The investigators decided to conduct a case-control study to test their hypotheses. Sixty-six persons met the case definition for a possible case and were still alive. Laboratory results had come back confirming Legionnaires' disease in 15 of these patients, and ruling out Legionnaires' disease in 10. Laboratory results for the remainder were pending.

• QUESTION 9:
  What case definition would you use for the case-control study?

• QUESTION 10:
  What are some possible sources of controls?