In investigating a Serratia marcescens outbreak in a surgical ICU, which tool is most appropriate to determine plausible causes?

• A. Fishbone diagram
• B. Scatter plot
• C. Flowchart
• D. Pareto chart

Answer: (A)

In outbreak investigations, you want a structured way to brainstorm and organize all potential causes so you can test them systematically. A cause-and-effect diagram, often called a fishbone diagram, is ideal for this. It helps a multidisciplinary team lay out broad categories—such as environment, equipment, personnel, procedures, and materials—and then drill down into specific factors within each category. This visual layout makes it easier to see where plausible causes might lie, identify gaps in data, and guide targeted data collection and testing (for example, environmental sampling, reviewing cleaning protocols, or inspecting supply chains).

Other tools answer different questions. A scatter plot looks for relationships between two variables and isn’t designed to generate or organize possible causes. A flowchart maps the sequence of steps in a process, which is useful for spotting where a breakdown might occur but doesn’t systematically surface multiple potential causes. A Pareto chart helps prioritize issues by frequency or impact after causes have been identified, not for initial cause discovery.

So for a Serratia marcescens outbreak in a surgical ICU, using a fishbone diagram supports comprehensive, collaborative thinking about all plausible sources—environmental factors, equipment and devices, procedural practices, medications or solutions, and personnel practices—before moving on to data collection and hypothesis testing.