CIC Outbreak Investigation 3 — Questions and Answers
Question 1: In a hospital outbreak of Serratia marcescens in a neonatal ICU, which source is most commonly implicated?
- Contaminated breast milk from the milk bank
- Shared multi-dose medication vials or contaminated IV fluids (Correct answer)
- HVAC systems and hospital water supply
- Visitor hand hygiene non-compliance
Correct answer: Shared multi-dose medication vials or contaminated IV fluids
Serratia marcescens outbreaks in NICUs are frequently linked to contaminated multi-dose medication vials, IV fluids, or infusion equipment.
Question 2: Which statistical test is most appropriate to determine if the difference in attack rates between exposed and unexposed groups is statistically significant?
- Student's t-test
- Chi-square test or Fisher's exact test (Correct answer)
- ANOVA
- Pearson correlation coefficient
Correct answer: Chi-square test or Fisher's exact test
Chi-square test (or Fisher's exact test for small cell counts) is used to compare proportions such as attack rates between two groups in outbreak investigations.
Question 3: An ICP notes that a unit has had 5 MRSA infections in the past month compared to a baseline of 1 per month. What is the FIRST action?
- Immediately implement contact precautions on all patients
- Confirm case definitions and review whether cases meet healthcare-associated criteria (Correct answer)
- Notify infection control committee and close the unit
- Order point prevalence surveillance cultures on all patients
Correct answer: Confirm case definitions and review whether cases meet healthcare-associated criteria
Before declaring an outbreak, the ICP must first confirm case definitions and verify that cases are true healthcare-associated infections to avoid pseudo-outbreaks.
Question 4: Which molecular typing method is considered the gold standard for clonal relatedness in outbreak investigations of Staphylococcus aureus?
- Pulsed-field gel electrophoresis (PFGE)
- Whole genome sequencing (WGS) (Correct answer)
- Multilocus sequence typing (MLST)
- Repetitive element PCR (rep-PCR)
Correct answer: Whole genome sequencing (WGS)
Whole genome sequencing is now considered the most discriminatory method for determining clonal relatedness and is increasingly used as the gold standard in outbreak investigations.
Question 5: During a COVID-19 outbreak investigation in a hospital, what is the primary purpose of contact tracing?
- To determine the source of the initial case
- To identify exposed individuals and implement quarantine or monitoring (Correct answer)
- To calculate the basic reproduction number (R0)
- To determine the incubation period of the pathogen
Correct answer: To identify exposed individuals and implement quarantine or monitoring
Contact tracing identifies individuals exposed to confirmed cases so they can be quarantined, monitored for symptoms, and tested to break chains of transmission.
Question 6: A pseudo-outbreak of Mycobacterium gordonae is detected in bronchoscopy patients. What is the most likely explanation?
- Patient-to-patient transmission via droplet nuclei
- Contamination of bronchoscopes during reprocessing with tap water (Correct answer)
- Contamination of bronchoscopy suction canister with patient secretions
- Environmental acquisition from hospital HVAC system
Correct answer: Contamination of bronchoscopes during reprocessing with tap water
M. gordonae is a waterborne nontuberculous mycobacterium that commonly contaminates bronchoscopes when tap water is used during rinsing after reprocessing.
Question 7: When generating hypotheses about the source of a foodborne outbreak, which tool is most useful for initially capturing potential exposures?
- Line listing with demographic data only
- Open-ended interviews with early cases using a hypothesis-generating questionnaire (Correct answer)
- Retrospective chart review of all hospitalized patients
- Environmental sampling of suspected food items
Correct answer: Open-ended interviews with early cases using a hypothesis-generating questionnaire
Open-ended interviews with early cases using a broadly-designed questionnaire help generate hypotheses about potential exposures before analytical studies are conducted.
CIC Outbreak Investigation 3
In a hospital outbreak of Serratia marcescens in a neonatal ICU, which source is most commonly implicated?