Are you sure it is Spring Sickness? I get it every year on a small number of my daylilies but it doesn't spread and doesn't kill them. They just won't bloom that year. The next year they are typically fine. I had a few plants have it this year but we've had so much rain and no hard freezes that some fans have snapped out of it so to speak & may actually bloom this year.
I'm not sure anyone knows exactly what causes the problem or how to fix it. But I wouldn't toss any plants because of it. It may only happen once in any particular cultivar for their entire time in my garden. If I remember correctly there may be other diseases that can cause plants to look the same way and those can spread. If you post a picture of the plants someone might be able to give you a definitive answer.
