BayCare Health System, the leading healthcare player in Tampa Bay, expects to acquire another hospital for the first time since its creation 15 years ago, expanding its reach into Polk County. BayCare officials said Wednesday they plan to purchase Winter Haven Hospital. The nonprofit BayCare currently operates the St. Joseph's hospitals in Tampa, St. Anthony's in St. Petersburg and the Morton Plant Mease hospitals in mid Pinellas. BayCare controls more than a third of the hospital business in the Tampa Bay market, but Winter Haven marks its first hospital outside its core communities in Pinellas, Hillsborough and Pasco.