The bad flu season is finally showing signs of easing up for most Americans. But for senior-housing companies, the worst is yet to come.During earning calls this month, senior-housing operators and landlords have lamented a harsh flu season that has led ailing residents to move out of their facilities and forced operators to temporarily close their doors to admissions for fear of spreading the virus.Cindy Baier, chief financial officer of Brentwood, Tenn.-based Brookdale Senior Living Inc., the largest owner and operator of senior-living facilities in the nation, said on a call Thursday that the current flu season has been the worst for seniors in two decades.