Legionella and spas?

How is Legionella contracted from spas/hot tubs and what actions ensure that this never happens?  We deal in portable spas and there has been an article in the national paper recently stating that a person has died through infection from a spa.

Problems occur when biocides are not used or they are used at ineffective concentrations.  The American Society of Heating, Refrigeration Air-conditioning Engineers (ASHRAE) has a section on spas and hot tubs in their publication “Minimizing the Risk of Legionellosis in Building Water Systems”.  You can get a  copy from ASHRAE or from the Baltimore Aircoil web site www.baltimoreaircoil.com.