CBIC Outbreak Investigation 2 — Questions and Answers
Question 1: During an outbreak investigation, which epidemiological measure best describes the proportion of exposed persons who develop the disease?
- Attack rate (Correct answer)
- Incidence density
- Prevalence rate
- Mortality rate
Correct answer: Attack rate
The attack rate is the proportion of exposed individuals who develop illness during a specific outbreak period.
Question 2: A cluster of surgical site infections is identified in a hospital. What is the FIRST step in a formal outbreak investigation?
- Implement immediate control measures
- Verify the diagnosis and confirm the outbreak exists (Correct answer)
- Notify the state health department
- Collect environmental cultures
Correct answer: Verify the diagnosis and confirm the outbreak exists
Verifying the diagnosis and confirming a true outbreak (vs. pseudooutbreak or surveillance artifact) is always the first step.
Question 3: Which type of epidemic curve shape is most consistent with a common-source, point-source outbreak?
- Plateau over several weeks
- Gradual rise and slow decline
- Sharp rise with a rapid fall within one incubation period (Correct answer)
- Multiple peaks separated by the incubation period
Correct answer: Sharp rise with a rapid fall within one incubation period
A point-source outbreak produces a sharp, narrow epidemic curve because all exposures occur at essentially the same time.
Question 4: An infection preventionist notes that Clostridioides difficile rates on a unit have tripled. Before declaring an outbreak, which action should be taken FIRST?
- Culture all healthcare workers on the unit
- Review changes in testing methods or case definitions (Correct answer)
- Place the entire unit on contact precautions
- Report the cluster to the CDC
Correct answer: Review changes in testing methods or case definitions
Changes in testing platforms or case definitions can create pseudooutbreaks; these must be ruled out before an investigation begins.
Question 5: In outbreak investigation, a case-control study is most useful when:
- The disease is common and the outbreak is large
- The number of cases is small and the source is unknown (Correct answer)
- Environmental cultures have already identified the pathogen
- The attack rate exceeds 50% of the exposed population
Correct answer: The number of cases is small and the source is unknown
Case-control studies are efficient when cases are few, allowing comparison of exposures between cases and matched controls to identify the source.
Question 6: Which organism is MOST commonly associated with a pseudooutbreak caused by contaminated bronchoscope rinse water?
- Staphylococcus aureus
- Mycobacterium spp. (Correct answer)
- Candida albicans
- Enterococcus faecium
Correct answer: Mycobacterium spp.
Nontuberculous mycobacteria (Mycobacterium spp.) are classic pseudooutbreak culprits linked to contaminated bronchoscope rinse water or ice machines.
Question 7: When constructing a line listing during an outbreak investigation, which data element is LEAST essential?
- Date of symptom onset
- Patient's insurance provider (Correct answer)
- Exposure history
- Culture results
Correct answer: Patient's insurance provider
Insurance information is administrative and has no epidemiological relevance to identifying the source, mode of transmission, or case definition.
CBIC Outbreak Investigation 2
During an outbreak investigation, which epidemiological measure best describes the proportion of exposed persons who develop the disease?