Outbreak Investigation Flashcards

A nursing unit reports 5 cases of influenza-like illness within 48 hours. What is the FIRST step the Infection Preventionist (IP) should take?

Answer: Verify the diagnoses and establish a preliminary case definition.

The foundational step in any outbreak investigation is to first confirm that the reported cases share a consistent diagnosis and to create a working case definition. This ensures the investigation is focused on a single, specific problem. Implementing control measures, conducting extensive reviews, or notifying health departments happens after this initial verification confirms an outbreak is likely.

An IP creates an epidemic curve for an outbreak of norovirus on a rehabilitation unit. The curve shows a rapid increase in cases over 24-48 hours, followed by a gradual decline, with no clear evidence of wave-like patterns. What is the most likely mode of transmission suggested by this curve?

Answer: Point source

A point source epidemic curve is characterized by a sharp upslope and a more gradual downslope, indicating that a group of people was exposed to a common infectious agent over a very brief period (e.g., a single contaminated meal or event). A propagated (person-to-person) source would show progressively taller peaks, a continuous common source would show a sustained plateau, and an intermittent source would have irregular peaks.

When creating a line list during the investigation of a healthcare-associated infection outbreak, which of the following data elements is MOST crucial for descriptive epidemiology?

Answer: Date of symptom onset.

A line list is a table containing key information on each case in an outbreak. The date of symptom onset is essential for the 'time' component of descriptive epidemiology (person, place, time), allowing the IP to create an epidemic curve and determine the outbreak's timeline. While other information is collected, the onset date is fundamental to the epidemiological investigation.

At a hospital potluck, 80 staff members ate potato salad and 20 did not. Of those who ate the potato salad, 40 developed gastroenteritis. Of those who did not eat the potato salad, 2 developed gastroenteritis. What is the attack rate among those who ate the potato salad?

Answer: 50%

The attack rate is calculated as (Number of new cases among an exposed group) / (Total number of people in that exposed group) x 100. In this scenario, it is (40 people who got sick after eating the salad) / (80 people who ate the salad) = 0.50, or 50%. This calculation is a key step in identifying the likely source of a foodborne outbreak.

Which of the following is the most important characteristic of a case definition during the initial phase of an outbreak investigation?

Answer: It should be broad and sensitive to capture all potential cases for further investigation.

Initially, it is crucial to use a sensitive (or broad) case definition to ensure that all potential cases are identified for investigation. This approach casts a wide net to avoid missing cases. As more information is gathered, including laboratory results, the case definition can be refined and made more specific. Starting too specific can cause cases to be missed, hampering the investigation.

After investigating a cluster of Pseudomonas aeruginosa bloodstream infections in the ICU, the IP's descriptive epidemiology reveals that all affected patients had a central line and were located in the same wing of the unit. What is the most appropriate next step in the investigation?

Answer: Develop a hypothesis and conduct analytic studies, such as observing central line care practices.

Descriptive epidemiology (person, place, time) helps to generate hypotheses about the cause of an outbreak. The findings point toward a potential issue with central line care. The next logical step is to formulate a specific hypothesis (e.g., 'The outbreak is caused by a breach in aseptic technique') and then test it through analytic epidemiology, which could include a case-control study or direct observation of practices. Making conclusions or implementing widespread interventions without testing the hypothesis is premature.