[Arkcon]

Yeah, but more viruses, with more damage ability, all clumped together and ignored by you, can kill the white blood cells sooner, before they become a problem. If they also survive the antibiotic cloud, and you get the biohazard powerup, you can get more of those invisible rbc's. Those guys with the high score (and all the high scores are by the same few guys) have probably latched onto some pretty good formula. And of course, luck figures into it as well.