The essential and preventive role of indoor climate management for infection control in hospitals will be discussed with special emphasis on relative humidity. Each year in the US and worldwide, healthcare-associated infections kill more people than do automobile accidents (Reed and Kemmerly, 2009; Anderson, 2013). New data are presented showing an association between indoor humidity above 40 percent and reduced healthcare-associated infections. Current infection prevention strategies are discussed with consideration of this new insight. Managing indoor air relative humidity in hospitals could prevent a significant percentage of healthcare-associated infections. This prevention strategy is equally applicable to office and residential buildings.