A, Floor plan of the Centers for Disease Control and Prevention (CDC) laboratory at Bo. Room 1 is the clean room, used for preparation of polymerase chain reaction (PCR) master mix and reagents for RNA extraction, room 2 is used for RNA extraction and the addition of RNA to PCR plates, and room 3 is an office area with thermocyclers, used for performing the PCR reactions and for data analysis. Work is undertaken in a unidirectional flow, from room 1 to room 2 to room 3.