In rapid outbreak investigation, which step follows construction of the line list?

• A. Develop and test hypotheses
• B. Confirm outbreak
• C. Implement immediate control measures
• D. Establish case definition

Answer: (D)

The key idea is that a clear, standardized case definition is used to determine who is counted as a case, which makes the data in the line list consistent and comparable. A line list simply records details about identified cases, but without a defined criterion for what counts as a case, the entries may be inconsistent or incomplete. Establishing the case definition sets the inclusion criteria that all subsequent case finding and data collection should follow, and it also allows any existing line-list entries to be reviewed or reclassified if needed. After the case definition is in place, you can continue with identifying additional cases and performing descriptive analyses to understand the outbreak’s pattern.

Other steps—confirming that an outbreak exists, testing hypotheses, implementing control measures—occur at different points in the investigation and typically come after establishing a consistent case definition and compiling descriptive data.