Investigators suspect that working in the west wing raised the risk of illness. What must the working case definition avoid?

1. A case definition decides who counts as a case; the analysis then asks which exposures the cases share. 2. Building the suspected exposure into the definition makes every case exposed by construction. 3. The comparison of west wing workers with everyone else then becomes impossible, so the west wing must stay out of the criteria. 4. The definition should instead cover illness among people who worked in the facility, and the analysis compares wings afterwards. 5. Restricting by date of onset is normal and expected in an outbreak definition. 6. Grades such as confirmed and probable, and clinical criteria, are standard parts of a case definition rather than errors. _Source: CDC Principles of Epidemiology in Public Health Practice, 3rd Edition, section Step 4 Construct a Working Case Definition_