Sabrina, once you're familiar with spring sickness, you can often tell which fans are going to do it even before they do because of the different colour. Sue, the frosty nights appear to be coincidence because if you dig up a daylily that was planning on getting spring sickness before it emerges above the ground and bring it indoors, it will still get spring sickness in the warmth of the house. Also in some years there is no frost after growth starts outside and they still get spring sickness. So it starts even before the fans emerge in spring, it just takes a while for the affected plant parts to grow into view. In many gardens spring sickness can be predicted to make an appearance around the time forsythia blooms.
One member of the unofficial "spring sickness task force" had some reduction in spring sickness with the use of insecticide and fungicide (separately). It may be caused by a combination of factors, the prime suspects currently being bulb mites in cahoots with the leaf streak fungus (Aureobasidium microstictum), but there may be other factors as well, such as soil conditions. I've sometimes wondered if soil pH was another contributing factor but so few people actually know their soil pH it hasn't been possible to do a meaningful survey on that.
