbreak pattern?