Isn't the amount of UV radiation a factor? So while temperature may not slow the spread, the increasing amount of incoming solar radiation as we move into the summer months should be a factor. I know I heard on the radio the other day (and read here at some point) that UV destroys this thing in short order (a matter of minutes, apparently). It's the main reason why I grab the shopping cart that's been sitting way out in the parking lot when I go to the store. Of course, I still wipe the handle with a clorox wipe.