CIC Outbreak Investigation 2 — Questions and Answers
Question 1: Which measure is used to quantify the association between an exposure and illness in a cohort study during an outbreak investigation?
- Odds ratio
- Relative risk (Correct answer)
- Attack rate difference
- Chi-square statistic
Correct answer: Relative risk
Relative risk (risk ratio) is the measure of association used in cohort studies, comparing the risk of illness among exposed versus unexposed individuals.
Question 2: During an outbreak of Clostridioides difficile in a long-term care facility, which environmental surface is most commonly implicated as a reservoir?
- Stainless steel bed rails
- Bedrails and call buttons touched by gloved hands
- Toilet seats, commodes, and bathroom surfaces (Correct answer)
- HVAC vents and ceiling tiles
Correct answer: Toilet seats, commodes, and bathroom surfaces
C. difficile spores persist on environmental surfaces especially in bathrooms and can survive for months, making toilets and commodes common reservoirs.
Question 3: An epidemic curve showing a prolonged plateau with cases continuing over several weeks most likely indicates which type of outbreak?
- Point-source outbreak
- Propagated person-to-person outbreak
- Continuous common-source outbreak (Correct answer)
- Mixed-source outbreak
Correct answer: Continuous common-source outbreak
A continuous common-source outbreak produces a prolonged plateau on the epidemic curve because ongoing exposure to the contaminated source continues over time.
Question 4: When calculating an attack rate stratified by exposure status, what is the primary purpose of stratification?
- To increase the sample size of the study
- To identify confounding variables and effect modifiers (Correct answer)
- To determine the incubation period
- To establish the index case
Correct answer: To identify confounding variables and effect modifiers
Stratification helps identify confounders and effect modifiers by examining whether the exposure-disease association differs across subgroups.
Question 5: A foodborne outbreak affects guests at a wedding reception. Which investigative approach would best identify the implicated food item?
- Environmental cultures of all kitchen surfaces
- Cohort study with food-specific attack rates among attendees (Correct answer)
- Case-control study comparing cases to non-attendees
- Genomic sequencing of all food samples
Correct answer: Cohort study with food-specific attack rates among attendees
A cohort study calculating food-specific attack rates among all attendees is the most efficient method when the exposed population is well-defined and enumerable.
Question 6: Which of the following best defines a 'cluster' in epidemiological terms during an outbreak investigation?
- Three or more cases of any illness in a facility within 30 days
- An aggregation of cases in a defined place and time that may or may not exceed the expected number (Correct answer)
- Cases linked by molecular typing to a single source
- Any group of healthcare-associated infections above the baseline rate
Correct answer: An aggregation of cases in a defined place and time that may or may not exceed the expected number
A cluster is an aggregation of cases in a defined place and time that may or may not exceed the expected background rate and may or may not have a common cause.
Question 7: During outbreak investigation, which step should occur BEFORE implementing control measures?
- Publishing the outbreak findings in a peer-reviewed journal
- Verifying the diagnosis through laboratory confirmation (Correct answer)
- Notifying the state health department of the outbreak
- Conducting environmental rounds to identify reservoirs
Correct answer: Verifying the diagnosis through laboratory confirmation
Verifying the diagnosis through laboratory confirmation is essential before implementing targeted control measures to ensure appropriate interventions are applied.
CIC Outbreak Investigation 2
Which measure is used to quantify the association between an exposure and illness in a cohort study during an outbreak investigation?