An "outbreak" of Legionnaires' disease means that how many person(s) were exposed to Legionella in the same place and became ill around the same time?

An "outbreak" of Legionnaires' disease is typically defined as two or more individuals who are exposed to the same source of Legionella and subsequently become ill in a similar timeframe. This definition is crucial for public health responses and investigations since it indicates that there is a common source of infection that may need to be addressed to prevent further cases.

In this context, the correct choice of two people as the minimum to define an outbreak underscores the nature of infectious diseases and how they are monitored and managed. Identifying two cases helps health authorities to trace the source and potentially contain the outbreak effectively. Having just one case would not constitute an outbreak, as it does not imply a shared source of exposure. Thus, the correct identification of what constitutes an outbreak is key to understanding how public health systems respond to Legionnaires' disease and similar infectious diseases.