Okay go to this post: [Release] Unlimited Respawns Trainer! (Now with turn off). Download it.
do all that.
Once you turn this on on Quarantine, Just get your nade and keep nading youself, if you do it fast enough the zombies wont be able to kill you and you will just keep doing this until its all over, one round i had the most points (109) but the most deats (47)